BASH – Login Counter

Disclaimer

The instructions/steps/scripts/methods given below worked for me running CentOS. It may very well work for you on other linux distributions, Red Hat-like or otherwise. Please note that if you decide to use these instructions on your machine, you are doing so entirely at your very own discretion and that neither this site, sgowtham.com, nor its author is responsible for any/all damage – intellectual or otherwise.

What is BASH and AWK?

BASH is a free software Unix shell written for the GNU Project. Its name is an acronym which stands for Bourne-again shell. The name is a pun on the name of the Bourne shell (sh), an early and important UNIX shell written by Stephen Bourne and distributed with Version 7 UNIX circa 1978, and the concept of being born again. BASH was created in 1987 by Brian Fox. In 1990 Chet Ramey became the primary maintainer. BASH is the default shell on most GNU/Linux systems as well as on Mac OS X and it can be run on most UNIX-like operating systems. It has also been ported to Microsoft Windows using the POSIX emulation provided by Cygwin, to MS-DOS by the DJGPP project and to Novell NetWare.

AWK is a general purpose programming language that is designed for processing text-based data, either in files or data streams, and was created at Bell Labs in the 1970s. The name AWK is derived from the family names of its authors — Alfred Aho, Peter Weinberger, and Brian Kernighan; however, it is not commonly pronounced as a string of separate letters but rather to sound the same as the name of the bird, auk. awk, when written in all lowercase letters, refers to the UNIX or Plan 9 program that runs other programs written in the AWK programming language. AWK is an example of a programming language that extensively uses the string data type, associative arrays (that is, arrays indexed by key strings), and regular expressions. The power, terseness, and limitations of AWK programs and sed scripts inspired Larry Wall to write PERL. Because of their dense notation, all these languages are often used for writing one-liner programs. AWK is one of the early tools to appear in Version 7 UNIX and gained popularity as a way to add computational features to a UNIX pipeline. A version of the AWK language is a standard feature of nearly every modern UNIX-like operating system.

The Script

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#! /bin/bash
# 
# Displays the number of login attempts by users
# Gowtham, 2005.09.23
 
echo
echo " `hostname` login attempts by users in this month"
echo
last | awk '{print $1}' | sort | uniq -c | sort -nr