bash中有没有将字符串转换为小写字符串的方法？
例如，如果我有：
a="Hi all"
我想将其转换为：
"hi all"
当前回答
tr:
a="$(tr [A-Z] [a-z] <<< "$a")"
AWK:
{ print tolower($0) }
sed:
y/ABCDEFGHIJKLMNOPQRSTUVWXYZ/abcdefghijklmnopqrstuvwxyz/
其他回答
在zsh中：
echo $a:u
我爱你！
因此，我尝试对每个实用程序使用共识方法执行一些更新的基准测试，但我没有多次重复一个小集合，而是。。。
以UTF-8编码的多字节Unicode字符填充到边缘的1.85 GB.txt文件中，为了均衡I/O方面，同时还强制所有人使用LC_ALL=C，以确保公平竞争
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准确地说，bsd-sed和gnu-sed都相当平庸。我甚至不知道bsd sed在做什么，因为他们的xxhash不匹配python3是否试图使用Unicode字母大小写？（即使我已经强制设置了区域设置LC_ALL=C）tr是最极端的到目前为止，gnutr是最快的bsd tr非常残暴perl5比我拥有的任何awk变体都快，除非你可以使用mawk2一次加载整个文件，以便稍微超过perl5：2.935秒mawk2对每15秒3.081秒在awk中，gnu-gawk的速度最慢，中间是mawk 1.3.4，最快是mawk1.9.9.6：比gawk节省50%以上的时间.（我没有把时间浪费在无用的macosx nawk上）
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out9: 1.85GiB 0:00:03 [ 568MiB/s] [ 568MiB/s] [ <=> ]
in0: 1.85GiB 0:00:03 [ 568MiB/s] [ 568MiB/s] [============>] 100%
( pvE 0.1 in0 < "${m3t}" | LC_ALL=C mawk2 '{ print tolower($_) }' FS='^$'; )
mawk 1.9.9.6 (mawk2-beta)
3.07s user 0.66s system 111% cpu 3.348 total
85759a34df874966d096c6529dbfb9d5 stdin
out9: 1.85GiB 0:00:06 [ 297MiB/s] [ 297MiB/s] [ <=> ]
in0: 1.85GiB 0:00:06 [ 297MiB/s] [ 297MiB/s] [============>] 100%
( pvE 0.1 in0 < "${m3t}" | LC_ALL=C mawk '{ print tolower($_) }' FS='^$'; )
mawk 1.3.4
6.01s user 0.83s system 107% cpu 6.368 total
85759a34df874966d096c6529dbfb9d5 stdin
out9: 23.8MiB 0:00:00 [ 238MiB/s] [ 238MiB/s] [ <=> ]
in0: 1.85GiB 0:00:07 [ 244MiB/s] [ 244MiB/s] [============>] 100%
out9: 1.85GiB 0:00:07 [ 244MiB/s] [ 244MiB/s] [ <=> ]
( pvE 0.1 in0 < "${m3t}" | LC_ALL=C gawk -be '{ print tolower($_) }' FS='^$';
GNU Awk 5.1.1, API: 3.1 (GNU MPFR 4.1.0, GNU MP 6.2.1)
7.49s user 0.78s system 106% cpu 7.763 total
85759a34df874966d096c6529dbfb9d5 stdin
out9: 1.85GiB 0:00:03 [ 616MiB/s] [ 616MiB/s] [ <=> ]
in0: 1.85GiB 0:00:03 [ 617MiB/s] [ 617MiB/s] [============>] 100%
( pvE 0.1 in0 < "${m3t}" | LC_ALL=C perl -ne 'print lc'; )
perl5 (revision 5 version 34 subversion 0)
2.70s user 0.85s system 115% cpu 3.081 total
85759a34df874966d096c6529dbfb9d5 stdin
out9: 1.85GiB 0:00:32 [57.4MiB/s] [57.4MiB/s] [ <=> ]
in0: 1.85GiB 0:00:32 [57.4MiB/s] [57.4MiB/s] [============>] 100%
( pvE 0.1 in0 < "${m3t}" | LC_ALL=C gsed 's/.*/\L&/'; ) # GNU-sed
gsed (GNU sed) 4.8
32.57s user 0.97s system 101% cpu 32.982 total
85759a34df874966d096c6529dbfb9d5 stdin
out9: 1.86GiB 0:00:38 [49.7MiB/s] [49.7MiB/s] [ <=> ]
in0: 1.85GiB 0:00:38 [49.4MiB/s] [49.4MiB/s] [============>] 100%
( pvE 0.1 in0 < "${m3t}" | LC_ALL=C sed 's/.*/\L&/'; ) # BSD-sed
37.94s user 0.86s system 101% cpu 38.318 total
d5e2d8487df1136db7c2334a238755c0 stdin
in0: 313MiB 0:00:00 [3.06GiB/s] [3.06GiB/s] [=====>] 16% ETA 0:00:00
out9: 1.85GiB 0:00:11 [ 166MiB/s] [ 166MiB/s] [ <=>]
in0: 1.85GiB 0:00:00 [3.31GiB/s] [3.31GiB/s] [============>] 100%
( pvE 0.1 in0 < "${m3t}" | LC_ALL=C python3 -c "print(open(0).read().lower()))
Python 3.9.12
9.04s user 2.18s system 98% cpu 11.403 total
7ddc0b5cbcfbbfac3c2b6da6731bd262 stdin
out9: 2.51MiB 0:00:00 [25.1MiB/s] [25.1MiB/s] [ <=> ]
in0: 1.85GiB 0:00:11 [ 171MiB/s] [ 171MiB/s] [============>] 100%
out9: 1.85GiB 0:00:11 [ 171MiB/s] [ 171MiB/s] [ <=> ]
( pvE 0.1 in0 < "${m3t}" | LC_ALL=C ruby -pe '$_.downcase!'; )
ruby 2.6.8p205 (2021-07-07 revision 67951) [universal.arm64e-darwin21]
10.46s user 1.23s system 105% cpu 11.073 total
85759a34df874966d096c6529dbfb9d5 stdin
in0: 1.85GiB 0:00:01 [1.01GiB/s] [1.01GiB/s] [============>] 100%
out9: 1.85GiB 0:00:01 [1.01GiB/s] [1.01GiB/s] [ <=> ]
( pvE 0.1 in0 < "${m3t}" | LC_ALL=C gtr '[A-Z]' '[a-z]'; ) # GNU-tr
gtr (GNU coreutils) 9.1
1.11s user 1.21s system 124% cpu 1.855 total
85759a34df874966d096c6529dbfb9d5 stdin
out9: 1.85GiB 0:01:19 [23.7MiB/s] [23.7MiB/s] [ <=> ]
in0: 1.85GiB 0:01:19 [23.7MiB/s] [23.7MiB/s] [============>] 100%
( pvE 0.1 in0 < "${m3t}" | LC_ALL=C tr '[A-Z]' '[a-z]'; ) # BSD-tr
78.94s user 1.50s system 100% cpu 1:19.67 total
85759a34df874966d096c6529dbfb9d5 stdin
( time ( pvE0 < "${m3t}" | LC_ALL=C gdd conv=lcase ) | pvE9 ) | xxh128sum | lgp3; sleep 3;
out9: 0.00 B 0:00:01 [0.00 B/s] [0.00 B/s] [<=> ]
in0: 1.85GiB 0:00:06 [ 295MiB/s] [ 295MiB/s] [============>] 100%
out9: 1.81GiB 0:00:06 [ 392MiB/s] [ 294MiB/s] [ <=> ]
3874110+1 records in
3874110+1 records out
out9: 1.85GiB 0:00:06 [ 295MiB/s] [ 295MiB/s] [ <=> ]
( pvE 0.1 in0 < "${m3t}" | LC_ALL=C gdd conv=lcase; ) # GNU-dd
gdd (coreutils) 9.1
1.93s user 4.35s system 97% cpu 6.413 total
85759a34df874966d096c6529dbfb9d5 stdin
% ( time ( pvE0 < "${m3t}" | LC_ALL=C dd conv=lcase ) | pvE9 ) | xxh128sum | lgp3; sleep 3;
out9: 36.9MiB 0:00:00 [ 368MiB/s] [ 368MiB/s] [ <=> ]
in0: 1.85GiB 0:00:04 [ 393MiB/s] [ 393MiB/s] [============>] 100%
out9: 1.85GiB 0:00:04 [ 393MiB/s] [ 393MiB/s] [ <=> ]
3874110+1 records in
3874110+1 records out
out9: 1.85GiB 0:00:04 [ 393MiB/s] [ 393MiB/s] [ <=> ]
( pvE 0.1 in0 < "${m3t}" | LC_ALL=C dd conv=lcase; ) # BSD-dd
1.92s user 4.24s system 127% cpu 4.817 total
85759a34df874966d096c6529dbfb9d5 stdin
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通过一次加载所有文件，并在单个函数调用中对所有1.85 GB执行tolower（），可以人为地使mawk2比perl5更快：：
( time ( pvE0 < "${m3t}" |
LC_ALL=C mawk2 '
BEGIN { FS = RS = "^$" }
END { print tolower($(ORS = "")) }'
) | pvE9 ) | xxh128sum| lgp3
in0: 1.85GiB 0:00:00 [3.35GiB/s] [3.35GiB/s] [============>] 100%
out9: 1.85GiB 0:00:02 [ 647MiB/s] [ 647MiB/s] [ <=> ]
( pvE 0.1 in0 < "${m3t}" | LC_ALL=C mawk2 ; )
1.39s user 1.31s system 91% cpu 2.935 total
85759a34df874966d096c6529dbfb9d5 stdin
echo "Hi All" | tr "[:upper:]" "[:lower:]"
对于Bash命令行，根据语言环境和国际字母，这可能会起作用（根据其他人的答案组合而成）：
$ echo "ABCÆØÅ" | python -c "print(open(0).read().lower())"
abcæøå
$ echo "ABCÆØÅ" | sed 's/./\L&/g'
abcæøå
$ export a="ABCÆØÅ" | echo "${a,,}"
abcæøå
尽管这些变化可能不起作用：
$ echo "ABCÆØÅ" | tr "[:upper:]" "[:lower:]"
abcÆØÅ
$ echo "ABCÆØÅ" | awk '{print tolower($1)}'
abcÆØÅ
$ echo "ABCÆØÅ" | perl -ne 'print lc'
abcÆØÅ
$ echo 'ABCÆØÅ' | dd conv=lcase 2> /dev/null
abcÆØÅ
简单的方法
echo "Hi all" | awk '{ print tolower($0); }'
