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perl script

How do I reverse lines of a file or files under Linux or Unix like operating systems?
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Linux / UNIX: Run Commands When You Log Out

I've written a Perl script that connects to our central server for me and it allows me feed data so that I make a timesheet later. How do I run my script when I log out from Apple OS X or Linux / UNIX workstation using bash shell?
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Howto: Write script in Perl

Q. I’m new to Linux and Perl. I’ve printed perl man page but it is bit confusing and omits a lot of simple things or details. Can you tell me how do I write a perl script? How do I open perl editor?

A. Larry Wall began work on Perl in 1987 and it is a dynamic programming language. Traditionally perl programs are written using text editor such as vi or emacs. The overall structure of Perl derives broadly from C.

Also when you start learning a new programming language, always start with Hello world program.

Hello world Perl Program

Let us print Hello world from a shell prompt. Type the following command (excluding $ ):
$ perl -e 'print "Hello, world!\n"';

Hello, world!

Let us write hello world program using vi text editor:
$ vi hello.pl
Append code as follows:
print "Hello, world!\n";

Save and close the file. Now setup a execute permission:
$ chmod +x hello.pl
Finally execute perl program:
$ ./hello.pl

  • First, I used the vi command to create a file named hello.pl
  • The first line of the script used to specify that the script is to be executed by perl program (#!/usr/bin/perl) and not by a shell.
  • Print command prints hello world on screen. Please note that the notation \n which stands for newline i.e. print a newline.

Further reading

This is just a simple introduction. You should consider following text books & resources for more information and mastering the perl:

Q. How do I find out RAM size / memory size in FreeBSD? How do I display amount of free and used memory in the system?

A. To displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel you need to install special script Most user use sysctal command to get all data. There is a perl script that automates everything and display back result on screen.

This script query the system through the generic sysctl interface. The sysctl utility retrieves kernel state and allows processes with appropriate privilege to set kernel state. You must have perl installed on FreeBSD.

FreeBSD command about RAM size and information

Download perl script which is written by Ralf S. Engelschall:

# fetch http://www.cyberciti.biz/files/scripts/freebsd-memory.pl.txt
# mv freebsd-memory.pl.txt /usr/local/bin/free
# chmod +x /usr/local/bin/free

Make sure perl is installed. Now to display or list total system memory usage type
$ free

mem_wire:          25341952 (     24MB) [  9%] Wired: disabled for paging out
mem_active:  +     47529984 (     45MB) [ 18%] Active: recently referenced
mem_inactive:+     15605760 (     14MB) [  6%] Inactive: recently not referenced
mem_cache:   +        16384 (      0MB) [  0%] Cached: almost avail. for allocation
mem_free:    +    165556224 (    157MB) [ 65%] Free: fully available for allocation
mem_gap_vm:  +       389120 (      0MB) [  0%] Memory gap: UNKNOWN
-------------- ------------ ----------- ------
mem_all:     =    254439424 (    242MB) [100%] Total real memory managed
mem_gap_sys: +      4988928 (      4MB)        Memory gap: Kernel?!
-------------- ------------ -----------
mem_phys:    =    259428352 (    247MB)        Total real memory available
mem_gap_hw:  +      9007104 (      8MB)        Memory gap: Segment Mappings?!
-------------- ------------ -----------
mem_hw:      =    268435456 (    256MB)        Total real memory installed
mem_used:          87257088 (     83MB) [ 32%] Logically used memory
mem_avail:   +    181178368 (    172MB) [ 67%] Logically available memory
-------------- ------------ ----------- ------
mem_total:   =    268435456 (    256MB) [100%] Logically total memory

Linux like free command for FreeBSD

Freecolor is a free replacement that displays free memory graphically as a bargraph. It supports the same options as free. Install freecolor, enter:
# cd /usr/ports/sysutils/freecolor
# make install clean

To see memory details, enter:
$ freecolor -m -o
Sample output:

             total       used       free     shared    buffers     cached
Mem:          4082        825       3256          0          0        117
Swap:         2048          0       2047

$ freecolor -t -m -o
Sample output:

             total       used       free     shared    buffers     cached
Mem:          4082        825       3256          0          0        117
Swap:         2048          0       2047
Total:        6130 = (     826 (used) +     5421 (free))

How do I read or display command-line arguments with Perl?
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How do I use sprintf() function in a perl script under Linux or UNIX?
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How do I send html email from Perl?

Q. How Can I send html email from cgi perl program under UNIX / Linux and Apache web sever?

A. Sending HTML email is an easy task with MIME::Lite CPAN module. It is a low-calorie MIME generator.

It can be use to send html emails, graphics file email attachments as a single-part or multi-part message. Here is simple perl script that sends html email.

Install Perl MIME::Lite

If you do not have MIME::Lite module, install using following command (login as a root user):

# cpan -i MIME::Lite

Perl script code

Script to send html email from perl:

#!/usr/bin/perl -w use strict; use MIME::Lite; # SendTo email id my $email = 'user@somewhere.com'; # create a new MIME Lite based email my $msg = MIME::Lite->new ( Subject => "HTML email test", From => 'YOU@somewhere.com', To => $email, Type => 'text/html', Data => '<H1>Hello</H1><br>This is a test email. Please visit our site <a href="http://cyberciti.biz/">online</a><hr>' ); $msg->send();

Save the script and execute it. Here is an email (sample) send by above script:

Read man page of MIME::Lite for more information:

perldoc MIME::Lite