Getting started

Updated 29 October 2024

Getting Started

Variables

bash
NAME="TRAW"

echo ${NAME}    # => TRAW :This prints the variable value
echo $NAME      # => TRAW :This prints the variable value
echo "$NAME"    # => TRAW :This prints the variable value
echo '$NAME'    # => $NAME : This will print the Exact string not value.
echo "${NAME}!" # => TRAW! :Concatenation of variable value with !

# Note: When declaring variables there should be no spaces between the variable
# name and equal sign and between the equal sign and the variable value.
# this will throw and error
NAME = "TRAW"   # => Error (about space)
It is crucial to keep in mind that when referencing a variable value, the dollar sign is used, but when referencing the variable to assign a value, the dollar sign is not used.

Special parameters

ParameterDescription
$1… $9Parameters 1 to 9.
$0Stores the name of the script file or the current shell name.
$1represents the first argument.
${10}Positional parameter 10.
$#Number of positional parameters
$*stores all the arguments.
$$Process id of the current shell.
$@All arguments, starting from first.
$-Current options.
$_Last argument of the previous command
$!The process ID (PID) of the most recently executed background pipeline (like started with command &)
$?Status of the most recently executed foreground-pipeline (exit/return code)
Learn more about special parameters here:

Comments

bash
# This is an inline Bash comment.
: '
This is a
Multi-line comment
in bash

If it looks very neat
'

# Note you can replace the single quoations with 
# double qoutations
For Multi-line comments use :' to open and '  to close.

Functions

bash
#!/usr/bin/env bash

get_username() {
    echo "TRAW"
}

# Or using the function keyword
function get_username() {
    echo "TRAW"
}

echo "You are $(get_username)"

Brace Expansion

Example Description
$ echo {A,B}.txtoutput will be A.txt and B.txt
{A,B}Same as A B
{1..5}Same as 1 2 3 4 5
Learn more about brace expansion here:

Example script

bash
#!/usr/bin/env bash

greet="world World"
echo "$greet!, I'm new here." 
# => Hello world! I'm new here.

#Execute the script

$ chmod +x helloworld.sh
$ ./helloworld.sh

# or just

$ bash helloworld.sh

Conditions

bash
#!/usr/bin/env bash

string="test"

if [[ -z "$string" ]]; then
    echo "String is empty"
elif [[ -n "$string" ]]; then
    echo "String is not empty"
fi

Command Substitution

bash
# => I'm TRAW
echo "I'm $(whoami)"

# Similar to:
echo "I'm `whoami`"
Learn more about command substitution here:
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