exit status $?

In shell (e.g. bash, sh, zsh), $? is a special variable that stores the exit status of the most recently executed command.

What $? means

• $? → exit code of the last command

• Exit codes are integers:

  • 0 → success
  • non-zero → failure (different numbers mean different errors)

Simple examples

1️⃣ Check if a command succeeded

ls /etc
echo $?

Output:

0

Meaning: ls /etc ran successfully.

2️⃣ Check if a command failed

ls /not-exist
echo $?

Output:

2

Meaning: ls failed (directory doesn’t exist).

Typical usage in scripts

Conditional check

some_command
if [ $? -ne 0 ]; then
    echo "Command failed"
    exit 1
fi

Shorter, idiomatic form (preferred)

some_command || {
    echo "Command failed"
    exit 1
}

Important details ⚠️

1. $? is overwritten immediately

   false
   echo "hello"
   echo $?
   

   This prints 0 (from echo), not from false.

2. Always read $? immediately after the command

   false
   echo $?   # correct
   

3. In pipelines:

   cmd1 | cmd2
   echo $?
   

   $? is the exit code of cmd2, not cmd1.

Quick mental model

$? answers: “Did the last command succeed?”

• 0 → yes
• non-zero → no