What command should I use to display the exit code of the previous command?

Tutorial on using exit codes from Linux or UNIX commands. Examples of how to get the exit code of a command, how to set the exit code and how to suppress exit codes.

Estimated reading time: 3 minutes

Table of contents

What is an exit code in the UNIX or Linux shell?

An exit code, or sometimes known as a return code, is the code returned to a parent process by an executable. On POSIX systems the standard exit code is 0 for success and any number from 1 to 255 for anything else.

Exit codes can be interpreted by machine scripts to adapt in the event of successes of failures. If exit codes are not set the exit code will be the exit code of the last run command.

How to get the exit code of a command

To get the exit code of a command type echo $? at the command prompt. In the following example a file is printed to the terminal using the cat command.

cat file.txt
hello world
echo $?
0

The command was successful. The file exists and there are no errors in reading the file or writing it to the terminal. The exit code is therefore 0.

In the following example the file does not exist.

cat doesnotexist.txt
cat: doesnotexist.txt: No such file or directory
echo $?
1

The exit code is 1 as the operation was not successful.

How to use exit codes in scripts

To use exit codes in scripts an

cat doesnotexist.txt
cat: doesnotexist.txt: No such file or directory
echo $?
1

#!/bin/bash

cat file.txt 

if [ $? -eq 0 ]
then
  echo "The script ran ok"
  exit 0
else
  echo "The script failed" >&2
  exit 1
fi

If the command was successful the exit code will be 0 and ‘The script ran ok’ will be printed to the terminal.

How to set an exit code

To set an exit code in a script use

cat doesnotexist.txt
cat: doesnotexist.txt: No such file or directory
echo $?
1

cat doesnotexist.txt
cat: doesnotexist.txt: No such file or directory
echo $?
1

#!/bin/bash

exit 1

Executing this script shows that the exit code is correctly set.

bash exit.sh
echo $?
1

What exit code should I use?

The Linux Documentation Project has a list of reserved codes that also offers advice on what code to use for specific scenarios. These are the standard error codes in Linux or UNIX.

• 1 - Catchall for general errors

• cat doesnotexist.txt
  cat: doesnotexist.txt: No such file or directory
  echo $?
  1
  

  9 - Misuse of shell builtins (according to Bash documentation)

• #!/bin/bash
  
  cat file.txt 
  
  if [ $? -eq 0 ]
  then
    echo "The script ran ok"
    exit 0
  else
    echo "The script failed" >&2
    exit 1
  fi
  

  0 - Command invoked cannot execute

• #!/bin/bash
  
  cat file.txt 
  
  if [ $? -eq 0 ]
  then
    echo "The script ran ok"
    exit 0
  else
    echo "The script failed" >&2
    exit 1
  fi
  

  1 - “command not found”

• #!/bin/bash
  
  cat file.txt 
  
  if [ $? -eq 0 ]
  then
    echo "The script ran ok"
    exit 0
  else
    echo "The script failed" >&2
    exit 1
  fi
  

  2 - Invalid argument to exit

• #!/bin/bash
  
  cat file.txt 
  
  if [ $? -eq 0 ]
  then
    echo "The script ran ok"
    exit 0
  else
    echo "The script failed" >&2
    exit 1
  fi
  

  3 - Fatal error signal “n”

• #!/bin/bash
  
  cat file.txt 
  
  if [ $? -eq 0 ]
  then
    echo "The script ran ok"
    exit 0
  else
    echo "The script failed" >&2
    exit 1
  fi
  

  4 - Script terminated by Control-C

• #!/bin/bash
  
  cat file.txt 
  
  if [ $? -eq 0 ]
  then
    echo "The script ran ok"
    exit 0
  else
    echo "The script failed" >&2
    exit 1
  fi
  

  5 - Exit status out of range

How to suppress exit statuses

Sometimes there may be a requirement to suppress an exit status. It may be that a command is being run within another script and that anything other than a 0 status is undesirable.

In the following example a file is printed to the terminal using cat. This file does not exist so will cause an exit status of 1.

To suppress the error message any output to standard error is sent to

#!/bin/bash

cat file.txt 

if [ $? -eq 0 ]
then
  echo "The script ran ok"
  exit 0
else
  echo "The script failed" >&2
  exit 1
fi

#!/bin/bash

cat file.txt 

if [ $? -eq 0 ]
then
  echo "The script ran ok"
  exit 0
else
  echo "The script failed" >&2
  exit 1
fi

If the cat command fails an

#!/bin/bash

exit 1

#!/bin/bash

exit 1

Combining both the suppression of error output and the

#!/bin/bash

exit 1

Which command is used to know the exit status?

How to check shell script exit code?

How to check the status of a previous command in Linux?

Is exit status of last command?