Posts Tagged ‘terminal’

Accessing fields by index in Awk

Posted: 11th August 2015 by Tim in Awk
Tags: , , , , ,

In awk, fields are accessed by number; $1 for the first field, $2 for the second, etc. But sometimes the field number you want to access is not known until run time. In these cases, you can access the field using the $(<index>) syntax. The constant NF contains the number of fields available. For example, […]

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. […]

Linux Terminal Clock

Posted: 9th March 2015 by Tim in Bash, Linux
Tags: , , , , , , , , ,

Ever wanted to have a real-time clock on your linux terminal? We can create one with a single line of bash, like so: while echo -en “$(date)\r”; do sleep 1; done Let’s look at how this works: date is a common unix tool used to print the current date and time. The $(…) means that […]

With Docker, you can specify the command to run inside the container on the command line. But what if you want to run multiple commands? You can’t escape the && syntax, or wrap the command in quotes, as Docker won’t recognise it. The trick here is to use sh -c ‘<command1 && command2 [&& command3 […]

There are many ways in the linux terminal to print the nth word of a given file or output. One way to do this without worrying about tabs, extra spaces or word length is to use awk. With awk, this can be done on one line by using the {print $<n>} syntax. For example, the […]

If you have a HyperSQL (HSQL) database stored in a file, it is often useful to be able to query that database from the command line. This can be done using the following command: hsqldb-sqltool –inlineRc url=jdbc:hsqldb:file:<db_name>,user=<username>,password=[<password>] By default, user SA with no password will exist for each database file. If the database does not […]

Formatting a usb drive in linux

Posted: 11th July 2012 by Tim in Linux
Tags: , , , , , , , ,

So you’ve got a USB drive, and you need to reformat it. You can do this all quite easily on the command line using the fdisk utility. First, get the device location. This will be something like /dev/sdd. You want the location of the device, not a partition on the device ie: /dev/sdd instead of […]

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 […]

Sometimes in a terminal you want to strip out the first line of output from a command. For example, you may want to generate a list of users which have tasks running using the ps command. This command puts a header at the top of the output. You can remove this header by piping the […]

Ever jumped onto an Ubuntu server somewhere without knowing which operating system version it’s running? You can find this out with one simple command: lsb_release -a This will provide output like: Distributor ID: Ubuntu Description: Ubuntu 9.10 Release: 9.10 Codename: karmic

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 […]