Neither of those produces the desired output for me. $x is never incremented. Since you require a space at the end of the string-to-be-substituted, there is no substitution after the last abc, and the desired spacing in the output is wrong:

abc def(1)abc abc abc
abc def(1)abc def(1)abc abc
abc def(1)abc def(1)abc def(1)abc

Done. string = 'abc def(1)abc def(1)abc def(1)abc'
[download]

Putting $x++; in your while loop after the substitution will fix the former, but not the latter.

Following on the other examples in this thread, one possibility is the following:

1:

my $string = "abc abc abc abc";
my $x = 1;
# while ( $string =~ /abc /ig ) {
while ( $string =~ /abc/ig ) {
    my $i = pos($string);
#    substr( $string, $-[0], $+[0]-$-[0]) =~ s/(abc) /$1 def($x)/;
    substr( $string, $-[0], $+[0]-$-[0]) =~ s/(abc)/"$1 def(" . $x++ .
+")"/e;
    print "$string\n";
    pos($string) = $i + 6;
}
[download]

2:

my $string = "abc abc abc abc";
my $x = 1;
# while ( $string =~ /(?=abc )/ig ) {
while ( $string =~ /(?=abc)/ig ) {
    my $i = pos($string);
#    $string =~ s/\G(abc) /$1 def($x)/;
    $string =~ s/\G(abc)/"$1 def(" . $x++ . ")"/e;
    print "$string\n";
    pos($string) = $i + 6;
}

print "\nDone. string = '$string'\n";
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.