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Kostas Pelelis
Kostas Pelelis

Reputation: 1342

Bash $? Variable Assignement

I just started learning bash and I was reading about the $? variable. From what I understood, $? is assigned to the exit status of the last command executed.

For example

$ false; echo $?

Will yield 1, and

$ false; :; echo $?

Will yield 0

Things get a bit more complicated when I combine these with if/for blocks. The man page reads:

for NAME [in WORDS ... ] ; do COMMANDS; done

Execute commands for each member in a list.

The for loop executes a sequence of commands for each member in a list of items. If in WORDS ...; is not present, then in "$@" is assumed. For each element in WORDS, NAME is set to that element, and the COMMANDS are executed.

Exit Status:

Returns the status of the last command executed.

That means:

$ false; for i in 1 2 3; do false; done; echo $?

Will yield 1 since the last command executed is false. But

$ false; for i in; do false; done; echo $?

or

$ false; if false; then :; fi; echo $?

Will yield 0 despite the fact that false was the last command executed.

My guess is the $? variable is set to 0 when entering a for/if block. Am I missing something?

Upvotes: 3

Views: 108

Answers (3)

pynexj
pynexj

Reputation: 20728

According to bash's manual:

if list ; then list ; [ elif list ; then list ; ] ... [ else list ; ] fi

The iflist is executed. If its exit status is zero, the thenlist is executed. Otherwise, each eliflist is executed in turn, and if its exit status is zero, the corresponding thenlist is executed and the command completes. Otherwise, the elselist is executed, if present. The exit status (of the whole if ... fi block) is the exit status of the last command (in the then, elif or else block) executed, or zero if no condition tested true.

Upvotes: 4

Nahuel Fouilleul
Nahuel Fouilleul

Reputation: 19315

yes, after if ..;, for ..; or while ..; statements the exit status reset to 0.

to be clear this doesn't mean after fi; or done; because the exit status is the last command exit status.

EDIT : commands between if/elif and then doesn't affect exit status of compound statement whereas latest command executed between then/else and elif/fi sets the exit status of compound statement.

after a function call; the exit status will be the value returned by return or the exit status of last command.

with the option set -e, set -o errexit; the shell exits after a command with a <>0 exit status, except if followed by || or inside a if ..; statement.

exit status must be checked just after command exits, logical operators can be used &&, ||:

# to fail fast the process can't continue
simple_command || {
    echo "failed .."
    exit 1
}

the error handling is similar to exceptions, the question to be asked is does or how the process can continue after a command fails?

in pipeline commands the exit status is the exit status of the last command except with set -o pipefail : the exit status will be the exit status of the latest command in the pipe with exit status <>0.

Upvotes: 3

Addison
Addison

Reputation: 121

Command $ false; for i in; do false; done; echo $? gives the exit status of for loop. Since it exits for-loop without errors, $? is 0. Here is a similar question which may be helpful. How to get the exit status a loop in bash

Upvotes: 1

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