Explain Different EXIT Commands in UNIX

Question

I understand that EXIT command causes the shell or program to terminate. But what is the difference between the below:

exit 2
exit 3
exit 4
exit $?

how is exit 2 different from exit 3 and so on

@tripleee: not really a duplicate, the OP is asking about `exit` not about possibly standard meanings of return code values. — isedev, Feb 18 '14 at 17:10

score 3 · Answer 1 · answered Feb 18 '14 at 16:43

3

This is only an exit code. 0 is for fine exit, otherwise it's the error code. $? is a shell variable storing the previous exit value (so the program which ran before your one).

answered Feb 18 '14 at 16:43

bagage

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More precisely, it's a shell variable or shell parameter. It's not an environment variable. – Barmar Feb 18 '14 at 16:45
`bash` distinguishes shell variables as a parameter denoted by a name. This excludes the positional parameters (denoted by non-zero numbers) and the special parameters (denoted by various punctuation marks, symbols and 0). – chepner Feb 18 '14 at 17:36

score 2 · Answer 2 · answered Feb 18 '14 at 16:47

The exit command takes a single value which is the value of the process (e.g. shell) return code. $? is the return code from the last command executed by the shell.

For instance, the script which exits with a return code corresponding to the first argument:

#!/bin/sh
exit $1

Would give you:

# ./script 1
# echo $?
1
# ./script 2
# echo $?
2

Note on most UNIX systems, the return code is limited to a numeric value between 0 and 255, with 0 indicates success and 1-255 providing error information (specific to each process).

Oh I got it thanks alot for the intel – Rahul sawant Feb 18 '14 at 16:51 — Rahul sawant, Feb 18 '14 at 16:51

score 1 · Answer 3 · edited May 23 '17 at 11:49

From the Advanced Bash-Scripting Guide, Chapter 6: Exit and Exit Status:

The exit command terminates a script, just as in a C program. It can also return a value, which is available to the script's parent process.

So the exit command lets you assign your own exit value, which you could describe in its man page, for example.

The $? will return the exit code of the previous command. For example; You write a script that executes cat example.txt, which results exit code 1. If you then do exit $?, your script will exit with the same code as cat example.txt

More info on exit codes here: Advanced Bash-Scripting Guide Chapter 6: Exit and Exit Status
Some info on $? here: What is the $? variable in shell scripting?

Explain Different EXIT Commands in UNIX

3 Answers3