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PERL: removing blank lines from multiple files


 
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# 8  
Old 09-19-2009
Quote:
Originally Posted by ilikecows
Look at my above post. It does just that.
Thanks, but i really cant believe a perl one liner exists to do this, but the only way to do this omside an actual perl script is to run system() to run sed, then run system() again to run cp to copy the file back over


surely ?
# 9  
Old 09-19-2009
You can write something like this (untested).
Backup your files first!


Code:
#! /usr/bin/env perl

use warnings;
use strict;

my @files   = glob '/tmp/*'; # adjust the glob!
my $logfile = $0 . '.log';

open LH, '>', $logfile or die "open $logfile: $!\n";

for (@files) {
    {
        local ( $^I, @ARGV ) = ( '', $_ );
        while (<>) {
            print LH $ARGV, ": record ", $., "\n" and next if /^\s*$/;
            print;
        }
    }
}

close LH or warn "close $logfile: $!\n";


Last edited by radoulov; 09-19-2009 at 04:18 PM..
# 10  
Old 09-19-2009
Quote:
Originally Posted by hcclnoodles
...
..the reason i have to go through each file line by line is because i need to identify exactly which line number in which file is returning blank ...
...
That's not a good enough reason.
You do not have to
(1) open
(2) read and
(3) close a file

just to find out which line number is blank. Sure, you can, but you don't have to.
If you do, then it's a convoluted way of doing things. The sed program didn't open, read, and close the file (at least explicitly).

Quote:
...
to identify exactly which line number in which file is returning blank and send it to a log file.
...
Send the blank line to a log file ? This wasn't the requirement in your original post.

Quote:
...
there is no need for me to actually fix these issues within this actual script but i thought it make sense to do so if possible
...
Not sure I understand this. If there is no need to fix it, then why do you even want to do it ?
As for the possibility, you opened the file for reading (the default). And you wanted to write to a file. They are not the same thing.

Quote:
...
I read on another site that I can set my file location within my script to say $file and then run this
Code:
my $file = "/var/tmp/0629AN1208.net";
$file =~ s/^\n//g;

but that doesnt seem to work,
...
Of course it doesn't, if you understand what you are trying to do. "$file" is just a variable, not an actual file. And the "s///" operator simply works on the value of that variable. Your variable did not have a newline character at the beginning, so it wasn't removed. If it had, then it would've been removed -

Code:
$ 
$ perl -le '$file = "
/var/tmp/0629AN1208.net"; print "Before: $file"; $file =~ s/^\n//g; print "After : $file"'
Before: 
/var/tmp/0629AN1208.net
After : /var/tmp/0629AN1208.net
$ 
$

Perl is simply doing what it was told to do.
And if you are thinking that the "s///" operator will actually open a file and remove newlines, just because the variable was called "$file", then you need to brush up on the basics first.

Quote:
...
whereas if i run the equivalent one liner from the command line (see below) it works perfectly .

Code:
perl -pi -e "s/^\n//" /var/tmp/0629AN1208.net

...
That one-liner writes to the file because of that qualifier "-i". Check the perl documentation. You could make it work on a hierarchy of files, but the solution would be more verbose than that sed solution.

tyler_durden
# 11  
Old 09-20-2009
Here is what you can do:

1. A seperate script using sed to remove the blank lines
2. Call sed from within your perl script with system
3. The perl -i route in the above post
4. Dump each line of the file to an array except blank lines, open the files again for writing, and clobber them with the contents of the array
5. Create a new file, open it for writing, add an else to the if ( /^$/ ) that counts blank lines, and print the non blanks to the new file. Then overwrite the original with the new one.

1,2, and 3 are much easier than 4 or 5.
# 12  
Old 09-20-2009
thank you for your responses, I have been learning perl for the grand total of 5 weeks now...so go easy on me Smilie

i will look at using the sed solution instead

thanks again

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