[WORKAROUND] Lookbehind and lookahead possible?

[sergeevabc]

I/O

echo Saving to: 'hello.sql' | sift --only-matching (?<=').+(?=')
The filename, directory name, or volume label syntax is incorrect.

Expected

hello.sql

It seems error occurs because cmd.exe fails to process special chars, right?

However the following piece confuses me whether issue is about cmd.exe of Sift itself.

echo Saving to: 'hello.sql' | sift --only-matching -e "(?<=').+(?=')"
Error: cannot parse pattern: error parsing regexp: invalid or unsupported Perl syntax: `(?<`

[sergeevabc]

Err… Hello?

[svent]

You are right, the first example does not work due to escaping problems. The second example is "correct": sift does not support lookbehind/lookahead assertions. The task of extracting the filename is possible though:

echo Saving to: 'hello.sql' | sift "'(.+)'" --replace "$1"
hello.sql

[sergeevabc]

Thank you for a workaround, Sven. Should I rename this issue to “Implement support of lookbehind/lookahead”?

[svent]

That limitation comes from the Go RegEx engine that I use in sift, so unfortunately it cannot easily be fixed.

[sergeevabc]

Oh, it makes life so harder. For example, (\w+)(\.\w+)+(?!.*(\w+)(\.\w+)+) to get a filename from URL does not work. More or less workaround is [^\/?#]*\.[^\/?#]*(\?.*)?(\#.*)?$.