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How To Access the Last Return Value in Bash

Ubuntu 18

Bash, or the Bourne Again Shell, is a popular command-line interpreter used in many Linux distributions. It’s a powerful tool that allows users to interact with the system, run commands, and even write scripts to automate tasks. One of the features of Bash is the ability to access the last return value of a command. This article will guide you on how to do that.

Quick Answer

To access the last return value in Bash, you can use the special variable $?. It automatically holds the exit status of the last executed command.

Understanding Return Values in Bash

Before we delve into how to access the last return value in Bash, it’s essential to understand what a return value is. Whenever you execute a command in Bash, it returns an exit status (or return value) to indicate whether it was successful or not. This exit status is an integer number where 0 indicates success and any non-zero value (1-255) indicates an error.

Accessing the Last Return Value

Bash provides a special variable, $?, to access the exit status of the last command. This variable is automatically set by the system and contains the return value of the last executed command.

Here’s an example:

echo "Hello, World!"
echo $?

In the above example, the echo command prints “Hello, World!” and returns an exit status of 0 (since the command was successful). The second echo command then prints this exit status.

Using the Return Value

The $? variable is particularly useful when you want to check if the previous command was successful or not. For example, you might want to stop the execution of a script if a certain command fails. Here’s how you can do it:

command_that_might_fail
if [ $? -ne 0 ]; then
 echo "The command failed. Aborting."
 exit 1
fi

In this example, if command_that_might_fail fails (i.e., its exit status is not 0), the script prints an error message and exits.

Accessing Command Output

It’s important to note that the $? variable only holds the exit status, not the output of the command. If you want to store the output of a command, you can use command substitution:

output=$(find -name '*.wsdl')

In this example, the find command’s output is stored in the output variable. To access this output, you can simply use $output.

Conclusion

In Bash, accessing the last return value or the output of a command is straightforward. By using the $? variable and command substitution, you can write more robust scripts and better handle errors. Remember that practice is key when it comes to mastering these concepts, so don’t hesitate to experiment with different commands and scripts. Happy scripting!

For more information on Bash scripting, you can visit the GNU Bash manual.

How can I check if the last command was successful or not?

To check if the last command was successful or not, you can use the $? variable. If the value of $? is 0, it means the last command was successful. If it is any other non-zero value, it means the command failed.

How can I use the last return value in an if statement?

You can use the last return value in an if statement by referencing the $? variable. For example, you can use the following syntax:

if [ $? -eq 0 ]; then
 # Code to execute if the last command was successful
else
 # Code to execute if the last command failed
fi
Can I access the output of the last command using the `$?` variable?

No, the $? variable only holds the exit status of the last command, not its output. If you want to access the output of a command, you need to use command substitution or redirect the output to a file or variable.

How can I store the output of a command in a variable?

You can store the output of a command in a variable using command substitution. The syntax is as follows:

variable=$(command)

For example, to store the output of the date command in a variable called current_date, you can use:

current_date=$(date)

You can then access the value of current_date using $current_date.

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