Posts Tagged ‘script’

Awk is a useful language for many command line tasks. Often awk is used on the command line on its own or with strings piped to it, but it is possible to turn that awk code into an executable script. Consider the following script. This file contains awk code with a shebang of awk -f. […]

Each user on a unix system is assigned a user id, or uid. You can see your uid by running ‘id -u’. root will have a uid of zero. So to check if the user running a script is root, you can simply check that id -u is equal to zero, like so: if [ […]

If you’ve got a string of items in bash which are delimited by a common character (comma, space, tab, etc) you can split that into an array quite easily. Simply (re)define the IFS variable to the delimiter character and assign the values to a new variable using the array=($<string_var>) syntax. The new variable will now […]

Min and max functions in Perl

Posted: 1st February 2012 by Tim in Perl
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Min and max functions are available in perl, but you need to load them first. To do this, add use List::Util qw[min max]; to the top of the script. These functions take a list of numbers and return the min/max of that list. The list can have 1 number or 100 – it doesn’t matter: […]

If you’re writing a website in PHP, then by each PHP script will time out after a set time (usually 30 seconds by default). If this happen, you’ll see an error like the following: Fatal error: Maximum execution time of 30 seconds exceeded in <file> on line <line> This is a safety feature; if your […]

If you’re writing functions in postgres then you’ll probably be using a language such as plpgsql. Let’s say you’re writing a script to to add all of these functions to a new database, but you don’t know whether that language has been created yet. You’ll probably want to do something like CREATE LANGUAGE IF NOT […]

Substrings in Bash

Posted: 17th October 2010 by Tim in Bash
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There are a number of ways to extract parts of a string in bash. If you know the position of the substring you’re looking for, then you can use the ${string:offset[:length]} syntax. This works by providing a string, an offset (or starting position – remember that the first letter is in position 0) and, optionally, […]

In Bash you quite often need to check to see if a variable has been set or has a value other than an empty string. This can be done using the -n or -z string comparison operators. The -n operator checks whether the string is not null. Effectively, this will return true for every case […]

CVS is annoying in that if you want to find out which files have been modified or need updating, you can’t simply use the cvs status command as there’s too much information displayed. In order to make it useful, you really need to filter the output. Note: the following tutorial only works for linux computers […]

There is no way to delete a folder in CVS like you can with files. The directories must be kept so that the versioning information relating to the files which used to be in the repository can still be used (ie: you can revert back to a revision when the files still existed). The only […]