perl filter output from system command

Question

I try to get a specific output from a simple perl command en write it to a variable to use in a later stadium in my script.

I have to following code:

#!/usr/bin/perl

use strict;
use warnings;


my $serial = system("hdparm -I /dev/sda | grep 'Serial Number:'");
print $serial;

This generates the following output:

0root@spool-B-01:~# ./test.pl
    Serial Number:      9VS3D79X

But i need the output to be as followed:

0root@spool-B-01:~# ./test.pl
9VS3D79X

I have tried some things with awk and sed. But that won't give the output the way i need it.

For example:

#!/usr/bin/perl

use strict;
use warnings;
use Sys::Hostname;


my $serial = system("hdparm -I /dev/sda | grep 'Serial Number:' | sed -e 's/Serial Number://g'");
print $serial;

Show the output like:

0root@spool-B-01:~# ./test.pl
          9VS3D79X

It is almost correct but you still got the tabs before the serial code.

I hope that somebody can help me figure this stuff out and do it the correct way.

If you're coding in Perl, why use `grep`, `awk`, `sed`, etc? — Biffen, Apr 08 '14 at 10:00

score 3 · Accepted Answer · edited May 23 '17 at 11:49

There are various ways to launch system commands from perl: system, exec, and backtic are the most popular choices. Some capture output, some don't. For a good rundown check this link: What's the difference between Perl's backticks, system, and exec?

In this case, however, backtick is most appropriate:

For example a quick script such as:

my $out = `ls`;
print "$out \n";

Will print out the results of ls to the screen.

In your case I would try:

my $command = "hdparm -I /dev/sda | grep 'Serial Number:' | sed -e 's/Serial Number://g'";

my $serial = `$command`;
print $serial;  #white space 

#Remove whitespace
$serial =~ s/^(\s+)//g;  

print $serial;  #No white space

I have a mac in front of me so I don't have access to the hdparm command

With regards to the whitespace removal \s is the white space character so the regex

s/^\s+//g;

translates to replace all white space starting from the start of the line with nothing

Yeah this works. But i still got the tabs before the serial number. Any idea how to fix that? — Mitchel, Apr 08 '14 at 12:56

score 2 · Answer 2 · edited Apr 08 '14 at 11:43

2

#!/usr/bin/perl

use strict;
use warnings;
use autodie;

open my $fh, '-|', 'hdparm -I /dev/sda';
while (<$fh>) {
    print "$_\n" if s/Serial Number://g;
}
close $fh

edited Apr 08 '14 at 11:43

mpapec

50,217
8
67
127

answered Apr 08 '14 at 11:18

glenn jackman

238,783
38
220
352

Filippo Lauria · Answer 3 · 2014-04-08T12:01:01.983

-1

Try this:

#!/usr/bin/perl
use strict;
use warnings;

my @serial = `hdparm -I /dev/sda`;
foreach my $line (@serial) {
  print $1 if ($line =~ /(?:\s+)Serial Number:(?:\s+)(\w+)/);
}

Output:

root@spool-B-01:~# ./test.pl
9VS3D79X

edited Apr 08 '14 at 12:01

answered Apr 08 '14 at 10:06

Filippo Lauria

1,965
14
20

perl filter output from system command

3 Answers3

Try this:

Output: