Bash: Assign Output of Shell Command To Variable

How do I assign the output of a shell command to a shell variable under Unix like operating system? For example, I want to store the date command output to a variable called $now. How do you do that?

You need to use command substitution feature of bash. It allows you to run a shell command and store its output to a variable. To assign output of any shell command to variable in bash, use the following command substitution syntax:

 
var=$(command-name-here)
var=$(command-name-here arg1)
var=$(/path/to/command)
var=$(/path/to/command arg1 arg2)
 

OR

 
var=`command-name-here`
var=`command-name-here arg1`
var=`/path/to/command`
var=`/path/to/command arg1 arg2`
 

Do not put any no spaces after the equals sign and command must be on right side of =. See how to assign values to shell variables for more information.

Example

To store date command output to a variable called now, enter:

 
now=$(date)
 

OR

 
now=`date`
 

To display back result (or output stored in a variable called $now) use the echo or printf command:

echo "$now"

OR

printf "%s\n" "$now"

Sample outputs:

Wed Apr 25 00:55:45 IST 2012

You can combine the echo command and shell variables as follows:

echo "Today is $now"

Sample outputs:

Today is Wed Apr 25 00:55:45 IST 2012

You can do command substitution in an echo command itself (no need to use shell variable):

echo "Today is $(date)"

OR

printf "Today is %s\n" "$(date)"

Sample outputs:

Today is Wed Apr 25 00:57:58 IST 2011

See also:

• Command substitution - from the Linux shell scripting tutorial wiki.

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