Bash Script Knowledge Base

This article holds some notes about scriping in bash.

Siehe auch: Shell-Skript How-To (Linux)

General

A bash script starts in the first line with:

#!/bin/bash

Variables

Define variable MY_STR:

HW="Hello World!"

Read content of the variable and put it to the console:

echo $HW

Source: https://www.geeksforgeeks.org/bash-script-working-of-bash-variables/

Working with Dates

To extract year, month or day (among others) from the system date :

date '+%Y-%m-%d'

Hint: The plus sign is needed for a reason I cannot explain.

The previous output always refers to the present, which at the time of writing this was:

2025-09-29

To have it work on a different reference date use:

date -d '2025-12-24' '+%m/%d/%Y'

For further variables see https://man7.org/linux/man-pages/man1/date.1.html

Output:

12/24/2025

Save the output in a variable in a bash script and print it out and also print it out directly:

#!/bin/bash
MONTH=$(date '+%Y-%m')
echo "***$MONTH***"
echo "***$(date '+%m/%d/%Y')***"

Output as of the time of writing:

***2025-09***
***09/29/2025***

Check if Bash Script Received Parameters

Check if any arguments were passed to the script:

if [ $# -eq 0 ]; then
  echo "No arguments received"
else
  echo "Arguments received"
fi

$# contains how many arguments were passed to the script.

Check if first argument was empty:

if [ -z "$1" ]; then
  echo "Argument 1 empty"
else
  echo "Argument 1 is $1"
fi

The -z switch will test, if the argument passed is empty. If it is empty, then the expression resolves to true and the body of the if statement is executed.

Sources:

https://stackoverflow.com/questions/6482377/check-existence-of-input-argument-in-a-bash-shell-script

https://www.w3schools.com/bash/bash_conditions.php