带引号的 bash 正则表达式？

它在 3.1 和 3.2 之间更改。猜猜高级指南需要更新。

这是对新事物的简要描述 bash-3.2 添加的功能自 发布 bash-3.1。与往常一样， 手册页（doc/bash.1）是这个地方 以查找完整的说明。

1. Bash 中的新增功能

剪 断

f.将字符串参数引用到 [[ 命令的 =~ 运算符现在强制 字符串匹配，与其他模式匹配运算符一样。

可悲的是，这将使用脚本破坏现有的报价，除非您有洞察力将模式存储在变量中并直接使用它们而不是正则表达式。下面的例子。

$ bash --version
GNU bash, version 3.2.39(1)-release (i486-pc-linux-gnu)
Copyright (C) 2007 Free Software Foundation, Inc.
$ number=2
$ if [[ $number =~ "[0-9]" ]]; then echo match; fi
$ if [[ $number =~ [0-9] ]]; then echo match; fi
match
$ re="[0-9]"
$ if [[ $number =~ $re ]]; then echo MATCH; fi
MATCH

$ bash --version
GNU bash, version 3.00.0(1)-release (i586-suse-linux)
Copyright (C) 2004 Free Software Foundation, Inc.
$ number=2
$ if [[ $number =~ "[0-9]" ]]; then echo match; fi
match
$ if [[ "$number" =~ [0-9] ]]; then echo match; fi
match

Bash 3.2 引入了一个兼容性选项 compat31，它将 bash 正则表达式引用行为恢复到 3.1

不带 compat31：

$ shopt -u compat31
$ shopt compat31
compat31        off
$ set -x
$ if [[ "9" =~ "[0-9]" ]]; then echo match; else echo no match; fi
+ [[ 9 =~ \[0-9] ]]
+ echo no match
no match

使用 compat31：

$ shopt -s compat31
+ shopt -s compat31
$ if [[ "9" =~ "[0-9]" ]]; then echo match; else echo no match; fi
+ [[ 9 =~ [0-9] ]]
+ echo match
match

补丁链接：http://ftp.gnu.org/gnu/bash/bash-3.2-patches/bash32-039

GNU bash，版本 4.2.25（1）-release （x86_64-pc-linux-gnu）

字符串匹配和正则表达式匹配的一些示例

    $ if [[ 234 =~ "[0-9]" ]]; then echo matches;  fi # string match
    $ 

    $ if [[ 234 =~ [0-9] ]]; then echo matches;  fi # regex natch 
    matches


    $ var="[0-9]"

    $ if [[ 234 =~ $var ]]; then echo matches;  fi # regex match
    matches


    $ if [[ 234 =~ "$var" ]]; then echo matches;  fi # string match after substituting $var as [0-9]

    $ if [[ 'rss$var919' =~ "$var" ]]; then echo matches;  fi   # string match after substituting $var as [0-9]

    $ if [[ 'rss$var919' =~ $var ]]; then echo matches;  fi # regex match after substituting $var as [0-9]
    matches


    $ if [[ "rss\$var919" =~ "$var" ]]; then echo matches;  fi # string match won't work

    $ if [[ "rss\\$var919" =~ "$var" ]]; then echo matches;  fi # string match won't work


    $ if [[ "rss'$var'""919" =~ "$var" ]]; then echo matches;  fi # $var is substituted on LHS & RHS and then string match happens 
    matches

    $ if [[ 'rss$var919' =~ "\$var" ]]; then echo matches;  fi # string match !
    matches



    $ if [[ 'rss$var919' =~ "$var" ]]; then echo matches;  fi # string match failed
    $ 

    $ if [[ 'rss$var919' =~ '$var' ]]; then echo matches;  fi # string match
    matches



    $ echo $var
    [0-9]

    $ 

    $ if [[ abc123def =~ "[0-9]" ]]; then echo matches;  fi

    $ if [[ abc123def =~ [0-9] ]]; then echo matches;  fi
    matches

    $ if [[ 'rss$var919' =~ '$var' ]]; then echo matches;  fi # string match due to single quotes on RHS $var matches $var
    matches


    $ if [[ 'rss$var919' =~ $var ]]; then echo matches;  fi # Regex match 
    matches
    $ if [[ 'rss$var' =~ $var ]]; then echo matches;  fi # Above e.g. really is regex match and not string match
    $


    $ if [[ 'rss$var919[0-9]' =~ "$var" ]]; then echo matches;  fi # string match RHS substituted and then matched
    matches

    $ if [[ 'rss$var919' =~ "'$var'" ]]; then echo matches;  fi # trying to string match '$var' fails


    $ if [[ '$var' =~ "'$var'" ]]; then echo matches;  fi # string match still fails as single quotes are omitted on RHS 

    $ if [[ \'$var\' =~ "'$var'" ]]; then echo matches;  fi # this string match works as single quotes are included now on RHS
    matches

正如其他答案中提到的，将正则表达式放在变量中是实现对不同 bash 版本的兼容性的通用方法。您也可以使用此解决方法来实现相同的目的，同时将正则表达式保留在条件表达式中：

$ number=1
$ if [[ $number =~ $(echo "[0-9]") ]]; then echo matched; fi
matched
$ 

使用局部变量的性能略好于使用命令替换。

对于较大的脚本或脚本集合，使用实用程序来防止不需要的局部变量污染代码并减少详细程度可能是有意义的。这似乎很有效：

# Bash's built-in regular expression matching requires the regular expression
# to be unqouted (see https://stackoverflow.com/q/218156), which makes it harder
# to use some special characters, e.g., the dollar sign.
# This wrapper works around the issue by using a local variable, which means the
# quotes are not passed on to the regex engine.
regex_match() {
  local string regex
  string="${1?}"
  regex="${2?}"
  # shellcheck disable=SC2046 `regex` is deliberately unquoted, see above.
  [[ "${string}" =~ ${regex} ]]
}

用法示例：

if regex_match "${number}" '[0-9]'; then
  echo matched
fi