Where does the double backslash in \\K come from? Here is a complete working example:

#!/usr/bin/perl 

use strict;
use warnings;

sub processReplacements {
    my $regexM = shift @_;    #TERM(S) TO MATCH
    my $regexR = shift @_;    #REPLACEMENT TERM
    my $regexI = shift @_;    #FLAG FOR CASE-INSENSITVE SUBSTITUTION
    my $sv       = shift @_;  # $sv => START, E.G. /^(.*)/; 
    my $ev       = shift @_;  # $ev => END, E.G. /(.*)$/; 
    my $ww       = shift @_;  # $ww => WHOLE-WORD, E.G. /\b(.*)\b/; 
    my $ch       = shift @_;  # $ch => DELIMIT CHARS, 
                # E.G. /[.,:;!?'"](.*)[.,:;!?'"]/;
    my @data = @_;        # INCOMING ARRAY
    my @changed = ();    # OUTGOING ARRAY
    my $line = '';        
    my $linehead = '';
    my $sourceline = '';

    my $m = $regexI ? qr{(?i:$regexM)} : qr($regexM);
    my $s = $sv ? qr(^) : qr();
    my $e = $ev ? qr($) : qr();
    my $b = $ww ? qr(\b) : qr();
    my $c = $ch ? qr([.,:;!?'"]) : qr();

    foreach my $line (@data) {
        push @changed, $line =~ s{$s$c$b\K$m(?=$b$c$e)}{$regexR}r;
    }
    return @changed;
}

foreach my $parm (qw(0:0:0:0:0 1:0:0:0:0 0:1:0:0:0 0:0:1:0:0 0:0:0:1:0
+ 0:0:0:0:1)) {
    my @opts = split /:/, $parm;
    print "parm: $parm\n";
    my @r = processReplacements('xxx', 'yyy', @opts,
    'aaaxxxbbb', 'aaa xxx bbb', 'aaa:xxx:bbb', 'xxxbbb', 'aaa:XXX', 'a
+aaxxx');
    print "$_\n" foreach @r;
    print "\n";
}
[download]

which gives:

parm: 0:0:0:0:0
aaayyybbb
aaa yyy bbb
aaa:yyy:bbb
yyybbb
aaa:XXX
aaayyy

parm: 1:0:0:0:0
aaayyybbb
aaa yyy bbb
aaa:yyy:bbb
yyybbb
aaa:yyy
aaayyy

parm: 0:1:0:0:0
aaaxxxbbb
aaa xxx bbb
aaa:xxx:bbb
yyybbb
aaa:XXX
aaaxxx

parm: 0:0:1:0:0
aaaxxxbbb
aaa xxx bbb
aaa:xxx:bbb
xxxbbb
aaa:XXX
aaayyy

parm: 0:0:0:1:0
aaaxxxbbb
aaa yyy bbb
aaa:yyy:bbb
xxxbbb
aaa:XXX
aaaxxx

parm: 0:0:0:0:1
aaaxxxbbb
aaa xxx bbb
aaa:yyy:bbb
xxxbbb
aaa:XXX
aaaxxx
[download]

-jo

That's a great question, and until you asked it, I hadn't even caught that. (I had just copy/pasted the error straight from the log, and noticed it was focused on that regex section.)

The code did not contain a double backslash. I copied that line exactly as you had posted it, and it was and still is as follows in the code:

foreach my $line (@data) {
    push @changed, $line =~ s{$s$c$b\K$m(?=$b$c$e)}{$regexR}r;
}
[download]

I haven't used the //r before. That is new to me. What does it do? I wondered if it might be the syntax error.

Blessings,

~Polyglot~

It means:

Return substitution and leave the original string untouched.

Maybe it is not available in your version. But you may work around this.

-jo

The  /r modifier for  s/// substitution was added with Perl version 5.14 (see Regexp Quote-Like Operators in perlop). What version of Perl are you using?

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