Dear Monks,

Perhaps I'm not seeing the obvious mistake in my regexp-code, but I think I found some strange behavior of the regexpr engine:

wine@localhost]$ perl -pe 's/(")[^\1]*\1/check/g'
"strings 1" "string 2" # input
check #output
[download]

I hope you'll agree this is wrong. It should yield: check check. If you transscribe the expression by removing the backreferences you get the normal behavior:

wine@localhost]$ perl -pe 's/"[^"]*"/check/g'
"string 1" "string 2"
check check
[download]

Using $1 yields:

wine@localhost]$ perl -pe 's/(")[^$1]*$1/check/g'
"string 1" "string 2"
Unmatched [ before HERE mark in regex m/(")[ << HERE ^]*/ at -e line 1
+, <> line 1.
[download]

This isn't related to the ". It doesn't work with normal alpha-characters either:

wine@localhost]$ perl -pe 's/(a)[^\1]*\1/check/g'
abbbba abbbbbbbba
check
[download]

Using a | helps if the two side differ:

# ("|'"'"') is a complex bash escape for ("|')

wine@localhost]$ perl -pe 's/("|'"'"')[^\1]*\1/check/g' 
"aaa" 'aaa'
check check
[download]

But if you use differt input it goes wrong again, and this should really not happen:

perl -pe 's/("|'"'"')[^\1]*\1/check/g'
"aaa" "aaa"
check
[download]

Can someone explain this behavior. (").*?\1 seems to work, but is not compliant with lets say sed, which seems to have the same problem:

wine@localhost]$ sed 's/\(a\)[^\1]*\1/check/g'
abbbba abbbbbbbba
check
[download]

Thank you in advance

wine

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