What Does $? Mean in Bash? Mastering Exit Status and Conditional Commands

The variable $? is a special shell variable that holds the exit status of the most recently executed command; a value of 0 indicates success, while any non‑zero number signals an error.

In the shell, variables are referenced with a leading $, so the exit status is accessed as $?. For example:

# test -e /tmp/a.txt; echo $?
0   // file exists, exit status 0

If /tmp/a.txt does not exist, the same command returns a non‑zero status (typically 1).

Another illustration:

# echo 'onmpw'
onmpw
# echo $?
0
# 1name=onmpw
-bash: 1name=onmpw: command not found
# echo $?
127   // error code
# echo $?
0     // the previous command (echo $?) succeeded

The exit status is essential for controlling command flow. By using the logical operators && (AND) and || (OR), scripts can execute subsequent commands based on whether the preceding command succeeded.

Example with && and ||:

# test -e /tmp/a.txt && echo 'Yes' || echo 'No'
Yes   // file exists, first command succeeds, so echo 'Yes' runs

If the file does not exist:

# test -e /tmp/b.txt && echo "Yes" || echo "No"
No    // first command fails, so the OR part runs

In these expressions, && proceeds to the right‑hand command only when the left‑hand command returns 0, while || proceeds when the left‑hand command returns a non‑zero status. Understanding $? together with these operators enables reliable conditional execution in shell scripts.