Useful Bash!


The tutorials assumes:

  • Ubuntu 16.04




This chapter shows you the basics of how to move around a terminal, how to create a bash script, how to run a bash script, and how to alias the bash script (first temporarily, and then permanently).

How to move around

Use cd to get back to your root directory

Use cd .. to traverse one directory back

Use cd DIRECTORYNAME to enter that directory

Use ls or ls -l to display the directory content

Use cd DIRECTORYNAME/SUBDIRECTORYNAME to traverse to a specific directory from the current working directory

Use cd /ROOTDIRECTORYNAME/DIRECTORYNAME/SUBDIRECTORYNAME to traverse to a specific directory from the root directory

How to get your current directory


Creating a script

sudo nano /#@PATHNAME@#/#@SCRIPT@#

After running the nano command we can start editing our script.

The script

A simple script to start with is outputting some text, let’s start by echoing ‘Hello World!’

Before we get to that we need to fulfill a requirement of any bash script, the #!/bin/bash at the start of the script.

  1. Add #!/bin/bash to the top of the file.
  2. Add echo "Hello World!" to the second line.

Hit CTRL+X, Y, and ENTER to save the script.

Download the script here

Making the script executable

chmod +x /#@PATHNAME@#/#@SCRIPT@#

Running the script


Making aliases

alias #@ALIAS@#='. /#@PATHNAME@#/#@SCRIPT@#'

The “.” marks the script for execution.

By running that in the command line we create the ‘#@ALIAS@#’ alias which will execute the #@SCRIPT@# via its’ full path.

Using the alias


Using command-line parameters

User input typed after the script call can be accessed by the dollar sign, an example:

We create the following script:

echo "The answer to the question of $2 is $1."

Which will output “The answer to the question life is 42.” if called as follows:

#@ALIAS@# 42 life

Download the script here

Making the alias permanent

Once you terminate your SSH session your alias is lost. The alias can be made permanent by altering the “bashrc” file.

The file is located at ~/.bashrc, you can edit it using any text editor.

sudo nano ~/.bashrc

Here is a link to a default bashrc file as example

As you can see in the example aliases are defined on a new line, regardless the place.

  # some more ls aliases
  alias ll='ls -alF'
  alias la='ls -A'
  alias l='ls -CF'

So if we want to make our alias persistent we need to add

alias #@ALIAS@#='. /#@PATHNAME@#/#@SCRIPT@#'

anywhere in the file - as long as it is on a new line.

After saving the file using CTRL+X Y ENTER we need to run our bashrc file

. ~/.bashrc

Which finalizes our changes without having to terminate and reconnect our session.

A better way!

So now we have seen how to add the alias to the bashrc file, however it would be better to keep these aliases in a seperate file. Firstly because it is easier to edit, and secondly because it is awesome for portability. If you have certain aliases you use a lot, push the file to version control and keep access to it even on other systems.

We need to uncomment or add the following code to reference our not-yet-created bash_aliases file.

  if [ -f ~/.bash_aliases ]; then
  . ~/.bash_aliases

Which simply states that if the bash_aliases file is found, run the bash_aliases file - effectively including aliases created in the bash_aliases file.

Create the bash_aliases file

sudo nano ~/.bash_aliases

Copy the following code block (when in clipboard, rightclick on terminal editor window) and save the file (CTRL+X, Y, ENTER).

  # Bash alias definitions
  alias #@ALIAS@#='. /#@PATHNAME@#/#@SCRIPT@#'

After adding an alias we need to run the bashrc file.

. ~/.bashrc

From now on aliases defined in the bash_aliases file are permanent.

A good alias to add secondly is the one for rerunning the bashrc file

sudo nano ~/.bash_aliases

Add the following line:

alias updatealiases='. ~/.bashrc'

Save the file (CTRL+X, Y, ENTER).

Use . ~/.bashrc for the last time and you are ready to add more aliases.

Now, when you add a new alias you only have to run the updatealiases command.

Executing aliases periodically

Sometimes you want a script to run at certain times, in this case we do not even have to reference the script - but simply use the alias.


Start editing your cron configuration by running crontab -e.

  The time and date fields are:

         field          allowed values
         -----          --------------
         minute         0-59
         hour           0-23
         day of month   1-31
         month          1-12 (or names, see below)
         day of week    0-7 (0 or 7 is Sunday, or use names)

An example cron command would be:

0 1 * * * . /#@PATHNAME@#/#@SCRIPT@#

(remember the . is part of the command because it says execute the script at the following path.)

<minute> <hour> <day_of_month> <month> <day_of_week> <command>

  0                                   |                minute
  1                                   |                hour
  *                                   |                any
  *                                   |                any
  *                                   |                any
  /#@PATHNAME@#/#@SCRIPT@#          |                command

This script runs on the 0th minute, every 1 hour, on any day, any month, and any day of the week. In other words, every hour, forever.