Harish Kannarao harishkannarao

Bash Script loops and conditional statement example

The following blog post shows example of bash script with for loop, while loop, if elif else conditional statements.

Important aspects covered in the sample script:

Conditional while loop
While loop to iterate over lines in a file
Infinite while loop with break and continue
Infinite while loop with sleep
Iterate over arguments passed as input using for loop
For loop with counter

youtube-dl

youtube-dl is an opensource command line tool to download video or audio from online video streaming services.

Videos downloaded in mkv or webm extensions can be played by VLC Media player in all major devices and operating systems including iPhone, Android devices.

Tool website: https://youtube-dl.org/

This gist shows the example commands to use the tool and doesn't support or encourage piracy or violation of copyrights of the online streaming service or the author of the content

Installing youtube-dl:

Copy new files from source to target and skip files if it already exist in target

rsync --dry-run -avzurh --stats --delete --progress /tmp/source/ /tmp/target/

Explanation of flags:

-a -> Archive mode, preserve the file system properties
-v -> Verbose output
-z -> Use compression mode for data transfer, speeds up for transfer over network
-h -> Output in human readable format

Bash Script Example

The following blog post shows a sample bash script covering some inportant aspects in writing a bash script.

Important aspects covered in this script:

Validate if input arguments are passed
Parse positional arguments
Handle parameter values with white space
Validating the arguments (using regex)
While loop to iterate through varargs
Usage of unit functions

	#!/bin/sh

	# Make the script to abort if any command fails. Use set +e to change the behaviour and ignore failed command.
	set -e

	# Prints the commands as it is executed. Useful for debugging. Use set +x to disable debugging.
	set -x

	# Set default values
	ORGANISATION_NAME="${ORGANISATION_NAME:-com.example}"

	#!/bin/bash

	# Make the script to abort if any command fails. Use set +e to change the behaviour and ignore failed command.
	set -e

	# Uncomment below line to print the commands as it is executed. Useful for debugging. Use set +x to disable debugging.
	# set -x

	# Source the functions from an url
	source <(curl -s "https://gist.githubusercontent.com/harishkannarao/58d317f2743c842b5323165a492db81c/raw/75ee691d4d4568c59443a070c6e5d192d717b6bc/reusable_functions.sh")

	#!/bin/bash

	function add()
	{
	echo "$1 + $2" \| bc -l
	}

	function subtract()
	{
	echo "$1 - $2" \| bc -l

	#!/bin/bash

	# Make the script to abort if any command fails. Use set +e to change the behaviour and ignore failed command.
	set -e

	# Uncomment below line to print the commands as it is executed. Useful for debugging. Use set +x to disable debugging.
	# set -x

	echo "Example of numerical comparison with if elif else"
	for (( c=-5; c<=5; c=$c+1 ))

	#!/bin/bash

	# Make the script to abort if any command fails. Use set +e to change the behaviour and ignore failed command.
	set -e

	# Uncomment below line to print the commands as it is executed. Useful for debugging. Use set +x to disable debugging.
	# set -x

	while [[ $# -gt 0 ]]
	do