Grep syntax error with correct regex

Question

I've created a regex which I need to run with grep, I'm pretty sure the regex is fine as it works with online regex tools, however when I run

grep -r -P -o -h '(?<=(?<!def )my_method )(["'])(?:(?=(\\?))\2.)*?\1'

I get the error Syntax error: ")" unexpected.

score 10 · Accepted Answer · edited Apr 03 '17 at 14:20

10

Your regular expression is quoted with single quotes, but it also contains a single quote.

The single quote in ["'] needs to be escaped, or it will signal the end of the quoted string to the shell.

This will fix it:

grep -r -P -o -h '(?<=(?<!def )my_method )(["'\''])(?:(?=(\\?))\2.)*?\1'
#                                            ^^^^

With ["'\''], the first ' ends the first part of the string, the \' inserts a literal single quote, and the last ' starts a new single quoted string that will be concatenated with the previous bits. Only the middle single quote will end up in the regular expression itself, the other two will be removed by the shell.

edited Apr 03 '17 at 14:20

fedorqui

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answered Apr 03 '17 at 12:11

Kusalananda

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Nice Tricky method. Alternative : `(["\x27])` will work fine (replacing the single quote with it's ascii code) – George Vasiliou Apr 03 '17 at 12:23
@GeorgeVasiliou That's also a good solution, yes. `\x27` is as many characters as `'\''`. – Kusalananda Apr 03 '17 at 12:24
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Though `'\''` is transferable to other non-regex situations whereas `\x27` is not. – Muzer Apr 03 '17 at 14:41

score 5 · Answer 2 · edited Apr 13 '17 at 12:37

5

As @Kusalananda explained, the problem is the ' inside the regex. A simple solution is to use " for the regex since " can be escaped even inside a "-quoted string, unlike ' which cannot be escaped inside a '-quoted string:

grep -rPoh "(?<=(?<!def )my_method )([\"'])(?:(?=(\\?))\2.)*?\1"

edited Apr 13 '17 at 12:37

Community

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answered Apr 03 '17 at 12:39

terdon

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Grep syntax error with correct regex

2 Answers2