summaryrefslogtreecommitdiff
path: root/lib/fileutils.rb
blob: 74bb904e28143ab91ebdfb4b13abb0aedb288f2b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
# frozen_string_literal: true

begin
  require 'rbconfig'
rescue LoadError
  # for make mjit-headers
end

# Namespace for file utility methods for copying, moving, removing, etc.
#
# == What's Here
#
# First, what’s elsewhere. \Module \FileUtils:
#
# - Inherits from {class Object}[https://docs.ruby-lang.org/en/master/Object.html].
# - Supplements {class File}[https://docs.ruby-lang.org/en/master/File.html]
#   (but is not included or extended there).
#
# Here, module \FileUtils provides methods that are useful for:
#
# - {Creating}[rdoc-ref:FileUtils@Creating].
# - {Deleting}[rdoc-ref:FileUtils@Deleting].
# - {Querying}[rdoc-ref:FileUtils@Querying].
# - {Setting}[rdoc-ref:FileUtils@Setting].
# - {Comparing}[rdoc-ref:FileUtils@Comparing].
# - {Copying}[rdoc-ref:FileUtils@Copying].
# - {Moving}[rdoc-ref:FileUtils@Moving].
# - {Options}[rdoc-ref:FileUtils@Options].
#
# === Creating
#
# - ::mkdir: Creates directories.
# - ::mkdir_p, ::makedirs, ::mkpath: Creates directories,
#   also creating ancestor directories as needed.
# - ::link_entry: Creates a hard link.
# - ::ln, ::link: Creates hard links.
# - ::ln_s, ::symlink: Creates symbolic links.
# - ::ln_sf: Creates symbolic links, overwriting if necessary.
#
# === Deleting
#
# - ::remove_dir: Removes a directory and its descendants.
# - ::remove_entry: Removes an entry, including its descendants if it is a directory.
# - ::remove_entry_secure: Like ::remove_entry, but removes securely.
# - ::remove_file: Removes a file entry.
# - ::rm, ::remove: Removes entries.
# - ::rm_f, ::safe_unlink: Like ::rm, but removes forcibly.
# - ::rm_r: Removes entries and their descendants.
# - ::rm_rf, ::rmtree: Like ::rm_r, but removes forcibly.
# - ::rmdir: Removes directories.
#
# === Querying
#
# - ::pwd, ::getwd: Returns the path to the working directory.
# - ::uptodate?: Returns whether a given entry is newer than given other entries.
#
# === Setting
#
# - ::cd, ::chdir: Sets the working directory.
# - ::chmod: Sets permissions for an entry.
# - ::chmod_R: Sets permissions for an entry and its descendants.
# - ::chown: Sets the owner and group for entries.
# - ::chown_R: Sets the owner and group for entries and their descendants.
# - ::touch: Sets modification and access times for entries,
#   creating if necessary.
#
# === Comparing
#
# - ::compare_file, ::cmp, ::identical?: Returns whether two entries are identical.
# - ::compare_stream: Returns whether two streams are identical.
#
# === Copying
#
# - ::copy_entry: Recursively copies an entry.
# - ::copy_file: Copies an entry.
# - ::copy_stream: Copies a stream.
# - ::cp, ::copy: Copies files.
# - ::cp_lr: Recursively creates hard links.
# - ::cp_r: Recursively copies files, retaining mode, owner, and group.
# - ::install: Recursively copies files, optionally setting mode,
#   owner, and group.
#
# === Moving
#
# - ::mv, ::move: Moves entries.
#
# === Options
#
# - ::collect_method: Returns the names of methods that accept a given option.
# - ::commands: Returns the names of methods that accept options.
# - ::have_option?: Returns whether a given method accepts a given option.
# - ::options: Returns all option names.
# - ::options_of: Returns the names of the options for a given method.
#
# == Path Arguments
#
# Some methods in \FileUtils accept _path_ arguments,
# which are interpreted as paths to filesystem entries:
#
# - If the argument is a string, that value is the path.
# - If the argument has method +:to_path+, it is converted via that method.
# - If the argument has method +:to_str+, it is converted via that method.
#
# == About the Examples
#
# Some examples here involve trees of file entries.
# For these, we sometimes display trees using the
# {tree command-line utility}[https://en.wikipedia.org/wiki/Tree_(command)],
# which is a recursive directory-listing utility that produces
# a depth-indented listing of files and directories.
#
# We use a helper method to launch the command and control the format:
#
#   def tree(dirpath = '.')
#     command = "tree --noreport --charset=ascii #{dirpath}"
#     system(command)
#   end
#
# To illustrate:
#
#   tree('src0')
#   # => src0
#   #    |-- sub0
#   #    |   |-- src0.txt
#   #    |   `-- src1.txt
#   #    `-- sub1
#   #        |-- src2.txt
#   #        `-- src3.txt
#
# == Avoiding the TOCTTOU Vulnerability
#
# For certain methods that recursively remove entries,
# there is a potential vulnerability called the
# {Time-of-check to time-of-use}[https://en.wikipedia.org/wiki/Time-of-check_to_time-of-use],
# or TOCTTOU, vulnerability that can exist when:
#
# - An ancestor directory of the entry at the target path is world writable;
#   such directories include <tt>/tmp</tt>.
# - The directory tree at the target path includes:
#
#   - A world-writable descendant directory.
#   - A symbolic link.
#
# To avoid that vulnerability, you can use this method to remove entries:
#
# - FileUtils.remove_entry_secure: removes recursively
#   if the target path points to a directory.
#
# Also available are these methods,
# each of which calls \FileUtils.remove_entry_secure:
#
# - FileUtils.rm_r with keyword argument <tt>secure: true</tt>.
# - FileUtils.rm_rf with keyword argument <tt>secure: true</tt>.
#
# Finally, this method for moving entries calls \FileUtils.remove_entry_secure
# if the source and destination are on different file systems
# (which means that the "move" is really a copy and remove):
#
# - FileUtils.mv with keyword argument <tt>secure: true</tt>.
#
# \Method \FileUtils.remove_entry_secure removes securely
# by applying a special pre-process:
#
# - If the target path points to a directory, this method uses methods
#   {File#chown}[https://docs.ruby-lang.org/en/master/File.html#method-i-chown]
#   and {File#chmod}[https://docs.ruby-lang.org/en/master/File.html#method-i-chmod]
#   in removing directories.
# - The owner of the target directory should be either the current process
#   or the super user (root).
#
# WARNING: You must ensure that *ALL* parent directories cannot be
# moved by other untrusted users.  For example, parent directories
# should not be owned by untrusted users, and should not be world
# writable except when the sticky bit is set.
#
# For details of this security vulnerability, see Perl cases:
#
# - {CVE-2005-0448}[https://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-0448].
# - {CVE-2004-0452}[https://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0452].
#
module FileUtils
  VERSION = "1.6.0"

  def self.private_module_function(name)   #:nodoc:
    module_function name
    private_class_method name
  end

  #
  # Returns a string containing the path to the current directory:
  #
  #   FileUtils.pwd # => "/rdoc/fileutils"
  #
  # FileUtils.getwd is an alias for FileUtils.pwd.
  #
  # Related: FileUtils.cd.
  #
  def pwd
    Dir.pwd
  end
  module_function :pwd

  alias getwd pwd
  module_function :getwd

  # Changes the working directory to the given +dir+, which
  # should be {interpretable as a path}[rdoc-ref:FileUtils@Path+Arguments]:
  #
  # With no block given,
  # changes the current directory to the directory at +dir+; returns zero:
  #
  #   FileUtils.pwd # => "/rdoc/fileutils"
  #   FileUtils.cd('..')
  #   FileUtils.pwd # => "/rdoc"
  #   FileUtils.cd('fileutils')
  #
  # With a block given, changes the current directory to the directory
  # at +dir+, calls the block with argument +dir+,
  # and restores the original current directory; returns the block's value:
  #
  #   FileUtils.pwd                                     # => "/rdoc/fileutils"
  #   FileUtils.cd('..') { |arg| [arg, FileUtils.pwd] } # => ["..", "/rdoc"]
  #   FileUtils.pwd                                     # => "/rdoc/fileutils"
  #
  # Keyword arguments:
  #
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.cd('..')
  #     FileUtils.cd('fileutils')
  #
  #   Output:
  #
  #     cd ..
  #     cd fileutils
  #
  # FileUtils.chdir is an alias for FileUtils.cd.
  #
  # Related: FileUtils.pwd.
  #
  def cd(dir, verbose: nil, &block) # :yield: dir
    fu_output_message "cd #{dir}" if verbose
    result = Dir.chdir(dir, &block)
    fu_output_message 'cd -' if verbose and block
    result
  end
  module_function :cd

  alias chdir cd
  module_function :chdir

  #
  # Returns +true+ if the file at path +new+
  # is newer than all the files at paths in array +old_list+;
  # +false+ otherwise.
  #
  # Argument +new+ and the elements of +old_list+
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments]:
  #
  #   FileUtils.uptodate?('Rakefile', ['Gemfile', 'README.md']) # => true
  #   FileUtils.uptodate?('Gemfile', ['Rakefile', 'README.md']) # => false
  #
  # A non-existent file is considered to be infinitely old.
  #
  # Related: FileUtils.touch.
  #
  def uptodate?(new, old_list)
    return false unless File.exist?(new)
    new_time = File.mtime(new)
    old_list.each do |old|
      if File.exist?(old)
        return false unless new_time > File.mtime(old)
      end
    end
    true
  end
  module_function :uptodate?

  def remove_trailing_slash(dir)   #:nodoc:
    dir == '/' ? dir : dir.chomp(?/)
  end
  private_module_function :remove_trailing_slash

  #
  # Creates directories at the paths in the given +list+
  # (a single path or an array of paths);
  # returns +list+ if it is an array, <tt>[list]</tt> otherwise.
  #
  # Argument +list+ or its elements
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # With no keyword arguments, creates a directory at each +path+ in +list+
  # by calling: <tt>Dir.mkdir(path, mode)</tt>;
  # see {Dir.mkdir}[https://docs.ruby-lang.org/en/master/Dir.html#method-c-mkdir]:
  #
  #   FileUtils.mkdir(%w[tmp0 tmp1]) # => ["tmp0", "tmp1"]
  #   FileUtils.mkdir('tmp4')        # => ["tmp4"]
  #
  # Keyword arguments:
  #
  # - <tt>mode: <i>mode</i></tt> - also calls <tt>File.chmod(mode, path)</tt>;
  #   see {File.chmod}[https://docs.ruby-lang.org/en/master/File.html#method-c-chmod].
  # - <tt>noop: true</tt> - does not create directories.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.mkdir(%w[tmp0 tmp1], verbose: true)
  #     FileUtils.mkdir(%w[tmp2 tmp3], mode: 0700, verbose: true)
  #
  #   Output:
  #
  #     mkdir tmp0 tmp1
  #     mkdir -m 700 tmp2 tmp3
  #
  # Raises an exception if any path points to an existing
  # file or directory, or if for any reason a directory cannot be created.
  #
  # Related: FileUtils.mkdir_p.
  #
  def mkdir(list, mode: nil, noop: nil, verbose: nil)
    list = fu_list(list)
    fu_output_message "mkdir #{mode ? ('-m %03o ' % mode) : ''}#{list.join ' '}" if verbose
    return if noop

    list.each do |dir|
      fu_mkdir dir, mode
    end
  end
  module_function :mkdir

  #
  # Creates directories at the paths in the given +list+
  # (a single path or an array of paths),
  # also creating ancestor directories as needed;
  # returns +list+ if it is an array, <tt>[list]</tt> otherwise.
  #
  # Argument +list+ or its elements
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # With no keyword arguments, creates a directory at each +path+ in +list+,
  # along with any needed ancestor directories,
  # by calling: <tt>Dir.mkdir(path, mode)</tt>;
  # see {Dir.mkdir}[https://docs.ruby-lang.org/en/master/Dir.html#method-c-mkdir]:
  #
  #   FileUtils.mkdir_p(%w[tmp0/tmp1 tmp2/tmp3]) # => ["tmp0/tmp1", "tmp2/tmp3"]
  #   FileUtils.mkdir_p('tmp4/tmp5')             # => ["tmp4/tmp5"]
  #
  # Keyword arguments:
  #
  # - <tt>mode: <i>mode</i></tt> - also calls <tt>File.chmod(mode, path)</tt>;
  #   see {File.chmod}[https://docs.ruby-lang.org/en/master/File.html#method-c-chmod].
  # - <tt>noop: true</tt> - does not create directories.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.mkdir_p(%w[tmp0 tmp1], verbose: true)
  #     FileUtils.mkdir_p(%w[tmp2 tmp3], mode: 0700, verbose: true)
  #
  #   Output:
  #
  #     mkdir -p tmp0 tmp1
  #     mkdir -p -m 700 tmp2 tmp3
  #
  # Raises an exception if for any reason a directory cannot be created.
  #
  # FileUtils.mkpath and FileUtils.makedirs are aliases for FileUtils.mkdir_p.
  #
  # Related: FileUtils.mkdir.
  #
  def mkdir_p(list, mode: nil, noop: nil, verbose: nil)
    list = fu_list(list)
    fu_output_message "mkdir -p #{mode ? ('-m %03o ' % mode) : ''}#{list.join ' '}" if verbose
    return *list if noop

    list.each do |item|
      path = remove_trailing_slash(item)

      stack = []
      until File.directory?(path) || File.dirname(path) == path
        stack.push path
        path = File.dirname(path)
      end
      stack.reverse_each do |dir|
        begin
          fu_mkdir dir, mode
        rescue SystemCallError
          raise unless File.directory?(dir)
        end
      end
    end

    return *list
  end
  module_function :mkdir_p

  alias mkpath    mkdir_p
  alias makedirs  mkdir_p
  module_function :mkpath
  module_function :makedirs

  def fu_mkdir(path, mode)   #:nodoc:
    path = remove_trailing_slash(path)
    if mode
      Dir.mkdir path, mode
      File.chmod mode, path
    else
      Dir.mkdir path
    end
  end
  private_module_function :fu_mkdir

  #
  # Removes directories at the paths in the given +list+
  # (a single path or an array of paths);
  # returns +list+, if it is an array, <tt>[list]</tt> otherwise.
  #
  # Argument +list+ or its elements
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # With no keyword arguments, removes the directory at each +path+ in +list+,
  # by calling: <tt>Dir.rmdir(path)</tt>;
  # see {Dir.rmdir}[https://docs.ruby-lang.org/en/master/Dir.html#method-c-rmdir]:
  #
  #   FileUtils.rmdir(%w[tmp0/tmp1 tmp2/tmp3]) # => ["tmp0/tmp1", "tmp2/tmp3"]
  #   FileUtils.rmdir('tmp4/tmp5')             # => ["tmp4/tmp5"]
  #
  # Keyword arguments:
  #
  # - <tt>parents: true</tt> - removes successive ancestor directories
  #   if empty.
  # - <tt>noop: true</tt> - does not remove directories.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.rmdir(%w[tmp0/tmp1 tmp2/tmp3], parents: true, verbose: true)
  #     FileUtils.rmdir('tmp4/tmp5', parents: true, verbose: true)
  #
  #   Output:
  #
  #     rmdir -p tmp0/tmp1 tmp2/tmp3
  #     rmdir -p tmp4/tmp5
  #
  # Raises an exception if a directory does not exist
  # or if for any reason a directory cannot be removed.
  #
  # Related: {methods for deleting}[rdoc-ref:FileUtils@Deleting].
  #
  def rmdir(list, parents: nil, noop: nil, verbose: nil)
    list = fu_list(list)
    fu_output_message "rmdir #{parents ? '-p ' : ''}#{list.join ' '}" if verbose
    return if noop
    list.each do |dir|
      Dir.rmdir(dir = remove_trailing_slash(dir))
      if parents
        begin
          until (parent = File.dirname(dir)) == '.' or parent == dir
            dir = parent
            Dir.rmdir(dir)
          end
        rescue Errno::ENOTEMPTY, Errno::EEXIST, Errno::ENOENT
        end
      end
    end
  end
  module_function :rmdir

  # Creates {hard links}[https://en.wikipedia.org/wiki/Hard_link].
  #
  # Arguments +src+ (a single path or an array of paths)
  # and +dest+ (a single path)
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # When +src+ is the path to an existing file
  # and +dest+ is the path to a non-existent file,
  # creates a hard link at +dest+ pointing to +src+; returns zero:
  #
  #   Dir.children('tmp0/')                    # => ["t.txt"]
  #   Dir.children('tmp1/')                    # => []
  #   FileUtils.ln('tmp0/t.txt', 'tmp1/t.lnk') # => 0
  #   Dir.children('tmp1/')                    # => ["t.lnk"]
  #
  # When +src+ is the path to an existing file
  # and +dest+ is the path to an existing directory,
  # creates a hard link at <tt>dest/src</tt> pointing to +src+; returns zero:
  #
  #   Dir.children('tmp2')               # => ["t.dat"]
  #   Dir.children('tmp3')               # => []
  #   FileUtils.ln('tmp2/t.dat', 'tmp3') # => 0
  #   Dir.children('tmp3')               # => ["t.dat"]
  #
  # When +src+ is an array of paths to existing files
  # and +dest+ is the path to an existing directory,
  # then for each path +target+ in +src+,
  # creates a hard link at <tt>dest/target</tt> pointing to +target+;
  # returns +src+:
  #
  #   Dir.children('tmp4/')                               # => []
  #   FileUtils.ln(['tmp0/t.txt', 'tmp2/t.dat'], 'tmp4/') # => ["tmp0/t.txt", "tmp2/t.dat"]
  #   Dir.children('tmp4/')                               # => ["t.dat", "t.txt"]
  #
  # Keyword arguments:
  #
  # - <tt>force: true</tt> - overwrites +dest+ if it exists.
  # - <tt>noop: true</tt> - does not create links.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.ln('tmp0/t.txt', 'tmp1/t.lnk', verbose: true)
  #     FileUtils.ln('tmp2/t.dat', 'tmp3', verbose: true)
  #     FileUtils.ln(['tmp0/t.txt', 'tmp2/t.dat'], 'tmp4/', verbose: true)
  #
  #   Output:
  #
  #     ln tmp0/t.txt tmp1/t.lnk
  #     ln tmp2/t.dat tmp3
  #     ln tmp0/t.txt tmp2/t.dat tmp4/
  #
  # Raises an exception if +dest+ is the path to an existing file
  # and keyword argument +force+ is not +true+.
  #
  # FileUtils#link is an alias for FileUtils#ln.
  #
  # Related: FileUtils.link_entry (has different options).
  #
  def ln(src, dest, force: nil, noop: nil, verbose: nil)
    fu_output_message "ln#{force ? ' -f' : ''} #{[src,dest].flatten.join ' '}" if verbose
    return if noop
    fu_each_src_dest0(src, dest) do |s,d|
      remove_file d, true if force
      File.link s, d
    end
  end
  module_function :ln

  alias link ln
  module_function :link

  # Creates {hard links}[https://en.wikipedia.org/wiki/Hard_link].
  #
  # Arguments +src+ (a single path or an array of paths)
  # and +dest+ (a single path)
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # If +src+ is the path to a directory and +dest+ does not exist,
  # creates links +dest+ and descendents pointing to +src+ and its descendents:
  #
  #   tree('src0')
  #   # => src0
  #   #    |-- sub0
  #   #    |   |-- src0.txt
  #   #    |   `-- src1.txt
  #   #    `-- sub1
  #   #        |-- src2.txt
  #   #        `-- src3.txt
  #   File.exist?('dest0') # => false
  #   FileUtils.cp_lr('src0', 'dest0')
  #   tree('dest0')
  #   # => dest0
  #   #    |-- sub0
  #   #    |   |-- src0.txt
  #   #    |   `-- src1.txt
  #   #    `-- sub1
  #   #        |-- src2.txt
  #   #        `-- src3.txt
  #
  # If +src+ and +dest+ are both paths to directories,
  # creates links <tt>dest/src</tt> and descendents
  # pointing to +src+ and its descendents:
  #
  #   tree('src1')
  #   # => src1
  #   #    |-- sub0
  #   #    |   |-- src0.txt
  #   #    |   `-- src1.txt
  #   #    `-- sub1
  #   #        |-- src2.txt
  #   #        `-- src3.txt
  #   FileUtils.mkdir('dest1')
  #   FileUtils.cp_lr('src1', 'dest1')
  #   tree('dest1')
  #   # => dest1
  #   #    `-- src1
  #   #        |-- sub0
  #   #        |   |-- src0.txt
  #   #        |   `-- src1.txt
  #   #        `-- sub1
  #   #            |-- src2.txt
  #   #            `-- src3.txt
  #
  # If +src+ is an array of paths to entries and +dest+ is the path to a directory,
  # for each path +filepath+ in +src+, creates a link at <tt>dest/filepath</tt>
  # pointing to that path:
  #
  #   tree('src2')
  #   # => src2
  #   #    |-- sub0
  #   #    |   |-- src0.txt
  #   #    |   `-- src1.txt
  #   #    `-- sub1
  #   #        |-- src2.txt
  #   #        `-- src3.txt
  #   FileUtils.mkdir('dest2')
  #   FileUtils.cp_lr(['src2/sub0', 'src2/sub1'], 'dest2')
  #   tree('dest2')
  #   # => dest2
  #   #    |-- sub0
  #   #    |   |-- src0.txt
  #   #    |   `-- src1.txt
  #   #    `-- sub1
  #   #        |-- src2.txt
  #   #        `-- src3.txt
  #
  # Keyword arguments:
  #
  # - <tt>dereference_root: false</tt> - if +src+ is a symbolic link,
  #   does not dereference it.
  # - <tt>noop: true</tt> - does not create links.
  # - <tt>remove_destination: true</tt> - removes +dest+ before creating links.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.cp_lr('src0', 'dest0', noop: true, verbose: true)
  #     FileUtils.cp_lr('src1', 'dest1', noop: true, verbose: true)
  #     FileUtils.cp_lr(['src2/sub0', 'src2/sub1'], 'dest2', noop: true, verbose: true)
  #
  #   Output:
  #
  #     cp -lr src0 dest0
  #     cp -lr src1 dest1
  #     cp -lr src2/sub0 src2/sub1 dest2
  #
  # Raises an exception if +dest+ is the path to an existing file or directory
  # and keyword argument <tt>remove_destination: true</tt> is not given.
  #
  # Related: {methods for copying}[rdoc-ref:FileUtils@Copying].
  #
  def cp_lr(src, dest, noop: nil, verbose: nil,
            dereference_root: true, remove_destination: false)
    fu_output_message "cp -lr#{remove_destination ? ' --remove-destination' : ''} #{[src,dest].flatten.join ' '}" if verbose
    return if noop
    fu_each_src_dest(src, dest) do |s, d|
      link_entry s, d, dereference_root, remove_destination
    end
  end
  module_function :cp_lr

  # Creates {symbolic links}[https://en.wikipedia.org/wiki/Symbolic_link].
  #
  # Arguments +src+ (a single path or an array of paths)
  # and +dest+ (a single path)
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # If +src+ is the path to an existing file:
  #
  # - When +dest+ is the path to a non-existent file,
  #   creates a symbolic link at +dest+ pointing to +src+:
  #
  #     FileUtils.touch('src0.txt')
  #     File.exist?('dest0.txt')   # => false
  #     FileUtils.ln_s('src0.txt', 'dest0.txt')
  #     File.symlink?('dest0.txt') # => true
  #
  # - When +dest+ is the path to an existing file,
  #   creates a symbolic link at +dest+ pointing to +src+
  #   if and only if keyword argument <tt>force: true</tt> is given
  #   (raises an exception otherwise):
  #
  #     FileUtils.touch('src1.txt')
  #     FileUtils.touch('dest1.txt')
  #     FileUtils.ln_s('src1.txt', 'dest1.txt', force: true)
  #     FileTest.symlink?('dest1.txt') # => true
  #
  #     FileUtils.ln_s('src1.txt', 'dest1.txt') # Raises Errno::EEXIST.
  #
  # If +dest+ is the path to a directory,
  # creates a symbolic link at <tt>dest/src</tt> pointing to +src+:
  #
  #   FileUtils.touch('src2.txt')
  #   FileUtils.mkdir('destdir2')
  #   FileUtils.ln_s('src2.txt', 'destdir2')
  #   File.symlink?('destdir2/src2.txt') # => true
  #
  # If +src+ is an array of paths to existing files and +dest+ is a directory,
  # for each child +child+ in +src+ creates a symbolic link <tt>dest/child</tt>
  # pointing to +child+:
  #
  #   FileUtils.mkdir('srcdir3')
  #   FileUtils.touch('srcdir3/src0.txt')
  #   FileUtils.touch('srcdir3/src1.txt')
  #   FileUtils.mkdir('destdir3')
  #   FileUtils.ln_s(['srcdir3/src0.txt', 'srcdir3/src1.txt'], 'destdir3')
  #   File.symlink?('destdir3/src0.txt') # => true
  #   File.symlink?('destdir3/src1.txt') # => true
  #
  # Keyword arguments:
  #
  # - <tt>force: true</tt> - overwrites +dest+ if it exists.
  # - <tt>noop: true</tt> - does not create links.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.ln_s('src0.txt', 'dest0.txt', noop: true, verbose: true)
  #     FileUtils.ln_s('src1.txt', 'destdir1', noop: true, verbose: true)
  #     FileUtils.ln_s('src2.txt', 'dest2.txt', force: true, noop: true, verbose: true)
  #     FileUtils.ln_s(['srcdir3/src0.txt', 'srcdir3/src1.txt'], 'destdir3', noop: true, verbose: true)
  #
  #   Output:
  #
  #     ln -s src0.txt dest0.txt
  #     ln -s src1.txt destdir1
  #     ln -sf src2.txt dest2.txt
  #     ln -s srcdir3/src0.txt srcdir3/src1.txt destdir3
  #
  # FileUtils.symlink is an alias for FileUtils.ln_s.
  #
  # Related: FileUtils.ln_sf.
  #
  def ln_s(src, dest, force: nil, noop: nil, verbose: nil)
    fu_output_message "ln -s#{force ? 'f' : ''} #{[src,dest].flatten.join ' '}" if verbose
    return if noop
    fu_each_src_dest0(src, dest) do |s,d|
      remove_file d, true if force
      File.symlink s, d
    end
  end
  module_function :ln_s

  alias symlink ln_s
  module_function :symlink

  # Like FileUtils.ln_s, but always with keyword argument <tt>force: true</tt> given.
  #
  def ln_sf(src, dest, noop: nil, verbose: nil)
    ln_s src, dest, force: true, noop: noop, verbose: verbose
  end
  module_function :ln_sf

  # Creates {hard links}[https://en.wikipedia.org/wiki/Hard_link]; returns +nil+.
  #
  # Arguments +src+ and +dest+
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # If +src+ is the path to a file and +dest+ does not exist,
  # creates a hard link at +dest+ pointing to +src+:
  #
  #   FileUtils.touch('src0.txt')
  #   File.exist?('dest0.txt') # => false
  #   FileUtils.link_entry('src0.txt', 'dest0.txt')
  #   File.file?('dest0.txt')  # => true
  #
  # If +src+ is the path to a directory and +dest+ does not exist,
  # recursively creates hard links at +dest+ pointing to paths in +src+:
  #
  #   FileUtils.mkdir_p(['src1/dir0', 'src1/dir1'])
  #   src_file_paths = [
  #     'src1/dir0/t0.txt',
  #     'src1/dir0/t1.txt',
  #     'src1/dir1/t2.txt',
  #     'src1/dir1/t3.txt',
  #     ]
  #   FileUtils.touch(src_file_paths)
  #   File.directory?('dest1')        # => true
  #   FileUtils.link_entry('src1', 'dest1')
  #   File.file?('dest1/dir0/t0.txt') # => true
  #   File.file?('dest1/dir0/t1.txt') # => true
  #   File.file?('dest1/dir1/t2.txt') # => true
  #   File.file?('dest1/dir1/t3.txt') # => true
  #
  # Keyword arguments:
  #
  # - <tt>dereference_root: true</tt> - dereferences +src+ if it is a symbolic link.
  # - <tt>remove_destination: true</tt> - removes +dest+ before creating links.
  #
  # Raises an exception if +dest+ is the path to an existing file or directory
  # and keyword argument <tt>remove_destination: true</tt> is not given.
  #
  # Related: FileUtils.ln (has different options).
  #
  def link_entry(src, dest, dereference_root = false, remove_destination = false)
    Entry_.new(src, nil, dereference_root).traverse do |ent|
      destent = Entry_.new(dest, ent.rel, false)
      File.unlink destent.path if remove_destination && File.file?(destent.path)
      ent.link destent.path
    end
  end
  module_function :link_entry

  # Copies files.
  #
  # Arguments +src+ (a single path or an array of paths)
  # and +dest+ (a single path)
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # If +src+ is the path to a file and +dest+ is not the path to a directory,
  # copies +src+ to +dest+:
  #
  #   FileUtils.touch('src0.txt')
  #   File.exist?('dest0.txt') # => false
  #   FileUtils.cp('src0.txt', 'dest0.txt')
  #   File.file?('dest0.txt')  # => true
  #
  # If +src+ is the path to a file and +dest+ is the path to a directory,
  # copies +src+ to <tt>dest/src</tt>:
  #
  #   FileUtils.touch('src1.txt')
  #   FileUtils.mkdir('dest1')
  #   FileUtils.cp('src1.txt', 'dest1')
  #   File.file?('dest1/src1.txt') # => true
  #
  # If +src+ is an array of paths to files and +dest+ is the path to a directory,
  # copies from each +src+ to +dest+:
  #
  #   src_file_paths = ['src2.txt', 'src2.dat']
  #   FileUtils.touch(src_file_paths)
  #   FileUtils.mkdir('dest2')
  #   FileUtils.cp(src_file_paths, 'dest2')
  #   File.file?('dest2/src2.txt') # => true
  #   File.file?('dest2/src2.dat') # => true
  #
  # Keyword arguments:
  #
  # - <tt>preserve: true</tt> - preserves file times.
  # - <tt>noop: true</tt> - does not copy files.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.cp('src0.txt', 'dest0.txt', noop: true, verbose: true)
  #     FileUtils.cp('src1.txt', 'dest1', noop: true, verbose: true)
  #     FileUtils.cp(src_file_paths, 'dest2', noop: true, verbose: true)
  #
  #   Output:
  #
  #     cp src0.txt dest0.txt
  #     cp src1.txt dest1
  #     cp src2.txt src2.dat dest2
  #
  # Raises an exception if +src+ is a directory.
  #
  # FileUtils.copy is an alias for FileUtils.cp.
  #
  # Related: {methods for copying}[rdoc-ref:FileUtils@Copying].
  #
  def cp(src, dest, preserve: nil, noop: nil, verbose: nil)
    fu_output_message "cp#{preserve ? ' -p' : ''} #{[src,dest].flatten.join ' '}" if verbose
    return if noop
    fu_each_src_dest(src, dest) do |s, d|
      copy_file s, d, preserve
    end
  end
  module_function :cp

  alias copy cp
  module_function :copy

  # Recursively copies files.
  #
  # Arguments +src+ (a single path or an array of paths)
  # and +dest+ (a single path)
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # The mode, owner, and group are retained in the copy;
  # to change those, use FileUtils.install instead.
  #
  # If +src+ is the path to a file and +dest+ is not the path to a directory,
  # copies +src+ to +dest+:
  #
  #   FileUtils.touch('src0.txt')
  #   File.exist?('dest0.txt') # => false
  #   FileUtils.cp_r('src0.txt', 'dest0.txt')
  #   File.file?('dest0.txt')  # => true
  #
  # If +src+ is the path to a file and +dest+ is the path to a directory,
  # copies +src+ to <tt>dest/src</tt>:
  #
  #   FileUtils.touch('src1.txt')
  #   FileUtils.mkdir('dest1')
  #   FileUtils.cp_r('src1.txt', 'dest1')
  #   File.file?('dest1/src1.txt') # => true
  #
  # If +src+ is the path to a directory and +dest+ does not exist,
  # recursively copies +src+ to +dest+:
  #
  #   tree('src2')
  #   # => src2
  #   #    |-- dir0
  #   #    |   |-- src0.txt
  #   #    |   `-- src1.txt
  #   #    `-- dir1
  #   #    |-- src2.txt
  #   #    `-- src3.txt
  #   FileUtils.exist?('dest2') # => false
  #   FileUtils.cp_r('src2', 'dest2')
  #   tree('dest2')
  #   # => dest2
  #   #    |-- dir0
  #   #    |   |-- src0.txt
  #   #    |   `-- src1.txt
  #   #    `-- dir1
  #   #    |-- src2.txt
  #   #    `-- src3.txt
  #
  # If +src+ and +dest+ are paths to directories,
  # recursively copies +src+ to <tt>dest/src</tt>:
  #
  #   tree('src3')
  #   # => src3
  #   #    |-- dir0
  #   #    |   |-- src0.txt
  #   #    |   `-- src1.txt
  #   #    `-- dir1
  #   #    |-- src2.txt
  #   #    `-- src3.txt
  #   FileUtils.mkdir('dest3')
  #   FileUtils.cp_r('src3', 'dest3')
  #   tree('dest3')
  #   # => dest3
  #   #    `-- src3
  #   #      |-- dir0
  #   #      |   |-- src0.txt
  #   #      |   `-- src1.txt
  #   #      `-- dir1
  #   #          |-- src2.txt
  #   #          `-- src3.txt
  #
  # If +src+ is an array of paths and +dest+ is a directory,
  # recursively copies from each path in +src+ to +dest+;
  # the paths in +src+ may point to files and/or directories.
  #
  # Keyword arguments:
  #
  # - <tt>dereference_root: false</tt> - if +src+ is a symbolic link,
  #   does not dereference it.
  # - <tt>noop: true</tt> - does not copy files.
  # - <tt>preserve: true</tt> - preserves file times.
  # - <tt>remove_destination: true</tt> - removes +dest+ before copying files.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.cp_r('src0.txt', 'dest0.txt', noop: true, verbose: true)
  #     FileUtils.cp_r('src1.txt', 'dest1', noop: true, verbose: true)
  #     FileUtils.cp_r('src2', 'dest2', noop: true, verbose: true)
  #     FileUtils.cp_r('src3', 'dest3', noop: true, verbose: true)
  #
  #   Output:
  #
  #     cp -r src0.txt dest0.txt
  #     cp -r src1.txt dest1
  #     cp -r src2 dest2
  #     cp -r src3 dest3
  #
  # Raises an exception of +src+ is the path to a directory
  # and +dest+ is the path to a file.
  #
  # Related: {methods for copying}[rdoc-ref:FileUtils@Copying].
  #
  def cp_r(src, dest, preserve: nil, noop: nil, verbose: nil,
           dereference_root: true, remove_destination: nil)
    fu_output_message "cp -r#{preserve ? 'p' : ''}#{remove_destination ? ' --remove-destination' : ''} #{[src,dest].flatten.join ' '}" if verbose
    return if noop
    fu_each_src_dest(src, dest) do |s, d|
      copy_entry s, d, preserve, dereference_root, remove_destination
    end
  end
  module_function :cp_r

  # Recursively copies files from +src+ to +dest+.
  #
  # Arguments +src+ and +dest+
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # If +src+ is the path to a file, copies +src+ to +dest+:
  #
  #   FileUtils.touch('src0.txt')
  #   File.exist?('dest0.txt') # => false
  #   FileUtils.copy_entry('src0.txt', 'dest0.txt')
  #   File.file?('dest0.txt')  # => true
  #
  # If +src+ is a directory, recursively copies +src+ to +dest+:
  #
  #   tree('src1')
  #   # => src1
  #   #    |-- dir0
  #   #    |   |-- src0.txt
  #   #    |   `-- src1.txt
  #   #    `-- dir1
  #   #        |-- src2.txt
  #   #        `-- src3.txt
  #   FileUtils.copy_entry('src1', 'dest1')
  #   tree('dest1')
  #   # => dest1
  #   #    |-- dir0
  #   #    |   |-- src0.txt
  #   #    |   `-- src1.txt
  #   #    `-- dir1
  #   #        |-- src2.txt
  #   #        `-- src3.txt
  #
  # The recursive copying preserves file types for regular files,
  # directories, and symbolic links;
  # other file types (FIFO streams, device files, etc.) are not supported.
  #
  # Keyword arguments:
  #
  # - <tt>dereference_root: true</tt> - if +src+ is a symbolic link,
  #   follows the link.
  # - <tt>preserve: true</tt> - preserves file times.
  # - <tt>remove_destination: true</tt> - removes +dest+ before copying files.
  #
  # Related: {methods for copying}[rdoc-ref:FileUtils@Copying].
  #
  def copy_entry(src, dest, preserve = false, dereference_root = false, remove_destination = false)
    if dereference_root
      src = File.realpath(src)
    end

    Entry_.new(src, nil, false).wrap_traverse(proc do |ent|
      destent = Entry_.new(dest, ent.rel, false)
      File.unlink destent.path if remove_destination && (File.file?(destent.path) || File.symlink?(destent.path))
      ent.copy destent.path
    end, proc do |ent|
      destent = Entry_.new(dest, ent.rel, false)
      ent.copy_metadata destent.path if preserve
    end)
  end
  module_function :copy_entry

  # Copies file from +src+ to +dest+, which should not be directories.
  #
  # Arguments +src+ and +dest+
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # Examples:
  #
  #   FileUtils.touch('src0.txt')
  #   FileUtils.copy_file('src0.txt', 'dest0.txt')
  #   File.file?('dest0.txt') # => true
  #
  # Keyword arguments:
  #
  # - <tt>dereference: false</tt> - if +src+ is a symbolic link,
  #   does not follow the link.
  # - <tt>preserve: true</tt> - preserves file times.
  # - <tt>remove_destination: true</tt> - removes +dest+ before copying files.
  #
  # Related: {methods for copying}[rdoc-ref:FileUtils@Copying].
  #
  def copy_file(src, dest, preserve = false, dereference = true)
    ent = Entry_.new(src, nil, dereference)
    ent.copy_file dest
    ent.copy_metadata dest if preserve
  end
  module_function :copy_file

  # Copies \IO stream +src+ to \IO stream +dest+ via
  # {IO.copy_stream}[https://docs.ruby-lang.org/en/master/IO.html#method-c-copy_stream].
  #
  # Related: {methods for copying}[rdoc-ref:FileUtils@Copying].
  #
  def copy_stream(src, dest)
    IO.copy_stream(src, dest)
  end
  module_function :copy_stream

  # Moves entries.
  #
  # Arguments +src+ (a single path or an array of paths)
  # and +dest+ (a single path)
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # If +src+ and +dest+ are on different file systems,
  # first copies, then removes +src+.
  #
  # May cause a local vulnerability if not called with keyword argument
  # <tt>secure: true</tt>;
  # see {Avoiding the TOCTTOU Vulnerability}[rdoc-ref:FileUtils@Avoiding+the+TOCTTOU+Vulnerability].
  #
  # If +src+ is the path to a single file or directory and +dest+ does not exist,
  # moves +src+ to +dest+:
  #
  #   tree('src0')
  #   # => src0
  #   #    |-- src0.txt
  #   #    `-- src1.txt
  #   File.exist?('dest0') # => false
  #   FileUtils.mv('src0', 'dest0')
  #   File.exist?('src0')  # => false
  #   tree('dest0')
  #   # => dest0
  #   #    |-- src0.txt
  #   #    `-- src1.txt
  #
  # If +src+ is an array of paths to files and directories
  # and +dest+ is the path to a directory,
  # copies from each path in the array to +dest+:
  #
  #   File.file?('src1.txt') # => true
  #   tree('src1')
  #   # => src1
  #   #    |-- src.dat
  #   #    `-- src.txt
  #   Dir.empty?('dest1')    # => true
  #   FileUtils.mv(['src1.txt', 'src1'], 'dest1')
  #   tree('dest1')
  #   # => dest1
  #   #    |-- src1
  #   #    |   |-- src.dat
  #   #    |   `-- src.txt
  #   #    `-- src1.txt
  #
  # Keyword arguments:
  #
  # - <tt>force: true</tt> - if the move includes removing +src+
  #   (that is, if +src+ and +dest+ are on different file systems),
  #   ignores raised exceptions of StandardError and its descendants.
  # - <tt>noop: true</tt> - does not move files.
  # - <tt>secure: true</tt> - removes +src+ securely;
  #   see details at FileUtils.remove_entry_secure.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.mv('src0', 'dest0', noop: true, verbose: true)
  #     FileUtils.mv(['src1.txt', 'src1'], 'dest1', noop: true, verbose: true)
  #
  #   Output:
  #
  #     mv src0 dest0
  #     mv src1.txt src1 dest1
  #
  # FileUtils.move is an alias for FileUtils.mv.
  #
  def mv(src, dest, force: nil, noop: nil, verbose: nil, secure: nil)
    fu_output_message "mv#{force ? ' -f' : ''} #{[src,dest].flatten.join ' '}" if verbose
    return if noop
    fu_each_src_dest(src, dest) do |s, d|
      destent = Entry_.new(d, nil, true)
      begin
        if destent.exist?
          if destent.directory?
            raise Errno::EEXIST, d
          end
        end
        begin
          File.rename s, d
        rescue Errno::EXDEV,
               Errno::EPERM # move from unencrypted to encrypted dir (ext4)
          copy_entry s, d, true
          if secure
            remove_entry_secure s, force
          else
            remove_entry s, force
          end
        end
      rescue SystemCallError
        raise unless force
      end
    end
  end
  module_function :mv

  alias move mv
  module_function :move

  # Removes entries at the paths in the given +list+
  # (a single path or an array of paths)
  # returns +list+, if it is an array, <tt>[list]</tt> otherwise.
  #
  # Argument +list+ or its elements
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # With no keyword arguments, removes files at the paths given in +list+:
  #
  #   FileUtils.touch(['src0.txt', 'src0.dat'])
  #   FileUtils.rm(['src0.dat', 'src0.txt']) # => ["src0.dat", "src0.txt"]
  #
  # Keyword arguments:
  #
  # - <tt>force: true</tt> - ignores raised exceptions of Errno::ENOENT
  #   and its descendants.
  # - <tt>noop: true</tt> - does not remove files; returns +nil+.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.rm(['src0.dat', 'src0.txt'], noop: true, verbose: true)
  #
  #   Output:
  #
  #     rm src0.dat src0.txt
  #
  # FileUtils.remove is an alias for FileUtils.rm.
  #
  # Related: {methods for deleting}[rdoc-ref:FileUtils@Deleting].
  #
  def rm(list, force: nil, noop: nil, verbose: nil)
    list = fu_list(list)
    fu_output_message "rm#{force ? ' -f' : ''} #{list.join ' '}" if verbose
    return if noop

    list.each do |path|
      remove_file path, force
    end
  end
  module_function :rm

  alias remove rm
  module_function :remove

  # Equivalent to:
  #
  #   FileUtils.rm(list, force: true, **kwargs)
  #
  # Argument +list+ (a single path or an array of paths)
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # See FileUtils.rm for keyword arguments.
  #
  # FileUtils.safe_unlink is an alias for FileUtils.rm_f.
  #
  # Related: {methods for deleting}[rdoc-ref:FileUtils@Deleting].
  #
  def rm_f(list, noop: nil, verbose: nil)
    rm list, force: true, noop: noop, verbose: verbose
  end
  module_function :rm_f

  alias safe_unlink rm_f
  module_function :safe_unlink

  # Removes entries at the paths in the given +list+
  # (a single path or an array of paths);
  # returns +list+, if it is an array, <tt>[list]</tt> otherwise.
  #
  # Argument +list+ or its elements
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # May cause a local vulnerability if not called with keyword argument
  # <tt>secure: true</tt>;
  # see {Avoiding the TOCTTOU Vulnerability}[rdoc-ref:FileUtils@Avoiding+the+TOCTTOU+Vulnerability].
  #
  # For each file path, removes the file at that path:
  #
  #   FileUtils.touch(['src0.txt', 'src0.dat'])
  #   FileUtils.rm_r(['src0.dat', 'src0.txt'])
  #   File.exist?('src0.txt') # => false
  #   File.exist?('src0.dat') # => false
  #
  # For each directory path, recursively removes files and directories:
  #
  #   tree('src1')
  #   # => src1
  #   #    |-- dir0
  #   #    |   |-- src0.txt
  #   #    |   `-- src1.txt
  #   #    `-- dir1
  #   #        |-- src2.txt
  #   #        `-- src3.txt
  #   FileUtils.rm_r('src1')
  #   File.exist?('src1') # => false
  #
  # Keyword arguments:
  #
  # - <tt>force: true</tt> - ignores raised exceptions of Errno::ENOENT
  #   and its descendants.
  # - <tt>noop: true</tt> - does not remove entries; returns +nil+.
  # - <tt>secure: true</tt> - removes +src+ securely;
  #   see details at FileUtils.remove_entry_secure.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.rm_r(['src0.dat', 'src0.txt'], noop: true, verbose: true)
  #     FileUtils.rm_r('src1', noop: true, verbose: true)
  #
  #   Output:
  #
  #     rm -r src0.dat src0.txt
  #     rm -r src1
  #
  # Related: {methods for deleting}[rdoc-ref:FileUtils@Deleting].
  #
  def rm_r(list, force: nil, noop: nil, verbose: nil, secure: nil)
    list = fu_list(list)
    fu_output_message "rm -r#{force ? 'f' : ''} #{list.join ' '}" if verbose
    return if noop
    list.each do |path|
      if secure
        remove_entry_secure path, force
      else
        remove_entry path, force
      end
    end
  end
  module_function :rm_r

  # Equivalent to:
  #
  #   FileUtils.rm_r(list, force: true, **kwargs)
  #
  # Argument +list+ or its elements
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # May cause a local vulnerability if not called with keyword argument
  # <tt>secure: true</tt>;
  # see {Avoiding the TOCTTOU Vulnerability}[rdoc-ref:FileUtils@Avoiding+the+TOCTTOU+Vulnerability].
  #
  # See FileUtils.rm_r for keyword arguments.
  #
  # FileUtils.rmtree is an alias for FileUtils.rm_rf.
  #
  # Related: {methods for deleting}[rdoc-ref:FileUtils@Deleting].
  #
  def rm_rf(list, noop: nil, verbose: nil, secure: nil)
    rm_r list, force: true, noop: noop, verbose: verbose, secure: secure
  end
  module_function :rm_rf

  alias rmtree rm_rf
  module_function :rmtree

  # Securely removes the entry given by +path+,
  # which should be the entry for a regular file, a symbolic link,
  # or a directory.
  #
  # Argument +path+
  # should be {interpretable as a path}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # Avoids a local vulnerability that can exist in certain circumstances;
  # see {Avoiding the TOCTTOU Vulnerability}[rdoc-ref:FileUtils@Avoiding+the+TOCTTOU+Vulnerability].
  #
  # Optional argument +force+ specifies whether to ignore
  # raised exceptions of Errno::ENOENT and its descendants.
  #
  # Related: {methods for deleting}[rdoc-ref:FileUtils@Deleting].
  #
  def remove_entry_secure(path, force = false)
    unless fu_have_symlink?
      remove_entry path, force
      return
    end
    fullpath = File.expand_path(path)
    st = File.lstat(fullpath)
    unless st.directory?
      File.unlink fullpath
      return
    end
    # is a directory.
    parent_st = File.stat(File.dirname(fullpath))
    unless parent_st.world_writable?
      remove_entry path, force
      return
    end
    unless parent_st.sticky?
      raise ArgumentError, "parent directory is world writable, FileUtils#remove_entry_secure does not work; abort: #{path.inspect} (parent directory mode #{'%o' % parent_st.mode})"
    end

    # freeze tree root
    euid = Process.euid
    dot_file = fullpath + "/."
    begin
      File.open(dot_file) {|f|
        unless fu_stat_identical_entry?(st, f.stat)
          # symlink (TOC-to-TOU attack?)
          File.unlink fullpath
          return
        end
        f.chown euid, -1
        f.chmod 0700
      }
    rescue Errno::EISDIR # JRuby in non-native mode can't open files as dirs
      File.lstat(dot_file).tap {|fstat|
        unless fu_stat_identical_entry?(st, fstat)
          # symlink (TOC-to-TOU attack?)
          File.unlink fullpath
          return
        end
        File.chown euid, -1, dot_file
        File.chmod 0700, dot_file
      }
    end

    unless fu_stat_identical_entry?(st, File.lstat(fullpath))
      # TOC-to-TOU attack?
      File.unlink fullpath
      return
    end

    # ---- tree root is frozen ----
    root = Entry_.new(path)
    root.preorder_traverse do |ent|
      if ent.directory?
        ent.chown euid, -1
        ent.chmod 0700
      end
    end
    root.postorder_traverse do |ent|
      begin
        ent.remove
      rescue
        raise unless force
        raise unless Errno::ENOENT === $!
      end
    end
  rescue
    raise unless force
    raise unless Errno::ENOENT === $!
  end
  module_function :remove_entry_secure

  def fu_have_symlink?   #:nodoc:
    File.symlink nil, nil
  rescue NotImplementedError
    return false
  rescue TypeError
    return true
  end
  private_module_function :fu_have_symlink?

  def fu_stat_identical_entry?(a, b)   #:nodoc:
    a.dev == b.dev and a.ino == b.ino
  end
  private_module_function :fu_stat_identical_entry?

  # Removes the entry given by +path+,
  # which should be the entry for a regular file, a symbolic link,
  # or a directory.
  #
  # Argument +path+
  # should be {interpretable as a path}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # Optional argument +force+ specifies whether to ignore
  # raised exceptions of Errno::ENOENT and its descendants.
  #
  # Related: FileUtils.remove_entry_secure.
  #
  def remove_entry(path, force = false)
    Entry_.new(path).postorder_traverse do |ent|
      begin
        ent.remove
      rescue
        raise unless force
        raise unless Errno::ENOENT === $!
      end
    end
  rescue
    raise unless force
    raise unless Errno::ENOENT === $!
  end
  module_function :remove_entry

  # Removes the file entry given by +path+,
  # which should be the entry for a regular file or a symbolic link.
  #
  # Argument +path+
  # should be {interpretable as a path}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # Optional argument +force+ specifies whether to ignore
  # raised exceptions of Errno::ENOENT and its descendants.
  #
  # Related: {methods for deleting}[rdoc-ref:FileUtils@Deleting].
  #
  def remove_file(path, force = false)
    Entry_.new(path).remove_file
  rescue
    raise unless force
    raise unless Errno::ENOENT === $!
  end
  module_function :remove_file

  # Recursively removes the directory entry given by +path+,
  # which should be the entry for a regular file, a symbolic link,
  # or a directory.
  #
  # Argument +path+
  # should be {interpretable as a path}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # Optional argument +force+ specifies whether to ignore
  # raised exceptions of Errno::ENOENT and its descendants.
  #
  # Related: {methods for deleting}[rdoc-ref:FileUtils@Deleting].
  #
  def remove_dir(path, force = false)
    remove_entry path, force   # FIXME?? check if it is a directory
  end
  module_function :remove_dir

  # Returns +true+ if the contents of files +a+ and +b+ are identical,
  # +false+ otherwise.
  #
  # Arguments +a+ and +b+
  # should be {interpretable as a path}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # FileUtils.identical? and FileUtils.cmp are aliases for FileUtils.compare_file.
  #
  # Related: FileUtils.compare_stream.
  #
  def compare_file(a, b)
    return false unless File.size(a) == File.size(b)
    File.open(a, 'rb') {|fa|
      File.open(b, 'rb') {|fb|
        return compare_stream(fa, fb)
      }
    }
  end
  module_function :compare_file

  alias identical? compare_file
  alias cmp compare_file
  module_function :identical?
  module_function :cmp

  # Returns +true+ if the contents of streams +a+ and +b+ are identical,
  # +false+ otherwise.
  #
  # Arguments +a+ and +b+
  # should be {interpretable as a path}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # Related: FileUtils.compare_file.
  #
  def compare_stream(a, b)
    bsize = fu_stream_blksize(a, b)

    sa = String.new(capacity: bsize)
    sb = String.new(capacity: bsize)

    begin
      a.read(bsize, sa)
      b.read(bsize, sb)
      return true if sa.empty? && sb.empty?
    end while sa == sb
    false
  end
  module_function :compare_stream

  # Copies a file entry.
  # See {install(1)}[https://man7.org/linux/man-pages/man1/install.1.html].
  #
  # Arguments +src+ (a single path or an array of paths)
  # and +dest+ (a single path)
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments];
  #
  # If the entry at +dest+ does not exist, copies from +src+ to +dest+:
  #
  #   File.read('src0.txt')    # => "aaa\n"
  #   File.exist?('dest0.txt') # => false
  #   FileUtils.install('src0.txt', 'dest0.txt')
  #   File.read('dest0.txt')   # => "aaa\n"
  #
  # If +dest+ is a file entry, copies from +src+ to +dest+, overwriting:
  #
  #   File.read('src1.txt')  # => "aaa\n"
  #   File.read('dest1.txt') # => "bbb\n"
  #   FileUtils.install('src1.txt', 'dest1.txt')
  #   File.read('dest1.txt') # => "aaa\n"
  #
  # If +dest+ is a directory entry, copies from +src+ to <tt>dest/src</tt>,
  # overwriting if necessary:
  #
  #   File.read('src2.txt')       # => "aaa\n"
  #   File.read('dest2/src2.txt') # => "bbb\n"
  #   FileUtils.install('src2.txt', 'dest2')
  #   File.read('dest2/src2.txt') # => "aaa\n"
  #
  # If +src+ is an array of paths and +dest+ points to a directory,
  # copies each path +path+ in +src+ to <tt>dest/path</tt>:
  #
  #   File.file?('src3.txt') # => true
  #   File.file?('src3.dat') # => true
  #   FileUtils.mkdir('dest3')
  #   FileUtils.install(['src3.txt', 'src3.dat'], 'dest3')
  #   File.file?('dest3/src3.txt') # => true
  #   File.file?('dest3/src3.dat') # => true
  #
  # Keyword arguments:
  #
  # - <tt>group: <i>group</i></tt> - changes the group if not +nil+,
  #   using {File.chown}[https://docs.ruby-lang.org/en/master/File.html#method-c-chown].
  # - <tt>mode: <i>permissions</i></tt> - changes the permissions.
  #   using {File.chmod}[https://docs.ruby-lang.org/en/master/File.html#method-c-chmod].
  # - <tt>noop: true</tt> - does not copy entries; returns +nil+.
  # - <tt>owner: <i>owner</i></tt> - changes the owner if not +nil+,
  #   using {File.chown}[https://docs.ruby-lang.org/en/master/File.html#method-c-chown].
  # - <tt>preserve: true</tt> - preserve timestamps
  #   using {File.utime}[https://docs.ruby-lang.org/en/master/File.html#method-c-utime].
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.install('src0.txt', 'dest0.txt', noop: true, verbose: true)
  #     FileUtils.install('src1.txt', 'dest1.txt', noop: true, verbose: true)
  #     FileUtils.install('src2.txt', 'dest2', noop: true, verbose: true)
  #
  #   Output:
  #
  #     install -c src0.txt dest0.txt
  #     install -c src1.txt dest1.txt
  #     install -c src2.txt dest2
  #
  # Related: {methods for copying}[rdoc-ref:FileUtils@Copying].
  #
  def install(src, dest, mode: nil, owner: nil, group: nil, preserve: nil,
              noop: nil, verbose: nil)
    if verbose
      msg = +"install -c"
      msg << ' -p' if preserve
      msg << ' -m ' << mode_to_s(mode) if mode
      msg << " -o #{owner}" if owner
      msg << " -g #{group}" if group
      msg << ' ' << [src,dest].flatten.join(' ')
      fu_output_message msg
    end
    return if noop
    uid = fu_get_uid(owner)
    gid = fu_get_gid(group)
    fu_each_src_dest(src, dest) do |s, d|
      st = File.stat(s)
      unless File.exist?(d) and compare_file(s, d)
        remove_file d, true
        copy_file s, d
        File.utime st.atime, st.mtime, d if preserve
        File.chmod fu_mode(mode, st), d if mode
        File.chown uid, gid, d if uid or gid
      end
    end
  end
  module_function :install

  def user_mask(target)  #:nodoc:
    target.each_char.inject(0) do |mask, chr|
      case chr
      when "u"
        mask | 04700
      when "g"
        mask | 02070
      when "o"
        mask | 01007
      when "a"
        mask | 07777
      else
        raise ArgumentError, "invalid `who' symbol in file mode: #{chr}"
      end
    end
  end
  private_module_function :user_mask

  def apply_mask(mode, user_mask, op, mode_mask)   #:nodoc:
    case op
    when '='
      (mode & ~user_mask) | (user_mask & mode_mask)
    when '+'
      mode | (user_mask & mode_mask)
    when '-'
      mode & ~(user_mask & mode_mask)
    end
  end
  private_module_function :apply_mask

  def symbolic_modes_to_i(mode_sym, path)  #:nodoc:
    path = File.stat(path) unless File::Stat === path
    mode = path.mode
    mode_sym.split(/,/).inject(mode & 07777) do |current_mode, clause|
      target, *actions = clause.split(/([=+-])/)
      raise ArgumentError, "invalid file mode: #{mode_sym}" if actions.empty?
      target = 'a' if target.empty?
      user_mask = user_mask(target)
      actions.each_slice(2) do |op, perm|
        need_apply = op == '='
        mode_mask = (perm || '').each_char.inject(0) do |mask, chr|
          case chr
          when "r"
            mask | 0444
          when "w"
            mask | 0222
          when "x"
            mask | 0111
          when "X"
            if path.directory?
              mask | 0111
            else
              mask
            end
          when "s"
            mask | 06000
          when "t"
            mask | 01000
          when "u", "g", "o"
            if mask.nonzero?
              current_mode = apply_mask(current_mode, user_mask, op, mask)
            end
            need_apply = false
            copy_mask = user_mask(chr)
            (current_mode & copy_mask) / (copy_mask & 0111) * (user_mask & 0111)
          else
            raise ArgumentError, "invalid `perm' symbol in file mode: #{chr}"
          end
        end

        if mode_mask.nonzero? || need_apply
          current_mode = apply_mask(current_mode, user_mask, op, mode_mask)
        end
      end
      current_mode
    end
  end
  private_module_function :symbolic_modes_to_i

  def fu_mode(mode, path)  #:nodoc:
    mode.is_a?(String) ? symbolic_modes_to_i(mode, path) : mode
  end
  private_module_function :fu_mode

  def mode_to_s(mode)  #:nodoc:
    mode.is_a?(String) ? mode : "%o" % mode
  end
  private_module_function :mode_to_s

  # Changes permissions on the entries at the paths given in +list+
  # (a single path or an array of paths)
  # to the permissions given by +mode+;
  # returns +list+ if it is an array, <tt>[list]</tt> otherwise:
  #
  # - Modifies each entry that is a regular file using
  #   {File.chmod}[https://docs.ruby-lang.org/en/master/File.html#method-c-chmod].
  # - Modifies each entry that is a symbolic link using
  #   {File.lchmod}[https://docs.ruby-lang.org/en/master/File.html#method-c-lchmod].
  #
  # Argument +list+ or its elements
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # Argument +mode+ may be either an integer or a string:
  #
  # - \Integer +mode+: represents the permission bits to be set:
  #
  #     FileUtils.chmod(0755, 'src0.txt')
  #     FileUtils.chmod(0644, ['src0.txt', 'src0.dat'])
  #
  # - \String +mode+: represents the permissions to be set:
  #
  #   The string is of the form <tt>[targets][[operator][perms[,perms]]</tt>, where:
  #
  #   - +targets+ may be any combination of these letters:
  #
  #     - <tt>'u'</tt>: permissions apply to the file's owner.
  #     - <tt>'g'</tt>: permissions apply to users in the file's group.
  #     - <tt>'o'</tt>: permissions apply to other users not in the file's group.
  #     - <tt>'a'</tt> (the default): permissions apply to all users.
  #
  #   - +operator+ may be one of these letters:
  #
  #     - <tt>'+'</tt>: adds permissions.
  #     - <tt>'-'</tt>: removes permissions.
  #     - <tt>'='</tt>: sets (replaces) permissions.
  #
  #   - +perms+ (may be repeated, with separating commas)
  #     may be any combination of these letters:
  #
  #     - <tt>'r'</tt>: Read.
  #     - <tt>'w'</tt>: Write.
  #     - <tt>'x'</tt>: Execute (search, for a directory).
  #     - <tt>'X'</tt>: Search (for a directories only;
  #       must be used with <tt>'+'</tt>)
  #     - <tt>'s'</tt>: Uid or gid.
  #     - <tt>'t'</tt>: Sticky bit.
  #
  #   Examples:
  #
  #     FileUtils.chmod('u=wrx,go=rx', 'src1.txt')
  #     FileUtils.chmod('u=wrx,go=rx', '/usr/bin/ruby')
  #
  # Keyword arguments:
  #
  # - <tt>noop: true</tt> - does not change permissions; returns +nil+.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.chmod(0755, 'src0.txt', noop: true, verbose: true)
  #     FileUtils.chmod(0644, ['src0.txt', 'src0.dat'], noop: true, verbose: true)
  #     FileUtils.chmod('u=wrx,go=rx', 'src1.txt', noop: true, verbose: true)
  #     FileUtils.chmod('u=wrx,go=rx', '/usr/bin/ruby', noop: true, verbose: true)
  #
  #   Output:
  #
  #     chmod 755 src0.txt
  #     chmod 644 src0.txt src0.dat
  #     chmod u=wrx,go=rx src1.txt
  #     chmod u=wrx,go=rx /usr/bin/ruby
  #
  # Related: FileUtils.chmod_R.
  #
  def chmod(mode, list, noop: nil, verbose: nil)
    list = fu_list(list)
    fu_output_message sprintf('chmod %s %s', mode_to_s(mode), list.join(' ')) if verbose
    return if noop
    list.each do |path|
      Entry_.new(path).chmod(fu_mode(mode, path))
    end
  end
  module_function :chmod

  # Like FileUtils.chmod, but changes permissions recursively.
  #
  def chmod_R(mode, list, noop: nil, verbose: nil, force: nil)
    list = fu_list(list)
    fu_output_message sprintf('chmod -R%s %s %s',
                              (force ? 'f' : ''),
                              mode_to_s(mode), list.join(' ')) if verbose
    return if noop
    list.each do |root|
      Entry_.new(root).traverse do |ent|
        begin
          ent.chmod(fu_mode(mode, ent.path))
        rescue
          raise unless force
        end
      end
    end
  end
  module_function :chmod_R

  # Changes the owner and group on the entries at the paths given in +list+
  # (a single path or an array of paths)
  # to the given +user+ and +group+;
  # returns +list+ if it is an array, <tt>[list]</tt> otherwise:
  #
  # - Modifies each entry that is a regular file using
  #   {File.chown}[https://docs.ruby-lang.org/en/master/File.html#method-c-chown].
  # - Modifies each entry that is a symbolic link using
  #   {File.lchown}[https://docs.ruby-lang.org/en/master/File.html#method-c-lchown].
  #
  # Argument +list+ or its elements
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # User and group:
  #
  # - Argument +user+ may be a user name or a user id;
  #   if +nil+ or +-1+, the user is not changed.
  # - Argument +group+ may be a group name or a group id;
  #   if +nil+ or +-1+, the group is not changed.
  # - The user must be a member of the group.
  #
  # Examples:
  #
  #   # One path.
  #   # User and group as string names.
  #   File.stat('src0.txt').uid # => 1004
  #   File.stat('src0.txt').gid # => 1004
  #   FileUtils.chown('user2', 'group1', 'src0.txt')
  #   File.stat('src0.txt').uid # => 1006
  #   File.stat('src0.txt').gid # => 1005
  #
  #   # User and group as uid and gid.
  #   FileUtils.chown(1004, 1004, 'src0.txt')
  #   File.stat('src0.txt').uid # => 1004
  #   File.stat('src0.txt').gid # => 1004
  #
  #   # Array of paths.
  #   FileUtils.chown(1006, 1005, ['src0.txt', 'src0.dat'])
  #
  #   # Directory (not recursive).
  #   FileUtils.chown('user2', 'group1', '.')
  #
  # Keyword arguments:
  #
  # - <tt>noop: true</tt> - does not change permissions; returns +nil+.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.chown('user2', 'group1', 'src0.txt', noop: true, verbose: true)
  #     FileUtils.chown(1004, 1004, 'src0.txt', noop: true, verbose: true)
  #     FileUtils.chown(1006, 1005, ['src0.txt', 'src0.dat'], noop: true, verbose: true)
  #     FileUtils.chown('user2', 'group1', path, noop: true, verbose: true)
  #     FileUtils.chown('user2', 'group1', '.', noop: true, verbose: true)
  #
  #   Output:
  #
  #     chown user2:group1 src0.txt
  #     chown 1004:1004 src0.txt
  #     chown 1006:1005 src0.txt src0.dat
  #     chown user2:group1 src0.txt
  #     chown user2:group1 .
  #
  # Related: FileUtils.chown_R.
  #
  def chown(user, group, list, noop: nil, verbose: nil)
    list = fu_list(list)
    fu_output_message sprintf('chown %s %s',
                              (group ? "#{user}:#{group}" : user || ':'),
                              list.join(' ')) if verbose
    return if noop
    uid = fu_get_uid(user)
    gid = fu_get_gid(group)
    list.each do |path|
      Entry_.new(path).chown uid, gid
    end
  end
  module_function :chown

  # Like FileUtils.chown, but changes owner and group recursively.
  #
  def chown_R(user, group, list, noop: nil, verbose: nil, force: nil)
    list = fu_list(list)
    fu_output_message sprintf('chown -R%s %s %s',
                              (force ? 'f' : ''),
                              (group ? "#{user}:#{group}" : user || ':'),
                              list.join(' ')) if verbose
    return if noop
    uid = fu_get_uid(user)
    gid = fu_get_gid(group)
    list.each do |root|
      Entry_.new(root).traverse do |ent|
        begin
          ent.chown uid, gid
        rescue
          raise unless force
        end
      end
    end
  end
  module_function :chown_R

  def fu_get_uid(user)   #:nodoc:
    return nil unless user
    case user
    when Integer
      user
    when /\A\d+\z/
      user.to_i
    else
      require 'etc'
      Etc.getpwnam(user) ? Etc.getpwnam(user).uid : nil
    end
  end
  private_module_function :fu_get_uid

  def fu_get_gid(group)   #:nodoc:
    return nil unless group
    case group
    when Integer
      group
    when /\A\d+\z/
      group.to_i
    else
      require 'etc'
      Etc.getgrnam(group) ? Etc.getgrnam(group).gid : nil
    end
  end
  private_module_function :fu_get_gid

  # Updates modification times (mtime) and access times (atime)
  # of the entries given by the paths in +list+
  # (a single path or an array of paths);
  # returns +list+ if it is an array, <tt>[list]</tt> otherwise.
  #
  # By default, creates an empty file for any path to a non-existent entry;
  # use keyword argument +nocreate+ to raise an exception instead.
  #
  # Argument +list+ or its elements
  # should be {interpretable as paths}[rdoc-ref:FileUtils@Path+Arguments].
  #
  # Examples:
  #
  #   # Single path.
  #   f = File.new('src0.txt') # Existing file.
  #   f.atime # => 2022-06-10 11:11:21.200277 -0700
  #   f.mtime # => 2022-06-10 11:11:21.200277 -0700
  #   FileUtils.touch('src0.txt')
  #   f = File.new('src0.txt')
  #   f.atime # => 2022-06-11 08:28:09.8185343 -0700
  #   f.mtime # => 2022-06-11 08:28:09.8185343 -0700
  #
  #   # Array of paths.
  #   FileUtils.touch(['src0.txt', 'src0.dat'])
  #
  # Keyword arguments:
  #
  # - <tt>mtime: <i>time</i></tt> - sets the entry's mtime to the given time,
  #   instead of the current time.
  # - <tt>nocreate: true</tt> - raises an exception if the entry does not exist.
  # - <tt>noop: true</tt> - does not touch entries; returns +nil+.
  # - <tt>verbose: true</tt> - prints an equivalent command:
  #
  #     FileUtils.touch('src0.txt', noop: true, verbose: true)
  #     FileUtils.touch(['src0.txt', 'src0.dat'], noop: true, verbose: true)
  #     FileUtils.touch(path, noop: true, verbose: true)
  #
  #   Output:
  #
  #     touch src0.txt
  #     touch src0.txt src0.dat
  #     touch src0.txt
  #
  # Related: FileUtils.uptodate?.
  #
  def touch(list, noop: nil, verbose: nil, mtime: nil, nocreate: nil)
    list = fu_list(list)
    t = mtime
    if verbose
      fu_output_message "touch #{nocreate ? '-c ' : ''}#{t ? t.strftime('-t %Y%m%d%H%M.%S ') : ''}#{list.join ' '}"
    end
    return if noop
    list.each do |path|
      created = nocreate
      begin
        File.utime(t, t, path)
      rescue Errno::ENOENT
        raise if created
        File.open(path, 'a') {
          ;
        }
        created = true
        retry if t
      end
    end
  end
  module_function :touch

  private

  module StreamUtils_
    private

    case (defined?(::RbConfig) ? ::RbConfig::CONFIG['host_os'] : ::RUBY_PLATFORM)
    when /mswin|mingw/
      def fu_windows?; true end
    else
      def fu_windows?; false end
    end

    def fu_copy_stream0(src, dest, blksize = nil)   #:nodoc:
      IO.copy_stream(src, dest)
    end

    def fu_stream_blksize(*streams)
      streams.each do |s|
        next unless s.respond_to?(:stat)
        size = fu_blksize(s.stat)
        return size if size
      end
      fu_default_blksize()
    end

    def fu_blksize(st)
      s = st.blksize
      return nil unless s
      return nil if s == 0
      s
    end

    def fu_default_blksize
      1024
    end
  end

  include StreamUtils_
  extend StreamUtils_

  class Entry_   #:nodoc: internal use only
    include StreamUtils_

    def initialize(a, b = nil, deref = false)
      @prefix = @rel = @path = nil
      if b
        @prefix = a
        @rel = b
      else
        @path = a
      end
      @deref = deref
      @stat = nil
      @lstat = nil
    end

    def inspect
      "\#<#{self.class} #{path()}>"
    end

    def path
      if @path
        File.path(@path)
      else
        join(@prefix, @rel)
      end
    end

    def prefix
      @prefix || @path
    end

    def rel
      @rel
    end

    def dereference?
      @deref
    end

    def exist?
      begin
        lstat
        true
      rescue Errno::ENOENT
        false
      end
    end

    def file?
      s = lstat!
      s and s.file?
    end

    def directory?
      s = lstat!
      s and s.directory?
    end

    def symlink?
      s = lstat!
      s and s.symlink?
    end

    def chardev?
      s = lstat!
      s and s.chardev?
    end

    def blockdev?
      s = lstat!
      s and s.blockdev?
    end

    def socket?
      s = lstat!
      s and s.socket?
    end

    def pipe?
      s = lstat!
      s and s.pipe?
    end

    S_IF_DOOR = 0xD000

    def door?
      s = lstat!
      s and (s.mode & 0xF000 == S_IF_DOOR)
    end

    def entries
      opts = {}
      opts[:encoding] = fu_windows? ? ::Encoding::UTF_8 : path.encoding

      files = Dir.children(path, **opts)

      untaint = RUBY_VERSION < '2.7'
      files.map {|n| Entry_.new(prefix(), join(rel(), untaint ? n.untaint : n)) }
    end

    def stat
      return @stat if @stat
      if lstat() and lstat().symlink?
        @stat = File.stat(path())
      else
        @stat = lstat()
      end
      @stat
    end

    def stat!
      return @stat if @stat
      if lstat! and lstat!.symlink?
        @stat = File.stat(path())
      else
        @stat = lstat!
      end
      @stat
    rescue SystemCallError
      nil
    end

    def lstat
      if dereference?
        @lstat ||= File.stat(path())
      else
        @lstat ||= File.lstat(path())
      end
    end

    def lstat!
      lstat()
    rescue SystemCallError
      nil
    end

    def chmod(mode)
      if symlink?
        File.lchmod mode, path() if have_lchmod?
      else
        File.chmod mode, path()
      end
    rescue Errno::EOPNOTSUPP
    end

    def chown(uid, gid)
      if symlink?
        File.lchown uid, gid, path() if have_lchown?
      else
        File.chown uid, gid, path()
      end
    end

    def link(dest)
      case
      when directory?
        if !File.exist?(dest) and descendant_directory?(dest, path)
          raise ArgumentError, "cannot link directory %s to itself %s" % [path, dest]
        end
        begin
          Dir.mkdir dest
        rescue
          raise unless File.directory?(dest)
        end
      else
        File.link path(), dest
      end
    end

    def copy(dest)
      lstat
      case
      when file?
        copy_file dest
      when directory?
        if !File.exist?(dest) and descendant_directory?(dest, path)
          raise ArgumentError, "cannot copy directory %s to itself %s" % [path, dest]
        end
        begin
          Dir.mkdir dest
        rescue
          raise unless File.directory?(dest)
        end
      when symlink?
        File.symlink File.readlink(path()), dest
      when chardev?, blockdev?
        raise "cannot handle device file"
      when socket?
        begin
          require 'socket'
        rescue LoadError
          raise "cannot handle socket"
        else
          raise "cannot handle socket" unless defined?(UNIXServer)
        end
        UNIXServer.new(dest).close
        File.chmod lstat().mode, dest
      when pipe?
        raise "cannot handle FIFO" unless File.respond_to?(:mkfifo)
        File.mkfifo dest, lstat().mode
      when door?
        raise "cannot handle door: #{path()}"
      else
        raise "unknown file type: #{path()}"
      end
    end

    def copy_file(dest)
      File.open(path()) do |s|
        File.open(dest, 'wb', s.stat.mode) do |f|
          IO.copy_stream(s, f)
        end
      end
    end

    def copy_metadata(path)
      st = lstat()
      if !st.symlink?
        File.utime st.atime, st.mtime, path
      end
      mode = st.mode
      begin
        if st.symlink?
          begin
            File.lchown st.uid, st.gid, path
          rescue NotImplementedError
          end
        else
          File.chown st.uid, st.gid, path
        end
      rescue Errno::EPERM, Errno::EACCES
        # clear setuid/setgid
        mode &= 01777
      end
      if st.symlink?
        begin
          File.lchmod mode, path
        rescue NotImplementedError, Errno::EOPNOTSUPP
        end
      else
        File.chmod mode, path
      end
    end

    def remove
      if directory?
        remove_dir1
      else
        remove_file
      end
    end

    def remove_dir1
      platform_support {
        Dir.rmdir path().chomp(?/)
      }
    end

    def remove_file
      platform_support {
        File.unlink path
      }
    end

    def platform_support
      return yield unless fu_windows?
      first_time_p = true
      begin
        yield
      rescue Errno::ENOENT
        raise
      rescue => err
        if first_time_p
          first_time_p = false
          begin
            File.chmod 0700, path()   # Windows does not have symlink
            retry
          rescue SystemCallError
          end
        end
        raise err
      end
    end

    def preorder_traverse
      stack = [self]
      while ent = stack.pop
        yield ent
        stack.concat ent.entries.reverse if ent.directory?
      end
    end

    alias traverse preorder_traverse

    def postorder_traverse
      if directory?
        begin
          children = entries()
        rescue Errno::EACCES
          # Failed to get the list of children.
          # Assuming there is no children, try to process the parent directory.
          yield self
          return
        end

        children.each do |ent|
          ent.postorder_traverse do |e|
            yield e
          end
        end
      end
      yield self
    end

    def wrap_traverse(pre, post)
      pre.call self
      if directory?
        entries.each do |ent|
          ent.wrap_traverse pre, post
        end
      end
      post.call self
    end

    private

    @@fileutils_rb_have_lchmod = nil

    def have_lchmod?
      # This is not MT-safe, but it does not matter.
      if @@fileutils_rb_have_lchmod == nil
        @@fileutils_rb_have_lchmod = check_have_lchmod?
      end
      @@fileutils_rb_have_lchmod
    end

    def check_have_lchmod?
      return false unless File.respond_to?(:lchmod)
      File.lchmod 0
      return true
    rescue NotImplementedError
      return false
    end

    @@fileutils_rb_have_lchown = nil

    def have_lchown?
      # This is not MT-safe, but it does not matter.
      if @@fileutils_rb_have_lchown == nil
        @@fileutils_rb_have_lchown = check_have_lchown?
      end
      @@fileutils_rb_have_lchown
    end

    def check_have_lchown?
      return false unless File.respond_to?(:lchown)
      File.lchown nil, nil
      return true
    rescue NotImplementedError
      return false
    end

    def join(dir, base)
      return File.path(dir) if not base or base == '.'
      return File.path(base) if not dir or dir == '.'
      begin
        File.join(dir, base)
      rescue EncodingError
        if fu_windows?
          File.join(dir.encode(::Encoding::UTF_8), base.encode(::Encoding::UTF_8))
        else
          raise
        end
      end
    end

    if File::ALT_SEPARATOR
      DIRECTORY_TERM = "(?=[/#{Regexp.quote(File::ALT_SEPARATOR)}]|\\z)"
    else
      DIRECTORY_TERM = "(?=/|\\z)"
    end

    def descendant_directory?(descendant, ascendant)
      if File::FNM_SYSCASE.nonzero?
        File.expand_path(File.dirname(descendant)).casecmp(File.expand_path(ascendant)) == 0
      else
        File.expand_path(File.dirname(descendant)) == File.expand_path(ascendant)
      end
    end
  end   # class Entry_

  def fu_list(arg)   #:nodoc:
    [arg].flatten.map {|path| File.path(path) }
  end
  private_module_function :fu_list

  def fu_each_src_dest(src, dest)   #:nodoc:
    fu_each_src_dest0(src, dest) do |s, d|
      raise ArgumentError, "same file: #{s} and #{d}" if fu_same?(s, d)
      yield s, d
    end
  end
  private_module_function :fu_each_src_dest

  def fu_each_src_dest0(src, dest)   #:nodoc:
    if tmp = Array.try_convert(src)
      tmp.each do |s|
        s = File.path(s)
        yield s, File.join(dest, File.basename(s))
      end
    else
      src = File.path(src)
      if File.directory?(dest)
        yield src, File.join(dest, File.basename(src))
      else
        yield src, File.path(dest)
      end
    end
  end
  private_module_function :fu_each_src_dest0

  def fu_same?(a, b)   #:nodoc:
    File.identical?(a, b)
  end
  private_module_function :fu_same?

  def fu_output_message(msg)   #:nodoc:
    output = @fileutils_output if defined?(@fileutils_output)
    output ||= $stdout
    if defined?(@fileutils_label)
      msg = @fileutils_label + msg
    end
    output.puts msg
  end
  private_module_function :fu_output_message

  # This hash table holds command options.
  OPT_TABLE = {}    #:nodoc: internal use only
  (private_instance_methods & methods(false)).inject(OPT_TABLE) {|tbl, name|
    (tbl[name.to_s] = instance_method(name).parameters).map! {|t, n| n if t == :key}.compact!
    tbl
  }

  public

  # Returns an array of the string names of \FileUtils methods
  # that accept one or more keyword arguments:
  #
  #   FileUtils.commands.sort.take(3) # => ["cd", "chdir", "chmod"]
  #
  def self.commands
    OPT_TABLE.keys
  end

  # Returns an array of the string keyword names:
  #
  #   FileUtils.options.take(3) # => ["noop", "verbose", "force"]
  #
  def self.options
    OPT_TABLE.values.flatten.uniq.map {|sym| sym.to_s }
  end

  # Returns +true+ if method +mid+ accepts the given option +opt+, +false+ otherwise;
  # the arguments may be strings or symbols:
  #
  #   FileUtils.have_option?(:chmod, :noop) # => true
  #   FileUtils.have_option?('chmod', 'secure') # => false
  #
  def self.have_option?(mid, opt)
    li = OPT_TABLE[mid.to_s] or raise ArgumentError, "no such method: #{mid}"
    li.include?(opt)
  end

  # Returns an array of the string keyword name for method +mid+;
  # the argument may be a string or a symbol:
  #
  #   FileUtils.options_of(:rm) # => ["force", "noop", "verbose"]
  #   FileUtils.options_of('mv') # => ["force", "noop", "verbose", "secure"]
  #
  def self.options_of(mid)
    OPT_TABLE[mid.to_s].map {|sym| sym.to_s }
  end

  # Returns an array of the string method names of the methods
  # that accept the given keyword option +opt+;
  # the argument must be a symbol:
  #
  #   FileUtils.collect_method(:preserve) # => ["cp", "copy", "cp_r", "install"]
  #
  def self.collect_method(opt)
    OPT_TABLE.keys.select {|m| OPT_TABLE[m].include?(opt) }
  end

  private

  LOW_METHODS = singleton_methods(false) - collect_method(:noop).map(&:intern) # :nodoc:
  module LowMethods # :nodoc: internal use only
    private
    def _do_nothing(*)end
    ::FileUtils::LOW_METHODS.map {|name| alias_method name, :_do_nothing}
  end

  METHODS = singleton_methods() - [:private_module_function,                  # :nodoc:
      :commands, :options, :have_option?, :options_of, :collect_method]

  #
  # This module has all methods of FileUtils module, but it outputs messages
  # before acting.  This equates to passing the <tt>:verbose</tt> flag to
  # methods in FileUtils.
  #
  module Verbose
    include FileUtils
    names = ::FileUtils.collect_method(:verbose)
    names.each do |name|
      module_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def #{name}(*args, **options)
          super(*args, **options, verbose: true)
        end
      EOS
    end
    private(*names)
    extend self
    class << self
      public(*::FileUtils::METHODS)
    end
  end

  #
  # This module has all methods of FileUtils module, but never changes
  # files/directories.  This equates to passing the <tt>:noop</tt> flag
  # to methods in FileUtils.
  #
  module NoWrite
    include FileUtils
    include LowMethods
    names = ::FileUtils.collect_method(:noop)
    names.each do |name|
      module_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def #{name}(*args, **options)
          super(*args, **options, noop: true)
        end
      EOS
    end
    private(*names)
    extend self
    class << self
      public(*::FileUtils::METHODS)
    end
  end

  #
  # This module has all methods of FileUtils module, but never changes
  # files/directories, with printing message before acting.
  # This equates to passing the <tt>:noop</tt> and <tt>:verbose</tt> flag
  # to methods in FileUtils.
  #
  module DryRun
    include FileUtils
    include LowMethods
    names = ::FileUtils.collect_method(:noop)
    names.each do |name|
      module_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def #{name}(*args, **options)
          super(*args, **options, noop: true, verbose: true)
        end
      EOS
    end
    private(*names)
    extend self
    class << self
      public(*::FileUtils::METHODS)
    end
  end

end