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In this article, we will explain string comparison in Bash using if statement.

The shell program that runs in Linux and provides a command line interface for users to execute different commands is called Bash shell. It is also used as the default shell in many Linux distributions and is called GNU Bourne-Again Shell (Bash).

Bash scripts

A series of Bash commands written in a file is called a Bash script. The Bash shell executes these commands after reading the file.

The file extension for a Bash script is .sh. The following contents of a file named First.sh are shown below.

#!/bin/Bash
echo "Hello World"

The above file First.sh is a Bash script that contains only one echo command, which displays Hello world on the terminal.

#!/bin/BashThe first line of the file tells the Bash program on your system to act as an interpreter and run the commands written in the script file.

Bash shell provides different methods to execute scripts on the terminal. Some of the methods are discussed below.

1. The bash command followed by a Bash script file is used to execute the script. The following command runs the First.sh script.

   bash First.sh
   

   The output of this command is:

   Hello World
   

2. Run the Bash script by specifying the path. chmod +x First.shAfter giving the script file executable permissions using , we can run the script file by specifying the path of the script.

   <path to the script file>/First.sh
   

   We can run the script using the above method using the absolute path or using the relative path of the script ./First.sh.

String variables in Bash

We can use the assignment operator (=) in Bash scripts to declare and initialize any string in a variable.

For example:

#!/bin/Bash
S="Hello World"
echo $S

In the above example, we have declared a string variable S and initialized it with Hello World as the value. The echo command uses the echo command and the $ operator to display the value of the string variable on the terminal.

String comparison operators in Bash scripting

We can use = (equal to) operator in Bash script to compare two strings. We also use ==operator to compare strings.

==Is a synonym for the = operator for string comparisons.

For example, consider a Bash script First.sh with the following contents.

#!/bin/Bash
S1="Hello World"
S2="Hello World"
if [ "$S1" = "$S2" ]
then
    echo "Equal"
else
    echo "Not Equal"
fi

The following script contains two strings, S1 and S2, that have the same value. The if condition uses the = operator to compare the strings; however, we can also use if [ "$S1" == "$S2" ]the statement to compare these strings.

Following is the First.sh script output.

Equal

!=The (not equal to) operator is used to match if two strings are not equal. We can use if [ "$S1" != "$S2" ]this operator in if statements.

This statement returns true if the strings S1 and S2 are not equal.