如何在Bash中将字符串转换为小写? [英] How to convert a string to lower case in Bash?

问题描述

bash 的方法中是否有一种方法可以转换字符串变成小写字符串?

Is there a way in bash to convert a string into a lower case string?

例如，如果我有:

a="Hi all"

我想将其转换为:

"hi all"

推荐答案

有多种方法:

$ echo "$a" | tr '[:upper:]' '[:lower:]'
hi all

AWK

$ echo "$a" | awk '{print tolower($0)}'
hi all

非POSIX

您可能会遇到以下示例的可移植性问题:

Non-POSIX

You may run into portability issues with the following examples:

$ echo "${a,,}"
hi all

sed

$ echo "$a" | sed -e 's/\(.*\)/\L\1/'
hi all
# this also works:
$ sed -e 's/\(.*\)/\L\1/' <<< "$a"
hi all

Perl

$ echo "$a" | perl -ne 'print lc'
hi all

Bash

lc(){
    case "$1" in
        [A-Z])
        n=$(printf "%d" "'$1")
        n=$((n+32))
        printf \\$(printf "%o" "$n")
        ;;
        *)
        printf "%s" "$1"
        ;;
    esac
}
word="I Love Bash"
for((i=0;i<${#word};i++))
do
    ch="${word:$i:1}"
    lc "$ch"
done

注意:YMMV在这一点上.即使使用shopt -u nocasematch;，它也对我不起作用(GNU bash版本4.2.46和4.0.33(具有相同的行为2.05b.0，但未实现大小写匹配)).取消设置nocasematch会导致[[-"fooBaR" =="FOObar"]]奇怪地匹配[B-z]内的情况，但[A-Z]不正确地匹配了[b-z]. Bash被双重负数("uncasematch")弄糊涂了！ :-)

Note: YMMV on this one. Doesn't work for me (GNU bash version 4.2.46 and 4.0.33 (and same behaviour 2.05b.0 but nocasematch is not implemented)) even with using shopt -u nocasematch;. Unsetting that nocasematch causes [[ "fooBaR" == "FOObar" ]] to match OK BUT inside case weirdly [b-z] are incorrectly matched by [A-Z]. Bash is confused by the double-negative ("unsetting nocasematch")! :-)

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