Bash – Why doesn’t this regex work

bashregular expression

I want to look at the output of git status -s to determine whether there are any untracked files in the tree. I tried the following test, but the regex doesn't match. Why not?

$ git status -s
## master
 M updated-file
?? new-file
$ [[ $(git status -s) =~ ^\?\? ]] || echo "no match"
no match

I'd also like to be able to test for added/modified/deleted files in the same way. I'd normally just use something like ^\s*[AMD] for this purpose, but this doesn't work either. What gives?

Best Answer

You're matching against the whole string, not each line of the string, as such you're really testing against ## in that regex.

grep is a better choice for this:

if ! git status -s | grep -q '^??'; then
    echo "no match"
fi

As requested, you can do the same for added/modified/deleted:

git status -s | grep '^ *[AMD]'

You might also want to look into git status --porcelain (an option that first appeared in 1.7.0), which is more oriented towards parsing.

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I'm not sure why Perl isn't acceptable here. On the inputs you provided, this line gives the output you asked for:

perl -0777p -e 's/.* > (.*) joined the channel\.\n(((?!.* \1 (was kicked from channel\.|was banned from channel\.)\n).*\n)+?.*\1 disconnected)/\2/mg' irc.txt

The -e argument is exactly the first argument to your magicregextool except that I added the /mg regex modifier. This may not be "unmodified" but it doesn't seem unreasonable either. If you don't want to type in the whole line, how about this script as magicregextool:

#!/usr/bin/perl -0777p
BEGIN { $::arg = shift @ARGV; }
eval $arg;

Or even:

#!/bin/sh
perl -0777pe $*

Then you just type:

magicregextool 's/.* > (.*) joined the channel\.\n(((?!.* \1 (was kicked from channel\.|was banned from channel\.)\n).*\n)+?.*\1 disconnected)/\2/mg' irc.txt

Which is the same as your sample (again other than adding the /mg modifier).

An additional benefit to this is that if you are running multiple related search/replace operations on each file, you can put them together in the same script:

#!/usr/bin/perl -0777p
s/.* > (.*) joined the channel\.\n(((?!.* \1 (was kicked from channel\.|was banned from channel\.)\n).*\n)+?.*\1 disconnected)/\2/mg;
s/(some other\n)matched text/\1/mg;

Best Answer

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