in reply to search and extract lines which contain a word

On a unix system: 
grep 'gateway' infile > outfile

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On a unix system: 
perl -ne'print if /gateway/' infile > outfile

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On a Windows system: 
perl -ne"print if /gateway/" infile > outfile

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An example using file handles: 

# Usage: script.pl infile outfile
# or
# Usage: perl script.pl infile outfile

use strict;
use warnings;

my ($qfn_in, $qfn_out) = @ARGV;

open(my $fh_in, '<', $qfn_in)
   or die("Unable to read file \"$qfn_in\": $!\n");

open(my $fh_out, '>', $qfn_out)
   or die("Unable to create file \"$qfn_out\": $!\n");

while (<$fh_in>) {
   if (/gateway/) {
      print $fh_out $_;
   }
}

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Update: Fixed copy & paste error mentioned in reply.
Update: Must have been asleep! Fixed missing my mentioned in reply.

Replies are listed 'Best First'.
Re^2: search and extract lines which contain a word
by cdarke (Prior) on Mar 26, 2008 at 12:36 UTC
    Slight typo in the file handles code: 
    open($fh_out, '<', $qfn_out)

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    Should read:: 
    open($fh_out, '>', $qfn_out)

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Re^2: search and extract lines which contain a word
by rudder (Scribe) on Mar 26, 2008 at 14:52 UTC

    Note, when using strict, both $fh_in and $fh_out must have "my" in front of them in the calls to open.

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      I would argue that my should be there either way, but that Perl only detects the error when use strict; is missing.

      But that's debatable. Anyway, thanks. Fixed.

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Re^2: search and extract lines which contain a word
by m@cky (Initiate) on Mar 27, 2008 at 06:38 UTC
    Hi, perl -ne "print if /gateway/" infile > outfile This method works great! But how can search for multiple strings? E.g. I want to search for lines containing the string 'gateway' and 'TIMESTAMP' and extract the entire line if found. Please kindly advice, thank you!
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      Hi Experts, Forget my last question post. I've managed to get it done. Not sure if i got it done 'intelligently' though. =P Can anyone please advice on this instead? Based on the current code below, how do i EXCLUDE extracting lines that contain any of the array of names defined, although strings 'gateway' & 'timestamp' are found in the particular line? E.g. ## To exclude extracting lines with username 'andrew' ## dcndksckdsnckdc gateway jdscjscjsdh timestamp andrew dkcd 
      print "Specify full directory of logfile.\n"; 
$file = <STDIN>; 
chomp $file; 
 
print "\nIdentified file is $file\n"; 
print "Is this correct? (y/n)\n"; 
$confirm = <STDIN>; 
chomp $confirm; 
 
 
if ($confirm eq "y") { 
    print "\nCommencing work on $file.\n"; 
    workings(); 
} else { 
    print "Terminating program...\n"; 
     
} 
 
## Subroutine to open & read logfile 
sub workings {  
    print"In Subroutine workings now.\n"; 
    open (LOGFILE, $file); 
    print "Opening logfile...\n"; 
    open (OUT, ">>", 'D:\Temp\test.txt') or die "$!"; 
    print "Opening output file...\n"; 
    print "Checking for string GATEWAY...\n"; 
    while (<LOGFILE>) { 
        if (/gateway/) {  
            $count = $count + 1; 
            print OUT; 
            print "Extracting line ...\n"; 
        } elsif (/TIMESTAMP/) { 
            $count = $count + 1; 
            print OUT; 
            print "Extracting line ...\n"; 
        } 
    } 
    print "\nTotal of $count lines extracted.\n"; 
    close OUT;  
    close LOGFILE; 
} 
 
##Array to contain usernames 
@names = qw(mddinzam khairulz sawaikha caoyx jchew khamshae hartinib t
+eev xiaolh yettynm yussofyu leegm narayam karuppa doraira edanor raza
+liha sambanr jwong lamks linwb rashid ongsp ooisc mohdrosn);

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[d/l]

        That prints out the lines containing either or both of "gateway" and "TIMESTAMP". Your if is equivalent to 

                if (/gateway/ || /TIMESTAMP/) { 
            $count = $count + 1; 
            print OUT; 
            print "Extracting line ...\n"; 
        }

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        However, I was under the impression you want lines containing both. If you want the lines containing both, your if would look like 

                if (/gateway/ && /TIMESTAMP/) { 
            $count = $count + 1; 
            print OUT; 
            print "Extracting line ...\n"; 
        }

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        As for excluding the listed names, one way is to start by building a regex using one of the following two methods: 

        my ($exclude_re) = map qr/$_/,
                   join '|',
                   map quotemeta,
                   @names;

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        or 

        use Regexp::List qw( );
my $exclude_re = Regexp::List->new()->list2re(@names);

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        The just make sure the line doesn't match that regexp: 

                if (/gateway/ && /TIMESTAMP/ && !/$exclude_re/) { 
            $count = $count + 1; 
            print OUT; 
            print "Extracting line ...\n"; 
        }

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      perl -ne "print if /gateway/ && /TIMESTAMP/" infile > outfile

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[d/l]
      you can have multiple alternatives:

      if /(gateway|TIMESTAMP)/

      A paren around the collection of alternatives, a | between each alternative.

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