How can I properly escape this regex in bash?

Question

I'm trying to run grep with the following regex:

(?<!key:)(?<!orKey:)(?<!isEqualToString:)\@\"[A-Za-z0-9]*\"

First try:

$ grep -r -n  -H -E (?<!key:)(?<!orKey:)(?<!isEqualToString:)\@\"[A-Za-z0-9]*\" ./
    -bash: !key: event not found

Ok, so I need to escape the "!"s...

$ grep -r -n  -H -E (?<\!key:)(?<\!orKey:)(?<\!isEqualToString:)\@\"[A-Za-z0-9]*\" ./
    -bash: syntax error near unexpected token `('

Ok, so I need to escape the "("s...

$ grep -r -n  -H -E \(?<\!key:\)\(?<\!orKey:\)\(?<\!isEqualToString:\)\@\"[A-Za-z0-9]*\" ./
    -bash: !key:)(?: No such file or directory

Ok, so I need to quote the string?

$ grep -r -n  -H -E '\(?<\!key:\)\(?<\!orKey:\)\(?<\!isEqualToString:\)\@\"[A-Za-z0-9]*\"' ./

Returns no results... but I tried a simpler regex which doesn't have the negative-look-behind assertions, and it ran fine... I also used TextWrangler with this regex and it does work, so I can only assume I'm doing something wrong on the command line here.

EDIT:

If I use the -p option:

$ grep -r -n  -H -E -P '\(?<\!key:\)\(?<\!orKey:\)\(?<\!isEqualToString:\)\@\"[A-Za-z0-9]*\"' ./
grep: conflicting matchers specified

An example of file contents which should match:

NSString * foo = @"bar";

An example of file contents which should NOT match:

return [someDictonary objectForKey:@"foo"];

Answer 1

At the core of it you need to quote the entire string with ''. (If you enclose with "" the ! will give you grief). Then you only need to escape internal ' within your regex (if any).

Also you want -P (perl) instead of -E (egrep) regex.

grep -r -n -H -P '(?<!key:)(?<!orKey:)(?<!isEqualToString:)\@\"[A-Za-z0-9]*\"' ./

Answer 2

try using the -P option which will interpret the regex as a perl regex. Also if you provide some example input and output it would help in getting an answer.

Answer 3

' quoting works perfectly as long as there are no ' in your expression. And you don't have any, so that should be fine.

If you are really paranoid about quoting, put the expression in a file and use grep -f FILENAME instead, so that it reads the regex from the file.

But the real issue might be that you need to specify grep -P to explicitly ask for the Perl regular expression support.

Answer 4

It works fine, just avoid using conflicting options. -

[jaypal:~/Temp] cat filename
NSString * foo = @"bar";
return [someDictonary objectForKey:@"foo"];

[jaypal:~/Temp] grep -P '(?<!key:)(?<!orKey:)(?<!isEqualToString:)\@\"[A-Za-z0-9]*\"' filename
NSString * foo = @"bar";