"if" Statements in Shell/Bash

if statements are used in shell/bash scripting to control the flow of execution of the script based on certain conditions being met.

The basic structure of an if statement in shell/bash is:

if [ condition ]
then
    # code to be executed if condition is true
else
    # code to be executed if condition is false
fi

In this structure, the condition is an expression that is evaluated to either true or false. If the condition is true, the code inside the then block is executed, and if the condition is false, the code inside the else block (if present) is executed.

Here is an example showing the use of an if statement to check if a file exists:

if [ -f /path/to/file ]
then
    echo "File exists"
else
    echo "File does not exist"
fi

In this example, the -f option is used to check if the given file exists. If it does exist, the message "File exists" is printed; if it doesn't exist, the message "File does not exist" is printed.

Other common conditions used in if statements in shell/bash include:

• -d - check if a directory exists
• -n - check if a string is not empty
• -z - check if a string is empty
• -eq - check if two numbers are equal

Here's an example showing the use of if statements with some of these conditions:

if [ -d /path/to/directory ]
then
    echo "Directory exists"
else
    echo "Directory does not exist"
fi

if [ -n "$VAR" ]
then
    echo "String is not empty"
else
    echo "String is empty"
fi

if [ "$NUM1" -eq "$NUM2" ]
then
    echo "Numbers are equal"
else
    echo "Numbers are not equal"
fi

These examples should give you an idea of how to use if statements in shell/bash scripting to control the flow of execution based on various conditions.