Re^4: Use of uninitialized value $1

Yes, this is a nit ...

Regular expressions, love them though I do, consist in a vast collection of nits IMHO.

I'm not sure that [these variables keep their value] is true. I remember a node that fairly recently talked about this, but I couldn't find it ... What I remember is that a failed match could in some circumstances modify $1.

Now that you mention it, I seem to remember something along those lines myself. Unfortunately, my Super Search-fu is no better than yours, and I could come up with no pertinent node. Have to keep searching, searching... (Maybe it had to do with the match portion of s/// having the same effects on regex variables as m// does?)

Comment on Re^4: Use of uninitialized value $1 Select or Download Code

Replies are listed 'Best First'.
Re^5: Use of uninitialized value $1 by Marshall (Canon) on Aug 26, 2016 at 03:15 UTC
perlre says: NOTE: Failed matches in Perl do not reset the match variables, which makes it easier to write code that tests for a series of more specific cases and remembers the best match. However, we both remember something different about that. I hope some other Monk can point us in the right direction. Update: After some reflection, my memory recalls some situation where there were several capture groups, $1,$2,$3. Overall, the match failed, but the first part ($1) did match and change $1 although the rest of the expression $2,$3 didn't match and didn't change. This behavior was version specific. So, this is a cautionary note that despite what the doc says, there may be some "bite you" case out there that my super-search foo is not able to find.	[reply]

Replies are listed 'Best First'.

Re^5: Use of uninitialized value $1
by Marshall (Canon) on Aug 26, 2016 at 03:15 UTC

perlre

NOTE: Failed matches in Perl do not reset the match variables, which makes it easier to write code that tests for a series of more specific cases and remembers the best match.

Update: After some reflection, my memory recalls some situation where there were several capture groups, $1,$2,$3. Overall, the match failed, but the first part ($1) did match and change $1 although the rest of the expression $2,$3 didn't match and didn't change. This behavior was version specific. So, this is a cautionary note that despite what the doc says, there may be some "bite you" case out there that my super-search foo is not able to find.

[reply]