Getting started¶

Variables¶

NAME="Bob"

echo ${NAME}    # => Bob :This prints the variable value
echo $NAME      # => Bob :This prints the variable value
echo "$NAME"    # => Bob :This prints the variable value
echo '$NAME'    # => $NAME : This will print the Exact string not value.
echo "${NAME}!" # => Bob! :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 = "Bob"   # => Error (about space)

Comments¶

# 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**

Functions¶

#!/usr/bin/env bash

get_username() {
    echo "Bob"
}

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

echo "You are $(get_username)"

Brace Expansion¶

Example	Description
$ echo {A,B}.txt	output will be A.txt and B.txt
{A,B}	Same as A B
{1..5}	Same as 1 2 3 4 5

Special parameters¶

Parameter	Description
$1… $9	Parameters 1 to 9.
$0	Stores the name of the script file or the current shell name.
$1	represents 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)

Example script¶

#!/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¶

#!/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¶

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

# Similar to:
echo "I'm `whoami`"

Last update: February 14, 2023