in reply to How do I use grep in a script

Converting the steps from a shell pipeline to Perl is fairly easy. The steps are:

  1. grep Acct: Facs_Data.txt - Read a file line by line and select the lines matching Acct:
  2. cut -d":" -f2 - Take the side to the right of : of the line
  3. cut -d" " -f1 - take the side to the left of the blank of the line

If we convert each step to Perl, we get the following parts:

  1. my $filename = 'Facs_Data.txt';
open my $fh, '<', $filename
    or die "Couldn't open '$filename': $!";

my @lines = grep { /Acct:/ } <$fh>; # Read a file line by line and sel
+ect the lines matching Acct:

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  2. @lines = map { [ split $_, /:/ ]->[1] } @lines; # Take the side to the
+ right of : of the line

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  3. @lines = map { [ split $_, /:/ ]->[0] } @lines; # take the side to the
+ left of the blank of the line

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But a more perlish approach would be to do all that in one go:

my $filename = 'Facs_Data.txt';
open my $fh, '<', $filename
    or die "Couldn't open '$filename': $!";

my @lines = map  { /:([^\s]+)/ ? $1 : () } # take the stuff between th
+e : and the first blank
            grep { /Acct:/ } <$fh>; # Read a file line by line and sel
+ect the lines matching Acct:

# do whatever with the values in @lines
print "$_\n" for @lines;

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Update:: Fixed missing = in step three, spotted by AnomalousMonk, thanks.

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Re^2: How do I use grep in a script
by ikegami (Patriarch) on Dec 26, 2017 at 17:35 UTC 
    map  { /:([^\s]+)/ ? $1 : () } grep { /Acct:/ }

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    is a long way to write 
    map  { /Acct:([^\s]+)/ }

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[reply]
[d/l]
[select]
      thank you - using your example, I have the following 
      #! / usr/bin/perl -w

use strict;
use warnings;

use POSIX 'strftime';

my $nm = strftime('%Y', localtime).".txt";

my $filename = 'Facs_Data.txt';
open my $fh, '<', $filename
    or die "Couldn't open '$filename': $!";

my @lines = map  { /:([^\s]+)/ ? $1 : () } # take the stuff between th
+e : and the first blank
            grep { /Acct:/ } <$fh>; # Read a file line by line and sel
+ect the lines matching Acct:
        my $outfile = $_."_"."$nm" for @lines ;
        print $outfile;
        #open (OUTFILE, ">$outfile");
# do whatever with the values in @lines
#print "$_\n" for @lines;
close($filename);

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      root@localhost:~/GoldenLFiles# perl facs.pl Use of uninitialized value $outfile in print at facs.pl line 17, <$fh> line 168801.

      If I comment the print $outfile to see the output I get the error above. What am I missing here? Thanks in advance
[reply]
[d/l]
                my $outfile = $_."_"."$nm" for @lines ;

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        This line will set/declare $outfile in a loop, which is unlikely to be what you want.

        Did you want a loop over @lines instead? Or did you want to take the first element of @lines?

        print sprintf "Have %d items\n", 0+@lines;

my $item = $lines[0];
my $outfile = $item . '_' . $nm;
print "$outfile\n";

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        I tried the following code with the input data in the __DATA__ section for convenience:

        #! / usr/bin/perl -w

use strict;
use warnings;

use POSIX 'strftime';

my $nm = strftime('%Y', localtime).".txt";

my @lines = map  { /:([^\s]+)/ ? $1 : () } # take the stuff between th
+e : and the first blank
            grep { /Acct:/ }
            <DATA>; # Read a file line by line and select the lines ma
+tching Acct:

print sprintf "Have %d items\n", 0+@lines;

my $item = $lines[0];
my $outfile = $item . '_' . $nm;
print "$outfile\n";

print $outfile;
#open (OUTFILE, ">$outfile");
# do whatever with the values in @lines
#print "$_\n" for @lines;

__DATA__

foo

Acct:123
Acct:456

bar

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        Note that you have a close($filename), which likely should be close($fh) in your code.

[reply]
[d/l]
[select]

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