perl - how do i find out if a file doesn't contain a pattern?

mjays · #1 (**permalink**) 09-18-2007

how do i check a file for a pattern and perform an action if it doesn't exist?

i know how to search a file for a pattern. you just place it in an array like so.

Code:

#!/usr/bin/perl
my $data_file = "file.txt";
open DATA, "$data_file";
my @array_of_data = <DATA>;
        if ($_ =~ m/pattern/i) {
        print "\nfile contains pattern";
        }
close DATA

however, if you want to find out if a pattern doesn't exist, the search will always be true because each line is read separately and not all lines in the file contain the pattern.

how do search the whole file for the non-existence of the pattern?

hope i've made sense?

SanjayLinux · #2 (**permalink**) 09-18-2007

Perl regular expressions

[^something] matches any character except those that [something] denotes; that is, immediately after the leading “[”, the circumflex “^” means “not” applied to all of the rest

[^abc]+ any (nonempty) string which does not contain any of a, b and c (such as defg)

~~~Sanjay~~~

cbkihong · #3 (**permalink**) 09-18-2007

You can search the file for the pattern, and set a variable to a certain value when a match is found. If the variable is not assigned this value, then there is no match. Does that make any sense to you?

mjays · #4 (**permalink**) 09-18-2007

thanks guys.

i can use either of those ideas but cbkihong's will be easier to read.

bit annoyed that i didn't think of that myself. i've written loads of unix shell scripts using the 'set variable' method.

mjays · #5 (**permalink**) 09-19-2007

i've figured out a better solution.

i didn't know there was a 'grep' command until i curiously typed into google "perl +grep". i'm very new to perl by the way.

Code:

#!/usr/bin/perl
my $data_file = "file.txt";
open CHK_ARRAY, $data_file;
my @chk_array = <CHK_ARRAY>;
close CHK_ARRAY;
if (grep(/pattern/,@chk_array) eq 0) {
    print "\npattern not here!";
}

More UNIX and Linux Forum Topics You Might Find Helpful
Thread	Thread Starter	Forum	Replies	Last Post
HELP! PERL script to find matched pattern	kimhuat	Shell Programming and Scripting	1	05-12-2008 10:24 AM
Script to find file name for non matching pattern	sujoy101	Shell Programming and Scripting	5	03-31-2008 09:10 AM
find and replace a pattern in a file	krishnamaraju	Shell Programming and Scripting	1	08-29-2006 10:02 AM
Find script with input pattern file	iguanathompson	Shell Programming and Scripting	8	02-06-2006 06:23 PM
how to find the exact pattern from a file?	surjyap	Shell Programming and Scripting	7	12-05-2005 09:00 AM

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes	Rate This Thread
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode	Rate This Thread:


	Powered by