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

If you want to debug a sed command, you can use the w (write) command to dump which lines sed has matched to a file.

From sed manpages:

Commands which accept address ranges

(...)

w filename

Write the current pattern space to filename.

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Applying to your question

Let's use a file named sed_dump.txt as the sed dump file.

1) Generate the sed dump:

sed "/author:\s[0-9]{11};/w sed_dump.txt" /tmp/test_regex.txt

2) Check file sed_dump.txt contents:

cat sed_dump.txt

Output:

It's empty...

3) Trying to escape '{' regex control character:

sed "/author:\s[0-9]\{11\};/w sed_dump.txt" /tmp/test_regex.txt

4) Check file sed_dump.txt contents:

cat sed_dump.txt

Output:

date: 2010-10-29 14:46:33 -0200; author: 00000000000; state: Exp; lines: +5 -2; commitid: bvEcb00aPyqal6Uu;

Conclusion

In step 4), a line has been matched, this means that sed matched your pattern in that line. It does not guarantee the correct answer, but it's a way of debugging using sed itself.