Using Perl instead of awk!

[Ragged Robin]

Hey guys, I just need an example of how to express something in Perl the way I know how to do it with awk.

Ideally I would like to do something like this:

my $pSWP = `awk '/something/ { print $3 }' /dir/file`;

But the value of $pSWP appears to be null when I can confirm that the awk command should return a value when ran on the system. Apparently doing something like this is kind of a no-no and I can do the same thing in Perl but I'm not sure what all is available to do this in only Perl :(

[eyepopslikeamosquito]

Something like this should get you started:

use strict;
use warnings;
my $fname = '/dir/file';
open my $fh, '<', $fname or die "error: open '$fname': $!";
while (<$fh>) {
    next unless /something/;
    my @flds = split;
    print "$flds[2]\n";
}

See open and split.

[choroba]

Backquotes interpolate variables, and $3 is a special variable in Perl. So, Perl interpolates it (but it's probably empty, do you use warnings?) before awk can see it. You can prevent interpolation by backslashing the dollar sign. But... Why would you call awk from Perl? You can get the same result without shelling out.

[runrig]

The result is more verbose than it needs to be, but the last part is fairly straightforward:

 $ a2p <<'EOT'
> /something/ { print $3 }
> EOT
#!/usr/local/bin/perl
eval 'exec /appl/toolbox/perl5.8.8/bin/perl -S $0 ${1+"$@"}'
    if $running_under_some_shell;
                        # this emulates #! processing on NIH machines.
                        # (remove #! line above if indigestible)

eval '$'.$1.'$2;' while $ARGV[0] =~ /^([A-Za-z_0-9]+=)(.*)/ && shift;
                        # process any FOO=bar switches

$, = ' ';               # set output field separator
$\ = "\n";              # set output record separator

while (<>) {
    ($Fld1,$Fld2,$Fld3) = split(' ', $_, -1);
    if (/something/) {
        print $Fld3;
    }
}

Updated/fixed...single quoted 'EOT'

[Tux]

When you do know awk, and want to see/learn how the same thing is done in perl, you can use the awk-to-perl tool a2p that shipped with perl. The generated perl code is probably (very) inefficient, but at least shows you how the conversion could be done:

$ echo '/something/ { print $3 }' | a2p
#!/pro/bin/perl
eval 'exec /pro/bin/perl -S $0 ${1+"$@"}'
    if $running_under_some_shell;
                        # this emulates #! processing on NIH machines.
                        # (remove #! line above if indigestible)

eval '$'.$1.'$2;' while $ARGV[0] =~ /^([A-Za-z_0-9]+=)(.*)/ && shift;
                        # process any FOO=bar switches

$, = ' ';               # set output field separator
$\ = "\n";              # set output record separator

while (<>) {
    ($Fld1,$Fld2,$Fld3) = split(' ', $_, -1);
    if (/something/) {
        print $Fld3;
    }
}

[karlgoethebier]

Not sure if i got it... but turn on auto split

karls-mac-mini:monks karl$ echo foo bar nose cuke  > file
karls-mac-mini:monks karl$ echo foo bar nose cuke  >> file

karls-mac-mini:monks karl$ cat file
foo bar nose cuke
foo bar nose cuke

# bullshit! perl -lnae 'print $F[3];' file
perl -lne '/(cuke)/;print $1' file
cuke
cuke
karls-mac-mini:monks karl$

Update: Shit! Did you mean this?

See perlrun.

Regards, Karl

[codiac]

For your code to work you need to escape the '$' awk is using:

my $pSWP = `awk '/something/ { print \$3 }' /dir/file`;

But like others said, why use awk when you can do it in perl :)