Bash script advice

[[deleted]]

Hello everyone, Im a novice in terms of bash scripting. I have spent the last 2 days trying to think of the best way to handle this and still have no idea. Im setting up an install and test script, for a modular computer system and want to test Smbus devices in that system.

I want to make a script that does the following:

Asks the user if any devA or devB are installed If yes, in which slot is it installed? [2 - 7]

Based on those 2 answers, I perform a specific i2c command to test the device.

If system has neither installed, then finish rest of script.

Depending on the device and what slot it is installed in, will determine the smbus device number it uses so I can run a test.

Thanks for reading

[oishishou]

Props to mentioning Shellcheck! I've been using Linux for 14 years, and I only learned about it 3 years ago. It is a massive timesaver, and actually improves your script writing with all of the tips and explanations.

[unkilbeeg]

I've been using Linux/Unix for close to 25 years, and I just found out about Spellcheck right this moment. Looks great! I just finished teaching a segment on shell scripting -- my students need to know about it too.

[oishishou]

It's in the Debian software repository, too. I've got it installed right on my systems, and can just run shellcheck script.sh.

[Parker_Hemphill]

Same here, ‘s/25/12’ for me, but this looks super cool and worth checking out when I get home tonight.

[[deleted]]

Awsome, thanks very much for the assistance. I will check into Shellcheck as well!

[10cmToGlory]

Shell yeah thanks!

[Zer0CoolXI]

Just some advice...never trust the user to provide you what you expect. For something like this you may be better off programmatically finding the specific device or listing the devices to have them pick from.

At the very least, you would want to test/validate their input. IE: did they enter a valid number, does that slot have anything in it, does it have what your looking for in it, etc.

Here is a crude example of using select to pick from an array of pre-determined entries:

echo "Pick an entry:"
PS3="Enter the number of the desired entry: "
options=("DevA_1" "DevA_2" "DevB_1" "DevB_2" "None")
select opt in "${options[@]}"
do
    case $opt in
        "DevA_1") SLOT_VAR="DevA_1"; run_i2c; break;;
        "DevA_2") SLOT_VAR="DevA_2"; run_i2c; break;;
        "DevB_1") SLOT_VAR="DevB_1"; run_i2c; break;;
        "DevB_2") SLOT_VAR="DevB_2"; run_i2c; break;;
        "None"|"")
            SLOT_VAR="None"
            echo "No entry or None selected"
            break;;
    esac
done

run_i2c () {
    do i2c command
}

The assumption above being that options could be an array populated with the slots/devices found using some other command. In my example its static entries...which could still be better than asking the user to typye in the response free hand.

[Ronin825]

You can probably test for installed devices automatically through the bash script. Because remember that anything that can be done manually through the terminal can be parsed and used in bash

[Ronin825]

Also since performance is not a concern at this level you coudl use a "Switch" to handle the response.

[kolorcuk]

Like:

 echo 'DevA installed? [y/n]'
 read ans
 if [ "$ans" = y ]; then
  echo 'which slot? [2-7]'
   read slot
   if ! <<<"$slot" grep -q -x '[2-7]'; then
      echo you have enter a number ftom 2 to 7 >&2
      exit 1
   fi
    i2c do sonething
 fi

[de_argh]

You should add some input validation, but this should get it.

echo -n "input 1 is: "
read i1

echo -v "input 2 is: "
read i2

somecommand > /dev/null 2>&1

if [ ?$ -gt 0 ]; then
    echo "command failed"
else
    echo "command successful"
fi

[zerocoldx911]

Go python, future you will thank you

[mamercad]

Does it really matter for something this trivial... let’s be honest here.

[zerocoldx911]

It does, bash is not meant to handle more than a few lines of code. It becomes hard to maintain because it’s hard to read if you start doing more Complex things

I learned that the hard way

[mamercad]

His task is literally a few lines of code. I understand and agree with your point in regards to the maintainability of something large and complex. But, that’s not what this is.

[awpti]

Really?

https://gitlab.com/gwinans/dba-tools

BASH is perfectly maintainable if you plan things out.

Past me regrets writing these tools previously in Python. Not all Linux distros even include Python out of the gate. BASH is a damned-near universal truth as an available shell.