You need to insert semicolons between all your statements, including at the place that the syntax error occurs.

Please see perlintro and perlsyntax for detail.

open FILE,"config.txt" or die "cannot open file : $!";
while(<FILE>) { 
$ip = ($_ =~ m/(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})/ ) 
print "$ip"; 
# print $_; 
}
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After line 3, of course. Have you tried running the code? Also, prepending some spaces to the lines in the loop would not harm anybody.
لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

No I haven't tried to run the code choroba. I've just tried to point ulaksh to the right direction when it comes to syntax :-) .

Please, format your post question effectively
Even when that is done. There are other some other best practice I think you should still look into.

• Avoid barewords usage like FILE, FH, etc. Instead use a lexically scoped variable like $fh etc
• use use warnings; use strict;
• use the 3 argument open function like so:open my $fh, '<',"config.txt" or die "cannot open file : $!";
• Close your file handles like so: close $fh or die "can't close file: $!";
• Your construction here will only print "1", after you have corrected the syntax error
  Use this instead:
  

  ...
  while(<$fh>){
  
    chomp;
      (my $ip =
         $_) =~ m/(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})/; 
    print $ip,$/;
  }
  ...
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  I think is even alot better to TEST each of your matched value using "if" like so:

  ...
  while (<$fh>) {
    chomp;
      my $ip="";
      if (m/(?<matched_ip>(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}))/){
        $ip = $+{matched_ip};
      } 
    print $ip,$/;
  }
  ...
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Please note that
    my $m = ($s =~ m/(\d{1,3})/);
returns the success (true or false) of the match, and
    my ($d) = $s =~ m/(\d{1,3})/;
returns the captured substring, if any. (And the enclosing parentheses are irrelevant in the  ($s =~ m/(\d{1,3})/) expression in this case.) See perlre, perlretut and perlrequick.

>perl -wMstrict -le
"my $s = 'a987b';
 my $m = ($s =~ m/(\d{1,3})/);
 print qq{'$m'};
 my ($d) = $s =~ m/(\d{1,3})/;
 print qq{'$d'};
"
'1'
'987'
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Also, it might be better to use the  $RE{net}{IPv4} regex from Regexp::Common::net (see Regexp::Common as the general interface module) to match the IP.