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Learning and Understanding Perl

Learning and Understanding Perl

Owned by Keith Sinclair (Deactivated)
Last updated: Mar 30, 2019

Introduction

You DO not need to learn Perl to use NMIS, Perl is however a powerful, elegant and thoughtful language for solving real problems.  You can do low level things like C with the ease of scripts like BASH, and everything in between.  BUT the real power of Perl is CPAN, the Comprehensive Perl Archive Network, someone somewhere has probably already solved your problem and published something on CPAN.

Perl Online References

Some great web pages to learn about Perl

Please comment if you know some more good ones.

Perl Basics

Perl Data Types

  • Scalar -> $variable
  • Array -> @array
  • Associative Array (hash) -> %hash
  • Combinations to make complex types easily (looks confusing but very powerful)
  • Array of hashes $array[$i]->{$key}
  • Hash of hashes $hash{$key}{$var}
  • Multi-dimensional $var->{$key}->[0]->{$thing}

Use it!

use strict;

Perl if statement

 

use strict;
my $string = "this is a string";
if ( $string eq "string" ) {
  print "$string is the same as \"string\"\n";
}
elsif ( $string =~ /string/ ) {
  print "regex match $string has \"string\" in it\n";
}
elsif ( $string == 100 ) {
  print "$string is the number 100\n";
}
else {
  print "Else Nothing\n";
}

Perl Loops -> While

while (condition) {
  # do something
}

Perl Loops -> for

use strict;
my @array = (1, 2, 3, 4, 5, 6);
for ( my $i = 0; $i <= $#array; ++$i ) {
  print “i=$array[$i]\n”;
}

Perl Loops -> foreach

use strict;
my @array = (1, 2, 3, 4, 5, 6);
foreach my $i ( @array ) {
  print “i=$i\n”;
}

Open a file and loop through

use strict;
my $match = "blah";
my $file = "textfile.txt";
my $lines = 0;
open (DATA, $file) or die "ERROR with $file. $!";
while (<DATA>) {
  chomp; # not necessary but gets rid of trailing spaces and newlines.
  if ( $_ =~ /$match/) {
    print "$lines: $_\n"; 
  }
  ++$lines;
}

 


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