How do you “debug” a regular expression with sed?

Question

I\'m trying to use a regexp using sed. I\'ve tested my regex with kiki, a gnome application to test regexpd, and it works in kiki.

date: 2010-10-29          


        

Answer 1

My version of sed doesn't like the {11} bit. Processing the line with:

sed 's/author: [0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9];//g'

works fine.

And the way I debug it is exactly what I did here. I just constructed a command:

echo 'X author: 00000000000; X' | sed ...

and removed the more advanced regex things one at a time:

• used instead of \s, didn't fix it.
• replaced [0-9]{11} with 11 copies of [0-9], that worked.

It pretty much had to be one of those since I've used every other feature of your regex before with sed successfully.

But, in fact, this will actually work without the hideous 11 copies of [0-9], you just have to escape the braces [0-9]\{11\}. I have to admit I didn't get around to trying that since it worked okay with the multiples and I generally don't concern myself too much with brevity in sed since I tend to use it more for quick'n'dirty jobs :-)

But the brace method is a lot more concise and adaptable and it's good to know how to do it.