Your first Bash script

Introduction to Bash Scripting

Alex Scriven

Data Scientist

Bash script anatomy

A Bash script has a few key defining features:

It usually begins with #!/usr/bash (on its own line)
- So your interpreter knows it is a Bash script and to use Bash located in /usr/bash
- This could be a different path if you installed Bash somewhere else such as /bin/bash (type which bash to check)
Middle lines contain code
- This may be line-by-line commands or programming constructs

To save and run:

It has a file extension .sh
- Technically not needed if first line has the she-bang and path to Bash (#!/usr/bash), but a convention
Can be run in the terminal using bash script_name.sh
- Or if you have mentioned first line (#!/usr/bash) you can simply run using ./script_name.sh

An example of a full script (called eg.sh) is:

#!/usr/bash
echo "Hello world"
echo "Goodbye world"

Could be run with the command ./eg.sh and would output:

Hello world
Goodbye world

Each line of your Bash script can be a shell command.

Therefore, you can also include pipes in your Bash scripts.

Consider a text file (animals.txt)

magpie, bird
emu, bird
kangaroo, marsupial
wallaby, marsupial
shark, fish

We want to count animals in each group.

In shell you could write a chained command in the terminal. Let's instead put that into a script (group.sh):

#!/usr/bash
cat animals.txt | cut -d " " -f 2 | sort | uniq -c

Now (after saving the script) running bash group.sh causes:

   2 bird
   1 fish
   2 marsupial

Introduction to Bash Scripting