Bash Scripting on Aamnah - Frontend Web Developer

Reading multiple lines of input from Bash terminal

Fri, 29 Jul 2022 21:48:26 +0500

This came up when i was doing HackerRank challenges for Bash. The challenge called Compute the Average had the following problem statement:

Given N integers, compute their average, rounded to three decimal places. The first line contains an integer, N. Each of the following N lines contains a single integer.

My first attempt was to use read with the -r flag in a while loop to read all lines one by one and ignore the \ character used to break up lines.

Practical examples of install scripts written in Bash

Sun, 30 May 2021 17:47:09 +0500

Docker
Firebase CLI (has syntax highlighting too)
Hombrew

Append to a dconf list and avoiding duplicates with existing entries

Sun, 09 Aug 2020 20:05:39 +0500

I need to do this for a script i’m writing to add custom keyboard shortcuts. I get the existing list with

1gsettings get org.gnome.settings-daemon.plugins.media-keys custom-keybindings

['/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom0/', '/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom1/', '/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom2/']

and now i need to add new entries to it and avoid duplicates with any previous custom$ shortcuts.

1gsettings set org.gnome.settings-daemon.plugins.media-keys custom-keybindings "[<altered_list>]"

Adding values to an existing array

1arr=( "${arr[@]}" "new_element1" "new_element2" "..." "new_elementN")
2#Or
3arr+=( "new_element1" "new_element2" "..." "new_elementN" )

using command substituion

1CUSTOM_SHORTCUTS_LIST=$(gsettings get org.gnome.settings-daemon.plugins.media-keys custom-keybindings)
2# ['/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom0/', '/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom1/', '/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom2/']
3echo -e "\nCUSTOM_SHORTCUTS_LIST: \n${CUSTOM_SHORTCUTS_LIST}"
4
5NEW_SHORTCUTS_LIST="${CUSTOM_SHORTCUTS_LIST%]*}, 'blah']" # substituion
6
7echo -e "\nNEW_SHORTCUTS_LIST: \n${NEW_SHORTCUTS_LIST}\n"
8# ['/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom0/', '/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom1/', '/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom2/', 'blah']

Here are some way people have done this when creating Gnome Terminal themes

OSTYPE in Shell

Fri, 03 Jul 2020 00:00:00 +0500

OSTYPE

OSTYPE variable stores the value of the operating system type.

1echo $OSTYPE

linux-gnu # Ubuntu

zsh and bash values differ a bit.

bash

$ echo $OSTYPE
  darwin18

zsh

% echo $OSTYPE
  darwin18.0

You can use a glob to account for the inconsistency

if [[ $OSTYPE == darwin* ]]; then
alias flushdns='sudo dscacheutil -flushcache'
fi

Another code snippet from the virualmin install script

 1remove_virtualmin_release () {
 2  # shellcheck disable=SC2154
 3  case "$os_type" in
 4    "fedora" | "centos" | "rhel" | "amazon"	)
 5    run_ok "rpm -e virtualmin-release" "Removing virtualmin-release"
 6    ;;
 7    "debian" | "ubuntu" )
 8    grep -v "virtualmin" /etc/apt/sources.list > "$tempdir"/sources.list
 9    mv "$tempdir"/sources.list /etc/apt/sources.list
10    ;;
11  esac
12}

uname -s

-s prints the kernel name

Checking operating system in a bash script and installing different programs

Sun, 28 Jun 2020 00:00:00 +0500

Because i have multiple machines and use both Ubuntu and macOS, I often need to alter my commands to account for differences in commands. For example, to get colorized output for the ls command, Ubuntu would use the --color flag while macOS will use the -G flag. -G in Ubuntu is for --no-group, i.e. don’t print group names in long listing format. And i don’t want to write two different files for Ubuntu and macOS, i want to be able to use the same .dotfiles on both systems.

Batch rename filenames to snake_case

Thu, 21 Mar 2019 08:02:11 +0500

tl;dr

1sudo apt install rename
2
3rename 's/ /_/g' *.{jpeg,jpg,png} | rename 'y/A-Z/a-z/'

1ls # get all filenames in the folder
2ls *.{jpeg,jpg,png} # get all .png, .jpg or .jpeg files
3awk '{ print tolower($0) }' # turn everything lowercase
4sed 's/ /_/g' # replace all spaces with underscores
5ls *.{jpeg,jpg,png} | awk '{ print tolower($0) }' | sed 's/ /_/g' # get all image filenames in snake_case in Terminal output

1ls

'Army vet poor children.jpg'
'British Us Warships.jpg'
'First time loving a soldier Here’s the 101 you need .docx'
'Get in shape military way .docx'
 LIVE
'Monday Motivation Posts_'
'Move over marvel, there’s a real Iron Man in town .docx'
'Prince Harry Green Caps.jpg'
'Prince Harry rewards Royal Marines with Green Berets as training ends  .docx'
'Recruitment taining 2019 things to keep in mind.jpg'
'Recruitment training 2019 things to keep in mind .docx'
'Titans comes together – US, British ships perform joint training.docx'
'Tornado goes out in style.docx'
'Tornado goes out in style.jpg'
'UK Defence Forces top the charts for LGBT empowerment .docx'
'UK defence forces LGBT top charts.jpg'
'Waste no excuse to tell your someone special how much you love them.png'
'Womens day.png'
'Writing the blues away.docx'
'Writing the blues away.jpg'
'amry vet runs for poor children .docx'
 army_military_married_love_hand-74014.jpg
 desktop.ini
'fitness army.jpg'
 uploaded

1ls *.{jpeg,jpg,png} | awk '{print tolower($0)}' | sed 's/ /_/g'

ls: cannot access '*.jpeg': No such file or directory
army_vet_poor_children.jpg
british_us_warships.jpg
prince_harry_green_caps.jpg
recruitment_taining_2019_things_to_keep_in_mind.jpg
tornado_goes_out_in_style.jpg
uk_defence_forces_lgbt_top_charts.jpg
waste_no_excuse_to_tell_your_someone_special_how_much_you_love_them.png
womens_day.png
writing_the_blues_away.jpg
army_military_married_love_hand-74014.jpg
fitness_army.jpg

Loop it through and rename all image files..

Write a Bash Function to Create a gruntfile.js for your project

Fri, 13 Jul 2018 14:25:43 +0500

Here is how it works

Everyt time i type gruntfile in the Terminal, it creates a gruntfile.js for me in the folder i am in. The resulting gruntfile.js has the following template code:

 1module.exports = function (grunt) {
 2  grunt.initConfig({
 3    pkg: grunt.file.readJSON('package.json'),
 4
 5    // CONFIG
 6  })
 7
 8  // PLUGINS
 9  grunt.loadNpmTasks('')
10
11  // TASKS
12  grunt.registerTask('default', ['', ''])
13}

I can now add my Grunt config to it.

What i have done is create a function gruntfile for me and saved in my .bash_profile so it is available to me anywhere in the Terminal.

Here Documents in Bash

Thu, 19 Apr 2018 00:00:00 +0500

tl;dr

a here document is special-purpose code block that you can use to feed commands

1ssh otherhost << EOF
2  ls some_folder; 
3  ./someaction.sh 'some params'
4  pwd
5  ./some_other_action 'other params'
6EOF

a limit string (usually EOF) indicates the start and finish of a here document. It doesn’t have to called EOF, you can call it whatever, e.g. JumanjiXYZ is a valid limit string
Variables inside a Here document need to be quoted or else they won’t be substituted, like so: "${VAR}"
The ending limit string needs to be at the beginning of the line

Here is an example where a here doc has been used to run multiple commands to the remote server. The script logs in to a remote server, takes a back up of all it’s databases and restores those databases directly on your current server, i.e. the server you ran the commands from

Upgrade to Bash 4 on macOS

Sun, 21 May 2017 00:00:01 +0500

 1# install Homebrew
 2# /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
 3
 4# install Bash via Homebrew
 5brew update && brew install bash
 6
 7# Add the new shell to the list of allowed (white-listed) shells
 8# sudo bash -c 'echo /usr/local/bin/bash >> /etc/shells'
 9echo "$(brew --prefix)/bin/bash" >> /etc/shells
10
11# Change to the new shell
12chsh -s $(brew --prefix)/bin/bash

sudo -i let’s you switch to root user
brew --prefix gives you the location of Homebrew install directory (/usr/local by default)
cat /etc/shells gives you the list of allowed shells

Associative Arrays in Bash

Sun, 21 May 2017 00:00:00 +0500

Associative arrays are key/value pairs, like Objects in JavaScript. You can iterate/loop over them.

create (declare) an associative array

This is done with the declare -A

1declare -A foo # declare an array
2declare -A foo bar baz # declare multiple arrays
3declare -A myArray=( [key1]=value1 [key2]=value2 [key3]=value3 ) # Initialise all at once

add values to the array

1foo[key]=value

Note the lack of spaces before and after the equal = sign

iterate over key/value pairs

The keys are accessed using an exclamation point: ${!array[@]}, the values are accessed using ${array[@]}

Directly run bash scripts in Github Gists locally in Terminal.

Mon, 13 Mar 2017 00:00:00 +0500

This post is about running install scripts saved in Gists on Github locally from a Mac Terminal using curl. However, this should work for just about any script saved online and is not in any way limited to gists.

You need to have Command Line Tools for Xcode installed.

Run a script off a Github Gist

First things first, find a script that you want to install. Here is a bash script that i wrote for installing WordPress.

Check if a program is installed

Mon, 30 Nov 2015 00:00:00 +0500

They key is in using hash or type to see if a command is available. For example, the output of

1hash nano

will change based on whether nano is installed or not. If nano is installed, you’ll get nothing. If nano is not installed, you’ll get an error.

So, we check for an error to see if something is not installed.

1command -v foo >/dev/null 2>&1 || { echo >&2 "I require foo but it's not installed.  Aborting."; exit 1; }

Batch renaming files in Bash

Fri, 17 Apr 2015 00:00:00 +0500

Use rename, which is a Perl script and maybe on your system already. You can use the rename command to quickly rename files using a regular expression pattern. For instance, if you wanted to rename all files containing foo to contain bar instead, you could use a command like this one:

1rename –v 's/foo/bar/g' *

How to rename multiple files based on a pattern

1for f in * ; do cp "$f" 2014-08-26-"$f" ; done

1mv $f ${f#[0-9]*-}

Test

How to create a man page for your Bash Script

Sun, 22 Feb 2015 00:00:01 +0500

The man pages are written as nroff files.
The /usr/local/man directory is the location typically used for any locally installed packages/files.
You can look at examples by looking at the existing manpages, (which will likely need to be uncompressed first), also read man.
Presently many users prefer groff to nroff, man groff to get started

Resources

Linux/UNIX Create a Manpage

How to take options for your Bash Script

Sun, 22 Feb 2015 00:00:00 +0500

Overview:

The distinction between options (flags) and positional args
getopts for short options, with : meaning “takes a value” and $OPTARG holding it
Manual while/case loop for long options (GNU getopt mentioned but not walked through)

Options are the flags you pass to a script, like -v or --verbose. Different from positional arguments ($1, $2, etc.) — options can come in any order, can be optional, and usually toggle behavior or carry a value.

Bash script to create a new Jekyll post

Sat, 21 Feb 2015 00:00:00 +0500

Getting Date

1# Date
2DATE=`date +%Y-%m-%d`

This will get today’s date in YYYY-MM-DD format.

Stripping spaces and replacing with underscores

1$ str="This is just a test"
2$ echo ${str// /_}
3This_is_just_a_test

Taking it Further

Make it a function

What’s cooler than a bash script? A bash function! With a function, we don’t have to specify script name/location every time. A bash function added to your .bash_profile will work globally anywhere in the Terminal. The command to run would then become like this:

Bash Scripts - Load/Read/Include Settings from Another File

Fri, 20 Feb 2015 00:00:00 +0500

To include a script into another script, we use the source command. In it’s simplest form, the command is this:

1source incl.sh

Here’s an example. Our keys.cfg file has this:

1AWSAccessKeyId="AKIAIKRGQQKRGQQKRGQQ"
2AWSSecretKey="UNYDSEUNYDSEUNYDSEmwMeIdQ6KRGQQv7dBdzDSE"

While our script.sh has this:

1#!/bin/bash 
2
3#Directory the script is in (for later use)
4SCRIPTDIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
5
6# Load the backup settings
7source "${SCRIPTDIR}"/keys.cfg

In our script.sh file we have sourced the file keys.cfg which contains configuration settings which we can now use.

Opencart Install Script

Tue, 17 Feb 2015 00:00:00 +0500

You can run this script directly using the following command

1curl -L https://gist.githubusercontent.com/aamnah/93cb63fc15e708649084/raw | bash

Here is the code, add this to your ~/.bash_profile and it’ll be available for you anywhere in the terminal.

Usage: To run just type opencart.

Bash script to create OCMOD and vQmod templates with a single command

Mon, 16 Feb 2015 00:00:00 +0500

OCMOD and vQmod are both modification systems for Opencart which allow you to change things without overwriting any core files. For Opencart version older than 2.x, vQmod was the king. With version 2.x Opencart launched it’s own modification system to replace the need for installing a separate extension.

The state Opencart is in right now, you’ll find yourself dealing with both vqmod and ocmod scripts. I know i do. So i have written this neat bash script which allows me to type ocmod foo to create a file called foo.ocmod.xml with the basic template ocmod. Same for vqmod, type vqmod bar and it’ll create a file called bar.xml with vqmod tempalte code.

Bash script to create Media Queries with Sass

Sat, 30 Aug 2014 00:00:00 +0500

The following bash script will create a main sass stylesheet style.scss and then create additional sass stylesheets for all devices (mobile.scss, ipad.scss, desktop.scss, wide.scss, iphone.scss) in a folder called media-queries.

In the end, we will combine stylesheets for all devices into one by importing them into our main style.scss.

I have divided the code for different devices in their own stylesheets becuase it keeps it is neat and organized and i prefer it that way. Sass does its magic and takes all the code from different files using @import and gives me one neat stylesheet. In the HTML, i only need to link to one stylesheet, the one that Sass generated for me.

Bash script to install a LAMP stack

Thu, 05 Jun 2014 03:31:41 +0500

The following script installs Apache, MySQL and PHP as well as PHPMyAdmin and some tweaks. For Debian based systems including Ubuntu. To install, copy the script to the server and run in the same folder you copied the file to by running the command:

1bash lamp.sh

Here is the script code:

View the Gist on Github