How can I use exit codes to run shell scripts sequentially?

Question

Since cruise control is full of bugs that have wasted my entire week, I have decided the existing shell scripts I have are simpler and thus better.

Here is what I have so far

svn update /var/www/k12/
#svn log --revision "HEAD" /var/www/code/  | head -2 | tail -1 | awk '{print $1}' > /var/www/path/version.txt

# upload the files
rsync -ar --verbose --stats --progress --delete --exclude=*.svn /var/www/code/ example.com:/home/path

# bring database up to date
ssh example.com 'php /path/tasks/dbrefactor.php'

# notify me
ssh example.com 'php /path/tasks/build.php'

Only thing is the other day I changed the paths and forgot to update the rsync call. As a result the "notify me" step ran several times while I was figuring stuff out.

I know in linux you can do command1 && command2 and if command 1 "fails" command2 will not run, but how can I observe the "failure/success" exit codes for debugging purposes. Some of the scripts I wrote myself and I'm sure I will need to do something special.

Answer 1

The return value of the last-run command is stored in the variable $?. You can use that to determine which command to run next. Overview of special variables.

Answer 2

i think $? contains the last exit code

if [[ -z $? ]]
then
  # notify me
  ssh example.com 'php /path/tasks/build.php'
fi

Answer 3

The exit code of a previous process happens to be in $? variable right after its execution. Usually (that's not required, but it's the convention everyone follows) the exit code of a successful command will be equal to 0, and any other value means an error.

Remember of the caveats! One of them is that after these commands:

svn log --revision "HEAD" /var/www/code/  | head -2 | tail -1 | awk '{print $1}'
echo "$?"

the zero result would most likely be returned, because in the $? the return code of awk is contained. To avoid it, set the pipefail option somewhere above the code:

set -o pipefail 1

Answer 4

I would suggest you can use the exit non zero at the points where the failure is expected and before processing step further you will check if [ $? -neq 0 ] then there is a failure.

---

The $? will always return a non zero number if the last process does not executed successfully.