grep中的转义字符 [英] Escape characters in grep

问题描述

我对于在grep的正则表达式中需要多少个反斜杠来逃避交替运算符|感到有些困惑.这个

I'm a little confused about how many backslashes are needed to escape the alternation operator | in regular expressions for grep. This

echo abcdef | grep -e"def|zzz"

不输出任何内容，因为grep不在扩展的正则表达式模式下.使用一个反斜杠进行转义，

outputs nothing, because grep is not in extended regex mode. Escaping with one backslash works,

echo abcdef | grep -e"def\|zzz"

打印abcdef.更令人惊讶的是，使用2个反斜杠转义也可以，

prints abcdef. More surprisingly, escaping with 2 backslashes also works,

echo abcdef | grep -e"def\\|zzz"

打印abcdef.用三个反斜杠转义失败，

prints abcdef. Escaping with three backslashes fails,

echo abcdef | grep -e"def\\\|zzz"

不打印任何内容.

有人有解释吗，特别是在2反斜杠的情况下?

Does anyone have an explanation, especially for the 2-backslash case ?

使用此简单的参数打印程序

Using this simple argument-printing program,

void main(int argc, char** argv)
{
    for (int i = 0; i < argc; i++)
        printf("Arg %d: %s\n", i, argv[i]);
}

我研究了我的shell用上面的命令行做什么:

I investigated what my shell does with the command lines above :

-e"def|zzz"变为-edef|zzz

-e"def\|zzz"变为-edef\|zzz

-e"def\\|zzz"变为-edef\\|zzz

-e"def\\\|zzz"变为-edef\\\|zzz

因此，所有双引号都将被删除，并且反斜杠和竖线不会被外壳程序更改.我怀疑grep本身对文字字符串\\|做了特殊的事情.

So all double-quotes are removed and the backslashes and pipes are not altered by the shell. I suspect grep itself does something special with the literal string \\|.

推荐答案

小写的-e选项用于表示多个搜索操作.暗示着这种交替:

The lowercase -e option is used to express multiple search operations. The alternation is implied:

$ echo abcdef | grep -e 'def' -e'zzz'
abcdef
$ echo abczzz | grep -e 'def' -e'zzz'
abczzz

或者，您可以将大号-E选项用于扩展的正则表达式表示法:

Alternatively, you can use the upper -E option for extended regular expression notation:

$ echo abcdef | grep -E 'def|zzz'
abcdef

我相信这可以直接解决您的问题(使用-e进行替换或使用-E进行扩展的正则表达式表示法).希望这会有所帮助:-)

I believe this solves you problem directly (either using -e for alternation or -E for extended regex notation). Hope this helps :-)

FWIW，反斜杠的问题是|对于bash具有特殊含义，除非使用单引号，否则必须对其进行转义.这是有关引用和转义规则以及常见陷阱的资源: http://wiki.bash- hackers.org/syntax/quoting

FWIW, the issue with the backslashes is that | has special meaning to bash and needs to be escaped unless it is in single quotes. Here is a resource on quoting and escaping rules and the common pitfalls: http://wiki.bash-hackers.org/syntax/quoting

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