perl array for non-zero values

Question

Im trying to code a "service" script based on "ps". my code:

#!/usr/bin/perl
use strict;
use warnings;
die "usage:    $0 <service name>\n" unless $ARGV[0];
my $service = $ARGV[0];
open(my $ps, "ps -aux |") || die "Uknown command\n";
my @A = <$ps>;
close $ps;
foreach my $i(grep /$service/, @A){
    chomp $i;
    if($i=~ /root/){
        next
    }
    print "$i\n";
}

My problem: When running the script against undef arg like:

$0 blablabla

I want to return an output if there is no such service appears/when returns 0 Thanks

TLP · Accepted Answer · 2013-03-04 17:25:19Z

2

I assume what you are asking is: How to give a proper message when no matching lines are found?

Well, just store the result in an array instead:

my @lines = grep { !/root/ && /$service/ } @A;

if (@lines) {   # if any lines are found
    for my $line (@lines) {
        ...
    }
} else {
    print "No match for '$service'!\n";
}

Or you can print the number of matches regardless of their number:

my $found = @lines;
print "Matched found: $found\n";

Note also that you can add the check for root in your grep.

As a side note, this part:

die "usage:    $0 <service name>\n" unless $ARGV[0];
my $service = $ARGV[0];

Is perhaps better written

my $service = shift;
die "usage ...." unless defined $service;

Which specifically checks if the argument is defined or not, as opposed to true or not.

edited Mar 4, 2013 at 17:25

answered Mar 4, 2013 at 17:19

TLP

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Comments

choroba · Accepted Answer · 2013-03-04 17:16:49Z

2

If I understand you correctly, you want to inform the user if no such service was found? If so, you can modify the script as follows:

my $printed;                        # Will be used as a flag.
foreach my $i(grep /$service/, @A){
    chomp $i;
    if($i=~ /root/){
        next
    }
    $printed = print "$i\n";        # Set the flag if the service was found.
}
warn "No service found\n" unless $printed;

answered Mar 4, 2013 at 17:16

choroba

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Comments

gpojd · Accepted Answer · 2013-03-04 17:17:57Z

1

You can try something like this:

my @processes = grep /$service/, @A;
if ( scalar @processes ) {
    foreach my $i( @processes ){
        chomp $i;
        if($i=~ /root/){
            next;
        }
        print "$i\n";
    }
}
else {
    print 'your message';
}

answered Mar 4, 2013 at 17:17

gpojd

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Comments

Birei · Accepted Answer · 2013-03-04 17:18:16Z

0

You could check the result of the grep command before traversing it in the for loop, like:

...

my @services = grep { m/$service/ } @A;

# Filter the perl process running this script and...
if ( ! @services ) { 
    print "No service found\n";
    exit 0;
}

foreach my $i( @services ){
    ...
}

Take into account that the grep command will never give a false return because it is including the perl process, so you will have to filter it, but I hope you get the idea.

answered Mar 4, 2013 at 17:18

Birei

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1 Comment

Raid5 Over a year ago

I got it. This is actually the logical way, however my code [not posted here] didn't work. Thanks

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