How to use if condition in shell scripting

How to use if condition in Shell scripting?

In this article, we will see shell decision-making in Unix. While writing a shell script, there may be a situation when you need to adopt one path out of the given paths. So you need to make use of conditional statements that allow your program to make correct decisions and perform the right actions.


Unix Shell supports conditional statements that are used to perform different actions based on different conditions. We will now understand decision-making statements here −





if...else statement

If else statements are useful decision-making statements which can be used to select an option from a given set of options.

Unix Shell supports following forms of if…else statement −

if...fi statement
if...else...fi statement
if...elif...else...fi statement


#! /bin/bash

#To setup if statement and condition

if [ condition ]
then
    statement
fi

count=10
    if (( $count > 11 ))
then
    echo  "condition is true"
    else
    echo "condition is false"
fi

word=a
if [[ $word < "b" ]]
then
    echo "condition is true"
    else
    echo "condition is false"
fi 

word=a
if [[ $word == "b" ]]
then
    echo "condition is true"
    elif [[ $word != "a" ]]
    then
    echo "condition is false"
    else
    echo "condition will be true"
fi

#To check file and directory is exist or not  such as -e  file, -f file, -d directory,-b blog file such as video, -c  charectpr, -s size, -l, -r ,-w, -x

echo -e "Enter the name of the file : \c"
read file_name

if [ -s $file_name ]
then
    echo "$file_name found"
else
    echo "$file_name not found"
fi

#! /bin/bash
#it is logical and value where both condition should be correct if any one condition will be wrong so get false outcome

age=60
if [ "$age" -gt 18 ] && [ "$age" -lt 70 ]
then
    echo "valid age"
    else
    echo "unvalid age"
fi 

age=60
if [ "$age" -gt 18 ] && [ "$age" -lt 59 ]
then
    echo "valid age"
    else
    echo "unvalid age"
fi





#It is logical or value where anyone or both condition should be correct

age=60
if [ "$age" -gt 18 ] || [ "$age" -lt 59 ]
then
    echo "valid age"
    else
    echo "unvalid age"
fi

people=100
if [ "$people" -lt 50 ] && [ "$people" -gt 51 ]
then
    echo "total number of people correct"
    else
    echo "total number of people not correct"
fi 

people=100

if [ "$people" -lt 101 ] && [ "$people" -gt 51 ]
then
    echo "total number of people correct"
    else
    echo "total number of people not correct"
fi

people=100

if [ "$people" -lt 100 -o "$people" -gt 51 ]
then
    echo "total number of people correct"
    else
    echo "total number of people not correct"
fi