bash 正则表达式带引号？

Question

以下代码

number=1
if [[ $number =~ [0-9] ]]
then
  echo matched
fi

有效。但是，如果我尝试在正则表达式中使用引号，它会停止：

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

我也试过"\[0-9\]"。我错过了什么？

有趣的是，bash advanced scripting guide 建议这应该可行。

Bash 版本 3.2.39。

Answer 1

已更改between 3.1 and 3.2。猜猜高级指南需要更新。

这是对新产品的简要描述 自 bash-3.2 以来添加的功能 发布 bash-3.1。一如既往， 手册页（doc/bash.1）是这个地方 寻找完整的描述。

1. Bash 中的新功能

剪辑

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。

遗憾的是，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，否则这会破坏使用脚本的现有引用。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

Answer 2

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

没有 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

Answer 3

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

字符串匹配和正则匹配的一些例子

    $ 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

Answer 4

正如其他答案中提到的，将正则表达式放在变量中是实现不同bash 版本兼容的一般方法。您也可以使用此解决方法来实现相同的目的，同时将您的正则表达式保持在条件表达式中：

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