How to Set Command Output to Variable in Bash [2 Methods]

In Bash scripting, storing the output of a command is a fundamental task. The task includes command substitution and variable assigning techniques. One can substitute commands using dollar signs or backticks. Later, assign the output to a variable. After assigning the variable, one can reference and utilize it throughout the script as needed. In this article, I will show you how to set the output of a command to a variable in Bash script.

2 Methods of Setting Output of Command to Variables in Bash Script

There are two common methods of setting the output of the Bash command into a variable. Command within a dollar sign or within a backtick is executed and stored in a variable.

You can read the Comparative Analysis of Methods to find the easy one for you.

1. Substituting Command and Set in a Variable Using Dollar Sign

In this first method, I will discuss substituting a Bash command using the dollar sign ($) and storing the output in a variable for further use in a script.

A. The Output of a Single Command

In the following example, I will store the output of the pwd command and use it later in the script. Let’s see the bash script for this:


echo "Your current directory: $dir"

This simple program echoes the current directory path that is stored in the dir variable. Previously, the pwd command is used to get the current directory path.

bash set output of command to variableThe output image shows the current directory as expected.

B. Command With Formatting

A Bash Command might have different options and arguments. The output of the command significantly varies based while using those options. In this script, I am going to show how to format command output with options and store the output in a variable. For that, write the following script:


today=$(date +"%d %B")  # Get today's date and store it in today variable

if [[ "$today" == "25 December" ]]; then
echo "Merry Christmas! Today is a special day of celebration!"
echo -e "Today is $today.\nEnjoy the day."

This script uses the date command to get the current date and stores the output in the today variable. The format of the date stored in the variable is defined using +"%d %B". Here, %d represents the day of the month, and %B represents the full month name.

The script then checks if today’s date is December 25th using the condition [[ "$today" == "25 December" ]]. If the condition is true, it echoes “Merry Christmas! Today is a special day of celebration!”.

If the condition is false, it executes the else block. The -e option enables the interpretation of backslash escapes to display a newline character between the two lines.

set variable to output of a command with option in BashWhen running the script it shows today’s date with the dd/mm format.

C. The Output of Multiple Commands With Options and Arguments

In Bash script, multiple commands can be used for various purposes in a single line. In this example, I will show you how to set the output of multiple commands in a variable. And later use that variable for more complex tasks.


count_files=$(find . -type f -print | wc -l)
echo "There are $count_files files in the current working directory."

empty_files=$(find . -type f -empty | wc -l)
echo " $empty_files of them are empty."

Here, the wc command initially counts the number of total files in the current directory when the output of the find command passes through it. The overall output is set to the count_files variable. Later, the -empty option of the find command counts the empty files of the current directory. Each time the number of counted files is echoed using the echo command.

 Set output of multiple command to a variable in BashWhen running the code, it shows the total files of the current directory and how many of them are empty.

2. Substituting Command and Set in a Variable Using Backtick

Command substitution using backticks (` `) is an older method to capture and store command output in a variable. The command within backticks is the desired command to execute and retrieve the output.

If our scripts have to be really portable on various Unix systems along with Bash or KornShell, it’s better to use backticks notation rather than the dollar sign. To explore further regarding command substitution using backtick, write the following script:


echo “The logged in user is: $current_user”

This script will execute whoami within backtick and store the output in the current_user variable. It echoed back the user name when executing the echo command.

Backtick substitution in BashThe image shows the current logged in user after successfully substituting the whoami command.

A. Multiline Command Substitution Using Backslash

Backslash is used for writing multiline commands in Bash script. To work on it open a file and write the following script:


info=`(grep -l\
-i -n -w\
"hidden" *.txt)`
echo $info

This will search for the word “hidden” (case-insensitive and whole word match) in all the .txt files in the current directory. It will then print the filenames of the matching files along with the line numbers where the word “hidden” is found. Here, slash (\) is used for each new line of command substitution.

Setting output of multiline command into a variable in BashThe output shows that there is a file named message.txt that contains the word hidden.

Note: Nested backticks often don’t work in Bash. Hence not recommended. For example, the following script will show an error.


`cat `(grep -l\
-i -n -w\
"hidden" *.txt)``

Issue of nested command substitution using backtick

The script shows an error due to the nested backtick that can not be executed.

B. Substituting Command With Path Name

Like substituting a command using its name one can easily substitute the command using its path name as well. To see how it works, open a file & write the following script:


echo “Current directory:$dirname”

This script prints the current directory. Initially, it substitutes the pwd command using the backticks and the pathname of the command. Later it echoed the current directory that is stored in the dirname variable previously.

Set output of a command to a variable using path of the command

Comparative Analysis of Methods to Set Command Output to Bash Variable

In this article, I have discussed two different methods of substituting commands. Here is a comparative analysis of these two methods:

Method Advantage Disadvantage
Dollar substitution
  • More readable and visually separates the command.
  • Supports easy nesting of commands.
  • May not be available in all UNIX system.
Backtick substitution
  • Widely supported in UNIX systems.
  • Less readable, may clutter the script.
  • Supports nesting but can become visually confusing.

I find dollar substitution to be straightforward and simple. On the other hand, nested backticks can be confusing and prone to errors. Therefore, if you don’t specifically require the use of backticks, dollar substitution would be a better choice.

3 Practical Cases of Setting Output of Command to Variables in Bash Script

There are various scenarios where it is useful or necessary to store the output of a command in a variable. In the following examples, I will discuss three common use cases where storing command output can be beneficial.

1. Disk Usage of Current Directory

To visualize the disk usage of the current directory, write the script below:


# Define the threshold for disk usage

# Get the disk usage for the current directory
disk_usage=$(df -h . | awk 'NR==2{print $5}')

# Extract the percentage value from the output
usage_percentage=$(echo "$disk_usage" | tr -d '%')

# Compare the disk usage against the threshold
if [ "$usage_percentage" -gt "$threshold" ]; then
echo "Disk usage for the current directory is above the threshold! Current usage: $disk_usage"
echo "Disk usage for the current directory is within the threshold. Current usage: $disk_usage"

This script checks the disk usage for the current directory by running the df -h. command. It extracts the disk usage percentage from the command’s output using awk and stores it in the disk_usage variable. The awk 'NR==2{print $5}' part prints the 5th field (disk usage percentage) from the second line of the df command output.

Then, the script removes the percentage sign from the disk_usage value using tr -d '%' and saves it as usage_percentage. It compares usage_percentage with a predefined threshold value (set to 80%).

If the disk usage exceeds the threshold, it prints a message stating that the disk usage is above the threshold. Otherwise, it prints a message indicating that the disk usage is within the threshold.

Finding disk usage using command outputThe image shows that 92% of disk space is used by the current directory which is above the preset threshold.

2. Ping Test of a Site Using Output of Commands

The ping command is the easy way to find the average ping test time. Now see a bash script to execute the ping test of a site using the output of commands:


# Prompt the user to enter the domain
read -p "Enter the domain to ping: " domain
ping_avg=$(ping -q -c 4 $domain | grep rtt)
echo "Avg ping time for $domain: $ping_avg"

The given script prompts the user to enter a domain name to ping. Once the user provides the input, the script uses the ping command to calculate the average ping time. The -q option ensures that only summary information is displayed. The output of the ping command is then passed through grep to extract the line containing the round-trip time (rtt). This filters out the average ping time and stores the output in the ping_avg variable using command substitution. Finally, the script displays the average ping time for the entered domain by echoing the values of the domain and ping_avg variables.

Average ping time of a siteHere, based on the given site domain the script finds the average ping time of the site

3. Create Files Based on the Output of Commands

One may need to perform certain tasks based on the output of commands in a Bash script. For example, one may want to create files based on the output of different other commands. Follow the script below to visualize this:

file="message.txt"  # Replace with the actual filename you want to read
# Check if the file exists in the current directory
if [ ! -f "$file" ]; then
echo "File '$file' does not exist in the current directory."
exit 1

# Count occurrences of the word "hidden" in the file
count=$(grep -o -i "hidden" "$file" | wc -l)
# Display the result
echo "Occurrences of 'hidden' in '$file': $count"

# Create new files for each hidden message
for ((i=1; i<=$count; i++)); do
touch "hidden_message${i}.txt"

# List the created files
echo "Created files for each hidden message:"
ls hidden_message*.txt

This script checks if a file named message.txt exists in the current directory. If the file does not exist, it displays an error message and exits. If the file exists, it counts the number of occurrences of the word “hidden” (case-insensitive) in the file using the grep command and saves the count in the variable count. Then, it creates new files named “hidden_message1.txt”, “hidden_message2.txt”, and so on, up to the count of occurrences. Finally, it lists the names of the created files using the ls command.

Creating files based on output of commandThe image shows that there is no message.txt file in the current directory. Let’s create one and put some text in it.Reading text using cat command in BashUsing the cat command one can print the text of message.txt. It seems the word “hidden” is 3 times in the text. Let’s see what happens after running the script.Creating files based on command outputSo this time the script finds the message.txt file and counts the word hidden in the text. After successfully counting that specific word it creates new files for each instance of the word “hidden”.

Error in Variable Usage That Stores Command Output

Sometimes prior familiarity with other programming languages may cause errors in variable assigning in Bash. Moreover one must have sufficient knowledge about command substitution to avoid such issues. You can go through the following two issues to have a better understanding.

A. Wrong Command Substitution

One may end up with a wrong command substitution because of a syntax error.


$(echo $(ls -l))

In a Bash script, command substitution does not operate in this manner. One can use echo outside of the dollar sign or, instead, store the output in a variable and then echo it.

echo $(ls -l)
output=$(ls -l)
echo $output

B. Incorrect Variable Assignment

Sometimes incorrect variable assignment causes errors in processing the variable later in the script. For example,

set $(hostname --short)=$(virsh --readonly list --state-running --name)

This is an example of a wrong variable assignment in Bash. The output of virsh command can’t be stored in the output of hostname command. Rather one can use variables to store output and later use those for further processing or printing. For example,

host=$(hostname --short)
state=$(virsh --readonly list --state-running --name)


In conclusion, there are mainly two ways of substituting commands in Bash. The dollar sign method is easy to comprehend. On the other hand, the backtick method can be long-winded and often cause errors. Hope you understand the techniques to set the output of a command to a variable in Bash.

People Also Ask

How to use a variable in command?

Just give a dollar($) sign before using a variable in a command. This will retrieve the value stored in the variable and can be used as parameters or arguments of a command.

Why Bash variable command is not found?

One may set a command or multiple commands in a variable. This is often known as an alias. One may set an alias wrongly and hence can not find it. This often occurs due to unnecessary whitespaces on both sides of equal sign.

How to redirect output of Bash command?

To redirect the output of Bash command to a file or to another command one can use the arrow sign(>).

How to write multiline shell command in Bash?

To write multiline shell command in Bash, you can use backslash \. Use backslash (\) at the end of a line to continue the command to the next line. Here’s an example:

echo "This is a/



This will give a single-line output: This is a multiline command.

How can I suppress output of a command in Linux?

To suppress the output of a command in Linux, you can redirect both standard output and standard error in the /dev/null file. This special file discards data. Here’s the syntax: command > /dev/null 2>&1. If you want to suppress only standard output, you can use this syntax: command > /dev/null.

Related Articles

<< Go Back to Bash Output | Bash I/O | Bash Scripting Tutorial

4.8/5 - (5 votes)
A Complete Guide for Beginners Enroll Course Now
icon linux
Md Zahidul Islam Laku

Hey, I'm Zahidul Islam Laku currently working as a Linux Content Developer Executive at SOFTEKO. I completed my graduation from Bangladesh University of Engineering and Technology (BUET). I write articles on a variety of tech topics including Linux. Learning and writing on Linux is nothing but fun as it gives me more power on my machine. What can be more efficient than interacting with the Operating System without Graphical User Interface! Read Full Bio

Leave a Comment