PerlScripting < Main

see also:

RegularExpressions for more specifics on Perl regular expressions
this link for a basic class
Quick and dirty tutorial
all the O'Reilly books online for free?!?

Scan a string for email addresses
Strip out selected lines from a string
How to validate a kredit kard
How to parse command line options
How to recursively get all files starting in a directory
How to do file uploading via perl
Perl Switches
Doing a global file substitution (example: perl -p -i -e 's/from/to/g' filename)
Writing to a file
Reading from a file line by line
Reading from stdin
Checking if a variable is defined

Scan a string for email addresses

Say you have a web page, loaded into the variable theFile, and want to find all email links, and put them into an array...

foreach( split( /\n/, $theFile ) ) {

# note, the $_ variable, the element for each iteration of
#  foreach is implied in the regex substitution statement below

# Find all email addresses
    if (s!(([a-zA-Z0-9_\-\.]+)@((\[[0-2]{1}[0-5]{1}[0-5]{1}\.[0-2]{1}[0
-5]{1}[0-5]{1}\.[0-2]{1}[0-5]{1}[0-5]{1}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}
|[0-2]{1}[0-5]{1}[0-5]{1})(\]?))!$1!i) {

# Stick each in an array
        push(@names, $1);
    }
}

# Remove duplicates - weird but effective way
@uniq = sort keys %{ { map { $_, 1 } @names } };

Strip out selected lines from a string

Now, I'm sure there's a better perl 1-liner way to do this, but here I split the string line by line, and if the line is wanted, I stick it in a new string. I got a 1-liner regex substitution to almost work, but couldn't prevent it from sticking in blank lines for the unwanted lines.

foreach( split( /\n/, $changesIn ) ) {
    if (m!^$theTopic!g) {
        $changes = "$changes$_\n";
    }
}

How to validate a kredit kard

http://argentavis.hypermart.net/perl/ccvalidation.html

How to parse command line options

#!/usr/bin/perl

use strict;
use Getopt::Std;

our($opt_w, $opt_h);
getopts('hw:');

# no-parameter switch
print "doing help dump\n" if ($opt_h);

# parameter switch
if ($opt_w) {
  print "got $opt_w: for 'w' switch\n";
} else {
  print "no 'w' switch\n";
}

How to recursively get all files starting in a directory

How to do file uploading via perl

see http://www.webmasterbase.com/article/474

Perl Switches

-w	use warnings
-e	the next arg is the script to run (e.g `perl -e 'print "hello world\n"'` )
-p	walks through the file argument (?) see 'global file substitution' example

Doing a global file substitution (example: `perl -p -i -e 's/from/to/g' filename`)

Writing to a file

# the '>' indicates I want to write to the file
open(theFile, ">dump.txt")  || die "can't open the file"; 
print theFile "I've written to the file!\n";
close(theFile);

Reading from a file line by line

Note the <> construct when blank meant from stdin. Now, it means from the open file handle.

open(theDict, "/usr/share/dict/linux.words") || die "Can't open dict\n";

while (<theDict>) {
        print;
}
close(theDict);

Reading from stdin

Examples to read in each line and print it out, pre-pended with a -*

`while ($line = <>) { print "-*$line"; }`	basic example, but we can be more succint
...or simpler: `while (<>) { $_ =~ s!^!-*!; print $_; }`	works because `$_` means 'current line read from <>
...or simpler still: `while (<>) { s!^!-*;!; print; }`	works beacuse `$_` is assumed in the `print` and the substitution

Checking if a variable is defined


# '$/' is the Optional 'chunk mode' parameter.  Designates what the <> operator
#  looks for to terminate each read operation.  Default is '\n' (??)
$/ = "\n";

while (1) {
        if (not defined($junk)) {
                print "not defined\n";
                $junk = "junk";
        } else {
                print "now it's defined\n";
                last
        }
}

-- MattWalsh - 15 Aug 2002

Topic revision: r8 - 25 Aug 2005 - MattWalsh