Beefy Boxes and Bandwidth Generously Provided by pair Networks
laziness, impatience, and hubris

extracting data from an input file and associated errors

by rakshas (Novice)
on Feb 02, 2012 at 23:28 UTC ( #951557=perlquestion: print w/ replies, xml ) Need Help??
rakshas has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I have the following format of data in a text file. I can successfully read it from the file ___________________________________________________________
-rw-r--r-- 1 next users 2153 Jan 1 10:50 mytake_120.115.152.136.csv
I want to extract "" and use it so I wrote the following script.
use strict; use warnings; print "\nEnter the Model 1\n"; my $Model_Name1= <STDIN>; chomp $Model_Name1; open (DATA, "< C:/Perl_Scripts/InputFile.txt"); my @array_of_data = <DATA>; close (DATA); foreach my $line (@array_of_data) { if ( $line =~ m/\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\.csv$/g ) { print "Match $1"; } }
As I have said earlier, I want to extract "", hence I am using the regex. It just prints "Match" but also gives an error Use of uninitialized value $_ in pattern match (m//) at C:\Perl_Scripts\ line 31. Any Help will be much appreciated. Regards Vivek

Comment on extracting data from an input file and associated errors
Download Code
Replies are listed 'Best First'.
Re: extracting data from an input file and associated errors
by jwkrahn (Monsignor) on Feb 02, 2012 at 23:47 UTC
    open (DATA, "< C:/Perl_Scripts/InputFile.txt");

    You should verify that open worked correctly:

    open my $DATA, '<', 'C:/Perl_Scripts/InputFile.txt' or die "Cannot ope +n 'C:/Perl_Scripts/InputFile.txt' because: $!";

    my @array_of_data = <DATA>; close (DATA); foreach my $line (@array_of_data) {

    There is no need to read the entire file into memory first:

    while ( my $line = <$DATA> ) {

    if ( $line =~ m/\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\.csv$/g ) { print "Match $1"; }

    The pattern is anchored at the end of the line so the /g option is superfluous.    You are not using capturing parentheses in the pattern so there is nothing in $1 to print out.

Re: extracting data from an input file and associated errors
by chilledham (Pilgrim) on Feb 02, 2012 at 23:42 UTC

    You need to capture the match you want:
    $line =~ m/(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\.csv$/g

    The match in your first set of parens will be stored in $1, in the second set of parens in $2, and so on.
    See perldoc perlretut.

Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: perlquestion [id://951557]
Approved by toolic
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others making s'mores by the fire in the courtyard of the Monastery: (6)
As of 2015-12-01 03:41 GMT
Find Nodes?
    Voting Booth?

    What would be the most significant thing to happen if a rope (or wire) tied the Earth and the Moon together?

    Results (792 votes), past polls