Testing server setup bash scripts - bash

Question

I'm just learning to write bash scripts.
I'm writing a script to setup a new server.
How should I go about testing the script.
i.e.
I use apt install for certain packages like apache, php etc. and then a couple of lines down there is an error.
I then need to fix the error and run it again but it will run all the install commands again.
The system will probably say the package is installed already, but what if there are commands which append strings to files.
If these are run again it will append the same string to the file a second time.
What is the best approach to write bash-scripts like this?
Can you do test runs which rollback everything after an error or end of the script?
Or even better to have the script continue from the line where the error occured the next time it is run?
I'm doing this on an Ubuntu 18.04 server.

Answer 1

it's a matter of how clear you want it to be to read it, but
[ -f .step01-done ] || your install command && touch .step01-done
[ -f .step02-done ] || your other install command && touch .step02-done
maybe a little easier to read:
if ! [ -f .step01-done ]; then
if your install command ; then
touch .step01-done
fi
fi
if ! [ -f .step02-done ]; then
if your other install command ; then
touch .step02-done
fi
fi
...or something in between.
Now, I would suggest creating a directory somewhere and maybe logging output from the commands to some file there (maybe tee it) but definitely putting all these files you are creating with touch there. That way if you start it from another directory by accident, it won't matter. You just need to make sure that apt-get or whatever you use actual returns false if it fails. It should.
You could even make a function that does it in a nice way...
#!/bin/bash
function do_cmd() {
if [ -f "$1.done" ]; then
echo "$2: skipping already completed step"
return 0
fi
echo -n "$2: "
$3 1> "$1.out" 2> "$1.err"
if $?; then
echo "ok"
touch "$1.done"
return 0
else
echo "failed"
echo -e "see \"$1.out\" and/or \"$1.err\" for details."
return 1
# could "exit 1" instead
fi
}
[ -d /root/mysetup ] || mkdir /root/mysetup
if ! [ -d /root/mysetup ]; then
echo "failed to find or create /root/mysetup directory
exit 1
fi
cd /root/mysetup
# ---------------- your steps go here -------------------
do_cmd prog1 "installing prog1" "apt-get install prog1" || exit 1
do_cmd prog2 "installing prog2" "apt-get install prog2" || exit 1
do_cmd startfoo "starting foo service" "service foo start" || exit 1
echo "all setup functions finished."
You would use:
do_cmd identifier "description" "command or function"
description
identifier: unique identifier used when files are generated:
identifier.out: standard output from command
identifier.err: standard error from command
identifier.done: created when command is successful
description: this is actually printed to the terminal when the step is being executed.
command or function: this is the actual command to run
not sure why stackoverflow forced me to format that last bit as code but w/e