A few points about your code.

• In your pattern \d{1} is exactly the same as saying \d, IOW a quantifier of one is implicit and needn't be stated.

• Be aware that a full stop is a regular expression metacharacter matching any character (with caveats, see perlre) so did you mean to match a decimal point in this pattern /returns \d{1} \(in \d{1}.\d{6} secs/? Consider this code

  $ perl -le '
  > print
  >    m{\d{1}.\d{6}}
  >    ? qq{$_: Matched}
  >    : qq{$_: No match}
  >    for
  >       q{in 1.234567 secs},
  >       q{in 12345678 secs},
  >       q{in 3A987654 secs};'
  in 1.234567 secs: Matched
  in 12345678 secs: Matched
  in 3A987654 secs: Matched
  $
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  You will need to escape the dot if you want a decimal point

  $ perl -le '
  > print
  >    m{\d{1}\.\d{6}}
  >    ? qq{$_: Matched}
  >    : qq{$_: No match}
  >    for
  >       q{in 1.234567 secs},
  >       q{in 12345678 secs},
  >       q{in 3A987654 secs};'
  in 1.234567 secs: Matched
  in 12345678 secs: No match
  in 3A987654 secs: No match
  $
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  Now only a literal full-stop is matched.

• Consider using the three-argument form of open with lexical filehandles.

• Avoid using the variable names $a and $b as they are special and should be reserved for use in sort routines.

I hope these points are helpful.

#!/usr/bin/perl

use strict;

my $string = 'to test me';
$string =~ /to\s(\w+)\s/;

print $1;
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Thanks. I didnt know, $1 is carried over. Dumb me though I thought about it. Thanks

Check perlre's "Capture buffers". Also Use strict warnings and diagnostics or die!

use strict;
use warnings;

my $a = 'a.txt';
open(my $in ,'<', $a) || die "cannot open $a for reading: $!";
my $b = 'time.txt';
open (my $out,">>$b") || die "cannot create $b: $!";
while (<$in>) {
    # read a line from file $a into $_ 
    #print $out $_;
    if (/(returns \d{1} \(in \d{1}.\d{6} secs)/) {
        ## use capturing
        print $out $1."\n" ;
    }
    
} 
close($in)    || die "can't close  $a:$!"; 
close($out) || die "can't close  $b:$!";
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