Consider the following snippet:

use strict;
use warnings;
my $str = "Title: Learning Perl  Author: Schwartz, Randal L.  ISBN: xx
+xx";
if ( $str =~ /^Title: (.*)\s+Author: (.*)\s+ISBN: (.*)/ ) {
  # print "<$1><$2><$3>\n";
  my $author = $2;
  $author =~ s/\.//g; # Remove full stops (periods)
  print "<$1><$author><$3>"; # Line 8
}

[download]

The output I get is:

Use of uninitialized value <snip> line 8.
Use of uninitialized value <snip> line 8.
<><Schwartz, Randal L ><>

[download]

What has happened to $1 and $3?

According to perldoc perlre:

The scope of $<digit> extends to the end of the enclosing BLOCK or eval string, or to the next successful pattern match, whichever comes first.

which I understand to mean that $1 and $3 should still be in scope.

Interestingly, if the substitution fails (ie here if there is no "." in $author to substitute), line 8 works as expected...

Version: AS Perl 5.61 Win ME and XXXX

Please note: I'm not looking for alternative or "better" ways of parsing such a string; I can think of several. My question is only why this way doesn't work.

TIA

dave

In reply to Modifying value of $1 clobbers $2, $3 etc? by Not_a_Number

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