Pravar Agrawal Technology & Travel

Amazing Bash Script Options


Linux has become the de-facto operating system these days especially for servers. Most of us have been using Linux operating systems almost every day and it has become a need to understand this OS from it’s very basic to it’s core. Though there are many tutorials, posts available online which could help us in learning more about Linux, in this post I’ll be discussing few not so popular and some very common syntax being used for bash scripting.

Bash script begins

In majority of the bash scripts you might have read or maybe written, the below three lines:

set -o errexit
set -o pipefail
set -o nounset

set -o errexit is also equal to set -e which means that if in case any of the commands in our bash script fails, the entire script’s execution will fail. This option is very help to be used when you have multiple scripts running as part of automation or delivery pipelines.

set -o pipefail is used to exit out of your script if any of the pipe commands fail during the bash script’s execution. Or else you’ll be greeted with wrong exit codes when the code is being piped.

set -o nounset is also equal to set -u which means that the script will exit if any of your variables are not set.

Using pushd and popd commands

Often times, you would’ve seen two commands pushd & popd being used in any of the bash script ( example). These two commands are shell builtins which allows to manipulate the usage of directory stack. These are used to change the directories and return to the same whenever required. Let’s say we are currently in a directory called k8s_practice,

$ pwd

Now, I’ll pushd to another directory called git-clones,

$ pushd ~/git-clones
~/git-clones ~/k8s_practice
$ pwd

And upon using popd, we can simply pop the present directory and will return to the previous k8s_practice dir,

$ popd
$ pwd

These commands are very useful when you plan to quickly change between directory stack in your bash script.

Beyond infinity: /dev/null

I bet you’d have seen the following syntax: in many bash scripts,

» /dev/null 2>&1

This syntax is basically a shorter way of silencing a process. One can even write it as: 2>&

» /dev/null redirects standard output (stdout) to /dev/null, which eventually discards it. /dev/null is that dark place (special file) of linux OS such that whatever is written into it, is eventually discarded into void or sent into a black hole. And, 2>&1 redirects standard error to standard output which eventually discards it. & here indicates a file descriptor as there are three - standard input, output and error.

So, these were few basic pointers which I hope you’ll keep in mind or maybe pay attention to while writing your next bash script.