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Shell Scripting

A shell script (.sh) can be used to submit a sequence of commands to terminal.

Video

The following video outlines the basics of shell scripting.

08:32: The first line of a shell script must be the shebang line, telling system which shell interpreter to use. The default shell interpreter can be found by running echo $SHELL in terminal. This will return something like /bin/bash.

10:36: Before running a shell script, you may need to give it execution permissions (this is similar to the CONDA python issue with kennedy).

13:00: A shell script can accept any number of parameters.

Example Script

Let's create an example script which accepts 3 parameters and prints them, as well as the file name, called example.sh (execution permission can be given through chmod u+x example.sh):

#!/bin/bash

#This program accepts 3 parameters and prints them
echo File Name: $0
echo Param 1  : $1
echo Param 2  : $2
echo Param 3  : $3

Running this script through ./example.sh p1 p2 p3 prints: 

Exec Name: ./example.sh
Param 1  : p1
Param 2  : p2
Param 3  : p3

Useful Commands

  • echo - Use to display the value of a variable e.g. echo $SHELL will display the value of SHELL.
  • export var=5 - this will mean that an environmental variable called var will be created and given the value 5. It can then be accessed in terminal e.g. it can be printed through echo $var.
  • printenv - This displays all the environmental variables e.g. if the parameter SHELL shows up in the list, then its value can be accessed through $SHELL
  • source shell_script.sh - This will make all variables defined through export in the shell script shell_script.sh be available in the current terminal.