Getting Started

Variables

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)

<aside> 💡 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.

</aside>

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)

<aside> 🔗 Learn more about special parameters here:

</aside>

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**

<aside> 💡 For Multi-line comments use :' to open and ' to close.

</aside>

Functions

#!/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}.txt`	output will be A.txt and B.txt
`{A,B}`	Same as A B
`{1..5}`	Same as 1 2 3 4 5

<aside> 🔗 Learn more about brace expansion here:

</aside>

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 TRAW
echo "I'm $(whoami)"

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

<aside> 🔗 Learn more about command substitution here:

</aside>