regexp with perl, ungreedy not working as expected

Question

Could somebody explain to me, why this is not working:

# echo '"Hello,1" "Hello,2" "Hello,3"' | perl -pe 's/".+?,3"/1/'
1

or

# echo '"Hello,1" "Hello,2" "Hello,3"' | perl -pe 's/".+?,2"/1/'
1 "Hello,3"

My intention was to replace/find only "Hello,3"/"Hello,2", but It seems that the non-greedy modifier (or my brain) is not working as expected.

Regex engine matches the string from left to right, the `"` matched the first `"`, and `.+?` did its job correctly, matched up to the first `,3"`. What is the expected output, BTW? — Wiktor Stribiżew, Nov 25 '16 at 09:21
Could you please clarify what the expected output is? `"Hello,1" "Hello,2" 1`? — Wiktor Stribiżew, Nov 25 '16 at 09:24

score 2 · Answer 1 · answered Nov 25 '16 at 09:30

I think you're misunderstanding regular expressions, but actually I'd probably suggest tackling this one a bit differently. If you've a sequence of words to manipulate, I'd suggest using split/join/map to do the manipulation.

I think it scales better, and doesn't trip over on clarity problems with where the pattern matching boundaries lie.

Something like this:

my $str = '"Hello,1" "Hello,2" "Hello,3"';

$str = join ( " ", map { s/Hello,[23]/1/r } split ( " ", $str ) );
print $str;

Or as a one liner:

perl -ape "/Hello/ and $_ = join ' ', map { s/Hello,[23]/1/r } @F"

score 1 · Answer 2 · edited Nov 25 '16 at 10:02

1

Try this

/"[^"]+,3"/

instead. https://regex101.com/r/4rXN4z/1

edited Nov 25 '16 at 10:02

ceving

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answered Nov 25 '16 at 09:24

Fallenhero

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Some narrative would help a lot here. – Borodin Nov 25 '16 at 09:55
Well it's better, but still a bit cheap – Borodin Nov 25 '16 at 14:43

regexp with perl, ungreedy not working as expected

2 Answers2