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Perl command modification

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Top Forums Shell Programming and Scripting Perl command modification
# 1  
Old 10-25-2014
Perl command modification
below is a snippet of code from a larger perl code:


Code:
my $uname = ( -e '/usr/bin/uname' ) ? '/usr/bin/uname' : '/bin/uname';
my $os = ( `$uname 2>/dev/null` );

when i run this code, it seems to be complaining about the backticks. is there any efficient way i can get rid of the backticks and still be able to run the command and assign its value to the variable $os???

i tried this:

Code:
my $uname = ( -e '/usr/bin/uname' ) ? '/usr/bin/uname' : '/bin/uname';
my $os = ( $( $uname 2>/dev/null)  );

but it didn't work.


OS:
Linux RedHat
# 2  
Old 10-25-2014
Try like this

Code:
akshay@nio:/tmp$ cat p.pl
#!/usr/bin/perl

use warnings;
use strict;

foreach my $cmd (('/bin/uname -a','ls -ltr','pwd')){

open CMD,'-|',"$cmd" or die $@;
my $line;
print "\nCommand : $cmd \n";
while (defined($line=<CMD>)) {
    print $line; 
}
close CMD;

}

Code:
akshay@nio:/tmp$ perl p.pl

Command : /bin/uname -a 
Linux Aix 3.8.0-29-generic #42~precise1-Ubuntu SMP Wed Aug 14 15:31:16 UTC 2013 i686 i686 i386 GNU/Linux

Command : ls -ltr 
total 72
drwx------ 2 akshay akshay 4096 Jan  1  1970 orbit-akshay
drwx------ 2 root   root   4096 Oct 25 20:38 pulse-PKdhtXMmr18n
drwx------ 2 root   root   4096 Oct 25 20:38 pulse-2L9K88eMlGn7
-rw-rw-r-- 1 akshay akshay    0 Oct 25 20:39 unity_support_test.0
drwx------ 2 akshay akshay 4096 Oct 25 20:39 ssh-SRRdshaL1886
drwx------ 2 akshay akshay 4096 Oct 25 20:39 keyring-cfR6TC
drwx------ 2 akshay akshay 4096 Oct 25 20:39 pulse-ZUhHRVImGZzf
-rw------- 1 akshay akshay    0 Oct 25 20:40 tmpx9PyKR
-rw-r----- 1 akshay akshay   32 Oct 25 20:51 adb.log
drwxr--r-- 2 akshay akshay 4096 Oct 25 20:51 android-akshay
-rw-rw-r-- 1 akshay akshay 1838 Oct 25 20:51 filef8zK8X
drwxrwxrwx 2 akshay akshay 4096 Oct 25 20:52 swtlib-32
drwxr-xr-x 2 akshay akshay 4096 Oct 25 20:52 hsperfdata_akshay
-rw-rw-r-- 1 akshay akshay  314 Oct 25 21:16 cmp.awk~
-rw-rw-r-- 1 akshay akshay  314 Oct 25 21:16 cmp.awk
-rw-rw-r-- 1 akshay akshay 1125 Oct 25 21:16 p~
-rw-rw-r-- 1 akshay akshay 1156 Oct 25 21:16 p
-rw-rw-r-- 1 akshay akshay  127 Oct 25 21:28 f
-rw-rw-r-- 1 akshay akshay  232 Oct 25 22:21 p.pl~
-rw-rw-r-- 1 akshay akshay  234 Oct 25 22:21 p.pl

Command : pwd 
/tmp

---------- Post updated at 11:39 PM ---------- Previous update was at 11:24 PM ----------

OR you can create small subroutine like this

Code:
#!/usr/bin/perl

use warnings;
use strict;


sub system_cmd{
	my @return;
	open CMD,'-|',"@_" or die $@;
	my $line;
	while (defined($line=<CMD>))
	{
	    	push(@return, $line); 
	}
	close CMD;
	return @return;
}


foreach my $cmd (('/bin/uname -a','ls -ltr','pwd'))
{
	my @output =system_cmd($cmd);
	
	print "\nCommand : $cmd \n";
	print "@output";
}

This User Gave Thanks to Akshay Hegde For This Post:
SkySmart
# 3  
Old 10-25-2014
Use system. Here's an example.
Code:
[user@host ~]$ perl -e 'system("date")'
Sun, Oct 26, 2014  7:38:44 AM
[user@host ~]$

This User Gave Thanks to balajesuri For This Post:
SkySmart
# 4  
Old 10-25-2014
Quote:
Originally Posted by SkySmart
Code:
my $uname = ( -e '/usr/bin/uname' ) ? '/usr/bin/uname' : '/bin/uname';
my $os = ( `$uname 2>/dev/null` );

when i run this code, it seems to be complaining about the backticks. is there any efficient way i can get rid of the backticks and still be able to run the command and assign its value to the variable $os???
It would be interesting to know what kind of backticks complains you get. The posted snippet should work exactly what you want.
You could remove the 2>/dev/null out of it since the backtick captures only the STDOUT by default and ignores the SDTERR

Also, you can remove the backticks if you use qx.
e.i
Code:
my $os = qx{$uname};

The most common ways of executing external commands:
There are some examples in that site and some more explanations.

A synopsis found in that link:
  1. system(): you want to execute a command and don't want to capture its output
  2. exec: you don't want to return to the calling perl script
  3. backticks: you want to capture the output of the command
  4. open: you want to pipe the command (as input or output) to your script
This User Gave Thanks to Aia For This Post:
SkySmart
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