Re: Replacing a specfied instance of a pattern in a string

my $str      = 'Fsih my test variable is fsihd or is it gfsih or gfsih
+d fsih';
#                                        1111            2222     3333
+  4444
my $substr   = 'fsih';
my $replace  = 'fish';
my $instance = 3;  # 3rd

print("$str\n");

my $pos = -length($substr);

for (;;) {
   last if !$instance--;
   $pos = index($str, $substr, $pos + length($substr));
   last if $pos < 0;
}

substr($str, $pos, length($substr), $replace)
   if $pos >= 0;

print("$str\n");
[download]

Update: Fixed off-by-one error.

Comment on Re: Replacing a specfied instance of a pattern in a string Download Code

Replies are listed 'Best First'.
Re^2: Replacing a specfied instance of a pattern in a string by Roy Johnson (Monsignor) on Jul 14, 2005 at 22:01 UTC
A tad simpler looping, and case-insensitive: `my $foo = 'Fsih my test variable is fsihd or is it gfsih or gfsihd f +sih'; my $from = 'fsih'; my $which = 3; my $to = 'FISH'; # makes it easy to see $foo =~ /\Q$from\E/ig for (1..$which); substr($foo, pos($foo) - length($from), length($from), $to) if pos($fo +o); print "Foo = $foo\n";` [download] Caution: Contents may have been coded under pressure.	[reply] [d/l]
Re^3: Replacing a specfied instance of a pattern in a string by ikegami (Patriarch) on Jul 14, 2005 at 22:48 UTC
That reminds me of `/c`! `my $str = 'Fsih my test variable is fsihd or is it gfsih or gfsih +d fsih'; # 1111 2222 3333 + 4444 my $substr = 'fsih'; my $regexp = qr/\Q$substr\E/; my $replace = 'fish'; my $instance = 3; # 3rd print("$str\n"); scalar $str =~ /\G.?$regexp/gc while --$instance; $str =~ s/\G(.?)$regexp/$1$replace/; print("$str\n");` [download] The `/c` is needed in case there are less than $instance instances of the search string.	[reply] [d/l] [select]
Re^2: Replacing a specfied instance of a pattern in a string by krisahoch (Deacon) on Jul 14, 2005 at 21:35 UTC
Now, is there a way to do it with Regular Expression?	[reply]
Re^3: Replacing a specfied instance of a pattern in a string by ikegami (Patriarch) on Jul 14, 2005 at 21:36 UTC
`my $str = 'Fsih my test variable is fsihd or is it gfsih or gfsih +d fsih'; # 1111 2222 3333 + 4444 my $substr = 'fsih'; my $regexp = qr/\Q$substr\E/; my $replace = 'fish'; my $instance = 3; # 3rd print("$str\n"); my $pre_count = $instance - 1; $str =~ s/((?:$regexp.*?){$pre_count})$regexp/$1$replace/; print("$str\n");` [download] You might have noticed both of these are case sensitive. Both can be made case-insensitive. The non-regexp version is most likely much faster. The regexp version can handle regexps instead of constant strings.	[reply] [d/l]


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