In Perl, how can I print lines read from a file with optional leading whitespace removed?

Question

#!/usr/bin/perl 
open(SARAN,"first.txt") or die "Can't Open: $!\n";
while($line=<SARAN>)
{ 
print "$line\n";
} 
close SARAN;

Hi, In the above perl script, i need one functionality... in first.txt, each line starts with some space in front.. I need to print the lines without space in front... What to do.

thanks..

Answer 1

you can do:

while($line=<SARAN>) { 
  $line=~s/^\s+//;  # delete the leading whitespace.
  print "$line\n";
}

We use the Perl's substitute operator s which allows us to find a match using a regex and replace the part of the string that matched with another string.

Here we use the regex ^\s+

• ^ is the start anchor.
• \s is any whitespace character.
• + quantifier to mark one or more

Basically we match and replace the leading one or more whitespace char with nothing which effectively means deleting them.

Answer 2

Your question is ambiguous: Do you want to print the lines that do not start with space(s) or print all the lines after removing any leading space(s)?

@codaddict showed how to do the latter. I will show how to do the former:

#!/usr/bin/perl 

use strict;
use warnings;

open my $SARAN, '<', "first.txt" 
    or die "Can't open 'first.txt': $!";

while (my $line = <$SARAN>) 
{ 
    print $line unless $line =~ /^\s/;
} 

close $SARAN;

Note the following:

• use strict will help you catch programming errors.
• use warnings will alert you to dubious constructs.
• Bareword filehandles such as SARAN are package globals. Use lexical filehandles.
• Prefer the three-argument form of open, especially if the filename is not hardcoded.
• Include the filename in the error message.
• Since you are not chomping $line, print "$line\n" would cause newlines to be doubled.