Perl find-and-replace (with numbered replacement) enters infinite loop - regex

Question

Earlier today I posted a similar question, whose solution leads to a new problem, -,-
Well, the story is that I want Perl to capture comments from a text, store them in array, and replace them with new numbered comments, say, for original $txt:
//first comment
this is a statement //second comment
//third comment
more statements //fourth comment
I wanna push the 4 comments into an array, and get new $txt like:
//foo_0
this is a statement //foo_1
//foo_2
more statements //foo_3
I tried the following Perl:
$i=0;
$j=0;
#while ($txt =~ s/(\/\/.*?\n)/\/\/foo_$i\n/gs) {
#while ($txt =~ s/(\/\/.*?\n)/\/\/foo_$i\n/s) {
#foreach ($txt =~ s/(\/\/.*?\n)/\/\/foo_$i\n/gs) {
foreach ($txt =~ s/(\/\/.*?\n)/\/\/foo_$i\n/s) {
if(defined $1) {
push (#comments, $1);
print " \$i=$i\n";
$i++
}
print " \$j=$j\n";
$j++;
}
print "after search & replace, we have \$txt:\n";
print $txt;
foreach (0..$#comments) {
print "\#comments[$_]= #comments[$_]";
}
In it, I tried the "while/foreach (... s///gs)" in four flavors, but none of them actually did what I want.
The "foreach" statement will work on the text only once; and more worse, the "while" statement will enter endless loop, seems like the new "//foo_xx" stuff is put back into the string for further search operations, making it an infinite iteration. It's so strange that such a seemingly simple search-and-replace mechanism would get mired in endless loop, or there're some obvious tricks that I don't know of?
BTW, I already went through the post by highsciguy . For him, "simply replacing while with foreach in the above code will do"; but for me the foreach just does not work, I don't know why.
Anyone get any ideas in helping me with this? Thanks~

Answer 1

I'd tackle it a bit differently - a while loop to read a filehandle line by line, and 'grab' all the comment lines out of it.
Something like this:
#!/usr/bin/perl
use warnings;
use strict;
my #comments;
#iterate stdin or filename specified on command line
while ( <> ) {
#replace anything starting with // with foo_nn
#where nn is current number of comments.
s,//(.*),"//foo_".#comments,e && push (#comments, $1 );
#$1 is the contents of that bracket - the string we replaced
#stuff it into commments;
#print the current line (altered by the above)
print;
}
#print the comments.
print "Comments:\n", join "\n", #comments;
Doesn't address duplicates, and will break if you've got // in quotes or something, but does work for your example. while iterates based on a filehandle, line by line. If you've got a scalar with your text blob already, then you can accomplish the same thing with foreach ( split ( "\n", $text ) ) {
Output:
//foo_0
this is a statement //foo_1
//foo_2
more statements //foo_3
Comments:
first comment
second comment
third comment
fourth comment

Answer 2

Iterate over every line of the text, and if replacement is successful, store the comment:
#!/usr/bin/perl
use strict;
use warnings;
my $txt = <<END; # define text
//first comment
this is a statement //second comment
//third comment
more statements //fourth comment
END
my #comments = ();
my $i = 0;
foreach (split qq(\n), $txt) { # iterate over input lines
if (s&(//.*)&//foo_$i&) { # do we match?
push #comments, $1; # then push comment
$i++; # and increase counter
}
print; # print modified row
print qq(\n); # print newline
}
print qq(\nComments:\n);
foreach (#comments) {
print; # print the comment
print qq(\n); # print newline
}