Bash Exit Codes

What is an Exit Code?

Every command returns a number when it finishes, called the exit code (or exit status).

• 0 means the command succeeded
• Any other number (1-255) means something went wrong

Read the Exit Code ($?)

The special variable $? holds the exit code of the last command:

ls names.txt
names.txt
echo $?
0

ls missing.txt
ls: cannot access 'missing.txt': No such file or directory
echo $?
2

$? changes after every command, so read it right away, or save it in a variable: status=$?.

Set the Exit Code (exit)

Use exit with a number to end a script and return that exit code:

#!/bin/bash
if [ ! -f config.txt ]; then
  echo "config.txt not found"
  exit 1
fi
echo "Config found"

./check.sh
config.txt not found

./check.sh
config.txt not found
echo $?
1

Run Only on Success (&&)

&& runs the next command only if the first one succeeded (exit code 0):

mkdir backup && cd backup && pwd
/home/user/backup

Run Only on Failure (||)

|| runs the next command only if the first one failed:

cat missing.txt 2> /dev/null || echo "File not found"
File not found

Use Exit Codes in if

An if statement can test a command directly. The if block runs when the command's exit code is 0:

#!/bin/bash
if grep -q "Emma" names.txt; then
  echo "Emma is on the list"
else
  echo "Emma is not on the list"
fi

./search.sh
Emma is on the list

The -q option makes grep quiet: it prints nothing and only sets the exit code.

Stop on the First Error (set -e)

By default, a script keeps running after a command fails. Add set -e at the top to stop the script as soon as a command fails:

#!/bin/bash
set -e
echo "Step 1"
ls missing.txt
echo "Step 2"

./strict.sh
Step 1
ls: cannot access 'missing.txt': No such file or directory

"Step 2" is never printed, because the script stopped when ls failed.

Common Exit Codes

• 0: Success
• 1: General error
• 2: Wrong use of a command (for example a bad option)
• 126: The command exists but cannot be run (no permission)
• 127: Command not found
• 130: The script was stopped with Ctrl+C