[SOLVED] perl script cannot match the word with [ or ] character.

casualzone · 01-30-2012, 03:11 AM

hi

i have written a perl script to do text extraction & post-processing (matching etc).

I encounter a problem where my perl script cannot match the word with [ or ] character.
eg:
bit[0]
bit[1] etc
xxxxx[120]

the extracted word can be with or without the [ or ] character.

my syntax for match word:
if( $temp_pin =~ m/^@pin[$i]$/ )

acid_kewpie · 01-30-2012, 03:20 AM

escape the characters:

if( $temp_pin =~ m/^@pin\[$i\]$/ )

casualzone · 01-30-2012, 07:24 PM

@pin[$i] is an array, I am going to match the element in that array.
therefore, i dont thinkg "if( $temp_pin =~ m/^@pin\[$i\]$/ )" is a right way.
any opinion?

part of my code:
@split2 = split(" ", @file2[$line2]);
$temp_pin = shift(@split2)
if( $temp_pin =~ m/^@pin[$i]$/ )

Cedrik · 01-30-2012, 07:34 PM

Wow...

Code:

@split2 = split " ", $file2[$line2];
$temp_pin = shift @split2;

if ($temp_pin eq $pin[$i]) {
  ...

Or if you don't need @split2 later in your code, this can be shorten:

Code:

$temp_pin = (split " ", $file2[$line2])[0];

if ($temp_pin eq $pin[$i]) {
  ...

casualzone · 01-30-2012, 09:08 PM

thx for shorten the script. (i am still new to perl, i usually write perl in C-like language)

I am more concern how to handle the [] in my array element.

Cedrik · 01-31-2012, 04:31 AM

When you use:

Code:

if( $temp_pin =~ m/^something$/ )

It is equivalent to:

Code:

if ( $temp_pin eq 'something' )

You said you want to match the "element in that array"
So I thought you wanted to match the element value
Is it correct ?

chrism01 · 02-01-2012, 12:10 AM

Consider this code snippet

Code:

$var1 = "bit[20]";
$arr1[0] = "bit[20]";
if ( $arr1[0] =~ /($var1)/ )
{
    print "regex match\n";
}
if( $arr1[0] eq $var1 )
{
    print "str match\n";
}

With '[]' as part of the value you are trying to match , only the string comparison works.
Without the '[]' both work.
Note that the string comparison works with or without '[]' in the compared values.

Your Perl syntax generally bothers me:

Code:

# this is a Perl array
@pin;   

# this is the 'ith' element of the array
# a single value is always a scalar ($var), even if its an array element
# or a hash key/val eg $hash{$key} = $val, where %hash is the hash.
$pin[$i];

# cast an array ref ($i) stored inside an arr element ( $arr2[$i] )to an array
@arr1 = @{$arr2[$i]}

Can you clarify your code/data ?

casualzone · 02-01-2012, 02:42 AM

Code:

$var1 = "bit[20]";
$arr1[0] = "bit[20]";
if ( $arr1[0] =~ /($var1)/ )
{
    print "regex match\n";
}
if( $arr1[0] eq $var1 )
{
    print "str match\n";
}

now i know =~ & eq match are different.

chrism01 · 02-01-2012, 07:43 PM

Yep. If comparing "whole" values, use

1. eq for strings
2. == for nums (ints )
for floats you need to worry about rounding etc

Code:

# equal(NUM1, NUM2, ACCURACY) : returns true if NUM1 and NUM2 are
# equal to ACCURACY number of decimal places

sub equal {
    my ($A, $B, $dp) = @_;

    return sprintf("%.${dp}g", $A) eq sprintf("%.${dp}g", $B);
  }

3. only use regex if you want to match a (sub-)pattern rather than a complete value

http://perldoc.perl.org/
http://www.perlmonks.org/?node=Tutorials

Best practice is to start all Perl progs with

Code:

#!/usr/bin/perl -w
use strict;             # Enforce declarations

-w equiv to 'use warnings;'

You can also do

Code:

perl -wc prog.pl

which does a pre-flight check without executing the prog.

casualzone · 02-01-2012, 11:26 PM

thx a lot.
it is helpful for me as a beginner