You don't have to be writing Perl scripts to run complicated web sites do use Perl effectively. Learning just a few one-liners can help you a lot when you're running a Linux system.

get current GMT with perl

This one liner will get you the current Greenwich Mean Time:

perl -le "print scalar gmtime time"

use perl like sed

sed is a command line program that's an old standby on Linux systems. It's primarily used to change text files by way of the command line. With Perl you can do the same and with less typing!

Imagine you had a text file with a line: 'this is the summer of our discontent'. You could change 'summer' to 'winter' very easily, like so:

perl -pi -e 's/summer/winter/g' file

This will overwrite that file, so if you'd rather have a backup, then do this:

perl -p -i.bak -e 's/summer/winter/g' file

and the original file will now become file.bak. This trick also works on multiple files using wildcards.

add new line to a file ... if there's space

You can use perl to add a line to file. The following adds the text 'this is important information' to line 5 of the file but only if that line is blank.

perl -ple 's//this is important information/ if $. == 5; close ARGV if eof' file > newfile

change files to lowercase

At times, people send us files from different systems. The file names may be in all UPPERCASE letters and you might want to change them to lowercase. This perl one-liner will do that for you:

Go to the directory with the files and issue this command:

perl -le 'rename $_, lc( $_ ) foreach <*>'

By substituting 'lc' for 'uc', you do the reverse.

create random password

It's always a good idea to have very secure passwords. This Perl command will output 8 random characters that will be a good secure password, though probably not easy to remember.

perl -le 'print map { (a..z,A..Z,0..9)[rand 62] } 0..pop' 7

install CPAN modules

You don't have to a be a Perl guru to need to install Perl modules. A module is an add-on to Perl. These add-ons are there so developers don't have to reinvent the wheel, so to speak. Some very common programs make use of modules and without them, you won't be able to use them. Here's a basic explanation of installing Perl modules. We'll be getting them from CPAN, the Comprehensive Perl Archive Network.

First, in an xterm or terminal, open a CPAN shell

perl -MCPAN -e shell

The first time, it will ask you to configure it. If you want automatic configuration, just answer [no]. This will probably not have any ill effects.

Then you can install Perl modules like so

install Module_name::Bla.pm

If you have problems reaching the default site, use a search engine to look up a CPAN mirror. Then, in the CPAN shell, enter the mirror like so:

o conf urllist push ftp://ftp.someplace.org/mirror/CPAN/

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