Bash Perl正则表达式无法正确转义

Question

I have this command:

grep -PoRn '(?!.+?\.trigger[\(\s]+[\'\"])([a-zA-Z\:]+)(?>![\'\"])' .

But it throws up this:

-bash: ![\'\"]: event not found

Why? I have single quotes around my regex; I'm using -P for perl, I have escaped my single and double quotes, but nae luck.

Bash version is 4.2.25(1)-release on Ubuntu.

Any ideas? Cheers!

Answer 1

This is happening because history expansion happens inside single quotes.

You can get around this by using the $'' format:

grep -PoRn $'(?!.+?\.trigger[\(\s]+[\'\"])([a-zA-Z\:]+)(?>![\'\"])' .

From the bash man page:

   Words of the form $'string' are treated specially.  The word expands to
   string,  with backslash-escaped characters replaced as specified by the
   ANSI C standard.  Backslash escape sequences, if present,  are  decoded
   as follows:
          \a     alert (bell)
          \b     backspace
          \e
          \E     an escape character
          \f     form feed
          \n     new line
          \r     carriage return
          \t     horizontal tab
          \v     vertical tab
          \\     backslash
          \'     single quote
          \"     double quote
          \nnn   the  eight-bit  character  whose value is the octal value
                 nnn (one to three digits)
          \xHH   the eight-bit character whose value  is  the  hexadecimal
                 value HH (one or two hex digits)
          \uHHHH the  Unicode (ISO/IEC 10646) character whose value is the
                 hexadecimal value HHHH (one to four hex digits)
          \UHHHHHHHH
                 the Unicode (ISO/IEC 10646) character whose value is  the
                 hexadecimal value HHHHHHHH (one to eight hex digits)
          \cx    a control-x character

Answer 2

The ! is being treated as the beginning of a history expansion. You can turn this feature off temporarily with

set +H  # Turn history expansion off
grep -PoRn '(?!.+?\.trigger[\(\s]+[\'\"])([a-zA-Z\:]+)(?>![\'\"])' .
set -H  # Turn history expansion back on

Rather than turning it off and on unconditionally, you can check the $- parameter to see if the H option is set:

[[ $- = *H* ]]; hist_on=$?   # Is history expansion enabled?
(( hist_on )) && set +H      # Turn it off if it is
grep ...
(( hist_on )) && set -H      # Turn it back on if it was

If you are able to run your command in a subshell, you can just turn history expansion off for the subshell; the original setting in the current shell (on or off) will be unchanged.

( set +H; grep ... )