Evaluate Multiple Conditions in Bash "If" Statement [2 Ways] - LinuxSimply (2024)

Including multiple conditions within an if statement in Bash refers to evaluating several criteria simultaneously by combining them with logical operators AND and OR within a single if block. You can either use the single square brackets “[ ]” i.e. equivalent test operator or double square brackets “[[ ]]” with extended functionality to encapsulate all the conditions and perform a complex conditional check.

In this article, I will exemplify 2 ways to evaluate multiple conditions within an ‘if’ condition in Bash.

What is Compound “If” in Bash?

In Bash scripting, ‘compound if’ is a statement that includes multiple conditions within an ‘if’ statement. It uses the logical operators AND, OR, and compound conditionals all together.

This is useful when you have to execute a specific block of code based on the number of satisfied conditions. The basic structure of a ‘compound if’ statement is as follows:

if [ condition1 ] && [ condition2 ]; then#Code to execute if both conditions are truefi

Or,

if [ condition1 ] || [ condition2 ]; then#Code to execute if at least one condition is truefi

2 Methods to Use Multiple Conditions in Bash “If” Statement

To check multiple conditions in a Bash if statement, you can employ both [ ] and [[ ]] constructs. The following is a description of how you can assess multiple conditions by combining them either using a single construct or using individual structures in Bash ‘if’ statements.

1. Using Single Square Brackets “[ ]”

In Bash scripting, the single square brackets [ ] are considered as the equivalent test command that evaluates multiple conditions within an ‘if’ statement. In this case, the logical operators -a and -o can be used to combine all the conditions within a conditional expression where -a is a logical AND and -o is a logical OR.

To evaluate multiple conditions using -a and -o within one test alias, use the syntaxes as follows:

if [ CONDITION1 -a CONDITION2 ]; #True if both CONDITION1 and CONDITION2 are true.

if [ CONDITION1 -o CONDITION2 ]; #True if either CONDITION1 or CONDITION2 is true.

Here’s an example:

#!/bin/bash#Defining a variablevalue=20#Checking if a number is within a specified rangeif [ "$value" -lt 35 -a "$value" -gt 18 ]; thenecho "Number $value is within 18 and 35."fi

From the above image, you can see that multiple conditions are satisfied using -a within the “[ ]” construct.

Individual “[ ]” Construct for Each Condition

To evaluate multiple conditions within individual single square brackets [ ], use the syntaxes if [ CONDITION1 ] && [ CONDITION2 ]; and if [ CONDITION1 ] || [ CONDITION2 ];.

Following is an example indicating the usage of individual single square brackets to handle multiple conditions:

#!/bin/bashread -p "Enter your favorite color: " color#Checking if the entered color matches with the conditionif [ "$color" = "Black" ] || [ "$color" = "Blue" ] || [ "$color" = "White" ]; thenecho "Valid color entered."fi

The above snapshot is a clear demonstration of multiple conditional checks using individual “[ ]” with “||”.

2. Using Double Square Brackets “[[ ]]”

Using double square brackets [[ ]] with && (logical AND) and || (logical OR) helps in assessing multiple conditions within an ‘if’ statement.

To evaluate multiple conditions combined by && and || within one [[ ]] construct, use the syntaxes below:

if [[ CONDITION1 && CONDITION2 ]]; #True if both CONDITION1 and CONDITION2 are true.

if [[ CONDITION1 || CONDITION2 ]]; #True if either CONDITION1 or CONDITION2 is true.

Look into the following example:

#!/bin/bash#Defining two variablesclass="8"age=14#Checking if two conditions are metif [[ "$class" -le 10 && "$age" -ge 10 ]]; thenecho "Two conditions are met."fi

This image states two conditional checks using “[[ ]]” with “&&” where two conditions were satisfied.

Individual “[[ ]]” Construct for Each Condition

To assess multiple conditions within an ‘if’ statement, use double square brackets notation individually combining them with && and ||. For instance:

#!/bin/bashread -p "Enter a filename: " filename#Checking if one condition is metif [[ "${filename##*.}" = "txt" ]] || [[ "${filename##*.}" = "conf" ]]; thenecho "One extension is found."fi

This image illustrates the use of “[[ ]]” with “||” to evaluate multiple conditions.

Conclusion

To sum up, using multiple conditions within a Bash ‘if’ statement is a great way to test different scenarios of your scripts and make them more diverse and responsive.

People Also Ask

How can I check multiple conditions where at least one condition should be true?

You can use the OR (||) operator to check multiple conditions where at least one condition should be true.

Can I use variables to store conditions in Bash if statements?

Yes, you can use variables to store conditions and evaluate them within Bash ‘if’ statements. For example:

#!/bin/bash#Defining conditions in variablescondition1="-f /home/nadiba/to/local.txt" #Providing information in /path/to/file_namecondition2="-d /home/nadiba/to/Desktop" #Providing information in /path/to/directory#Checking if both conditions are metif [ "$condition1" ] && [ "$condition2" ]; thenecho "Both conditions are met.fi

How do I ensure correct evaluation order when combining multiple conditions?

To ensure correct evaluation order when combining multiple conditions, you can use parentheses that explicitly help in preventing issues encountered with condition precedence.

Can I use functions to encapsulate complex conditions for readability?

Yes, you can use functions to encapsulate complex conditions for better code structure and readability. For example:

#!/bin/bashfile_check() {local file_name=$1if [ -e "$file_name" ]; thenecho "'$file_name' exists."if [ -f "$file_name" ]; thenecho "'$file_name' is a regular file."elif [ -d "$file_name" ]; thenecho "'$file_name' is a directory."elseecho "'$file_name' is a special file."fielseecho "'$file_name' does not exist."fi}#Calling functionfile_check "color.txt"

Can I nest multiple if statements to handle complex conditions?

Yes, you can nest if statements to handle complex conditions. However, excessive nesting can make it difficult to read and keep track of the code. You can use logical operators AND and OR instead. Let’s see an example:

#!/bin/bashread -p "Enter your mark: " markif [ "$mark" -ge 30 ]; thenecho "You have passed the exam."if [ "$mark" -ge 50 ]; thenecho "You have a good grade."elseecho "It is a bad grade."fielseecho "You have failed the exam."fi

What’s the recommended approach for handling a large number of conditions?

When handling a large number of conditions, it’s recommended to use case statements or put the conditions in arrays to improve code maintainability. For example:

#!/bin/bashread -p "Enter a value from 1 to 5: " numbercase $number in1)echo "Valid number: One.";;2)echo "Valid number: Two.";;3)echo "Valid number: Three.";;4)echo "Valid number: Four.";;5)echo "Valid number: Five.";;*)echo "Invalid number.";;esac

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