Meaning of $? (dollar question mark) in shell scripts

198

What does

echo $?

mean in shell programming?

This question is tagged with shell scripting special-characters

~ Asked on 2011-08-30 18:33:47

The Best Answer is


232

This is the exit status of the last executed command.

For example the command true always returns a status of 0 and false always returns a status of 1:

true
echo $? # echoes 0
false
echo $? # echoes 1

From the manual: (acessible by calling man bash in your shell)

$?       Expands to the exit status of the most recently executed foreground pipeline.

By convention an exit status of 0 means success, and non-zero return status means failure. Learn more about exit statuses on wikipedia.

There are other special variables like this, as you can see on this online manual: https://www.gnu.org/s/bash/manual/bash.html#Special-Parameters

~ Answered on 2011-08-30 18:35:39


22

$? returns the exit value of the last executed command. echo $? prints that value on console. zero implies a successful execution while non-zero values are mapped to various reason for failure.

Hence when scripting; I tend to use the following syntax

if [ $? -eq 0 ]; then
 # do something
else
 # do something else
fi

The comparison is to be done on equals to 0 or not equals 0.

** Update Based on the comment: Ideally, you should not use the above code block for comparison, refer to @tripleee comments and explanation.

~ Answered on 2014-12-16 09:21:31


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