Learning how to bash script, questions.

Cows · 2012-01-13 21:53:39

Hello everyone,

So I'm learning how to Bash script so I can improve my AUR packages, and also make some scripts for my personal use.

I've been working on a basic script that completely cleans your kernel source tree while saving your config file.

I was wondering if this is good and up to today's standards (Meaning checking existence of files, and checking return status for previous command):

#!/bin/bash

mv .config config 

if [ -e "config" ] ; then
    echo "Configuration has been backed up successfully."
else
    echo "Error renaming, quitting program."
    exit
fi

echo "Cleaning your kernel source tree!"

make distclean

if [ $? -eq 0 ]; then
    echo "Your kernel source tree was clean successfully."
else
    echo "Error cleaning your kernel source."
fi

mv config .config

if [ -e ".config" ] ; then
    echo "Configuration has been installed successfully."
else
    echo "Error renaming, quitting program."
    exit
fi

/dev/zero · 2012-01-13 22:59:45

What happens if you accidentally run it in your home directory? You probably don't want to be moving your .config folder around like this, even if it doesn't get hurt. Also, what happens if there's a pre-existing "config" file or folder? You should probably inform the user to deal with it, and bail out.

I would also consider using more verbosity, eg in the calls to "mv", and make the echo statements more descriptive and maybe use some colour.

In summary, if it were me, a first draft before playing with it more might look a bit like this:

#!/bin/bash
set -e

RED="\[\033[31m\]"
GREEN="\[033[32m\]"
BLUE="\[033[34m\]"
RESET_COLOURS="\[\033[0m\]"

CONFIG_FILE=".config"
BACKUP_FILE="config"

if [[ -f "$CONFIG_FILE" && ! -f "$BACKUP_FILE" ]]; then
    printf "Backing up existing configuration: $BLUE"
    mv -v "$CONFIG_FILE" "$BACKUP_FILE"
    printf "${RESET_COLOURS}\n"
else
    echo "Existing configuration not found or backup already exists, nothing to do."
    exit
fi

printf "Cleaning kernel source tree in $(pwd) ... "
make distclean
if [ $? -eq 0 ]; then
    printf "${GREEN}Success!${RESET_COLOURS}\n"
else
    printf "${RED}Failed!${RESET_COLOURS}\n"
fi

if [[ -f "$BACKUP_FILE" && ! -f "$CONFIG_FILE" ]] ; then
    printf "Restoring pre-existing configuration: $BLUE"
    mv -v "$BACKUP_FILE" "$CONFIG_FILE"
    printf "${RESET_COLOURS}\n"
else
    echo "Backed up configuration not found or pre-existing configuration already there, nothing to do."
    exit
fi

Last edited by /dev/zero (2012-01-13 23:03:10)

Cows · 2012-01-14 04:14:16

Thanks for the help, but remember though that this is a personal script and it's not mean't to be redistributed. So I know exactly when and where I'm running it. That's why I didn't include some checks, even though as time goes on I probably would end up adding them anyways.

/dev/zero · 2012-01-14 04:18:57

Cows wrote:

Thanks for the help, but remember though that this is a personal script and it's not mean't to be redistributed. So I know exactly when and where I'm running it. That's why I didn't include some checks, even though as time goes on I probably would end up adding them anyways.

Well, I wasn't telling you how to do it. Do it how you want.

I've just made enough mistakes over the years that I know I should treat myself as just another stupid user who needs checks in place. I'm constantly switching between different terminals which each have ssh sessions open to different computers at different times, so it's easy to lose track.

All you have to do is run the script when you're a bit tired and you'll see why it might make sense to be a bit more cautious.

Edit: I was going to say something about you being ungracious, but okay, you did say thank you.

Last edited by /dev/zero (2012-01-14 04:22:26)

Cows · 2012-01-14 04:52:07

I wasn't trying to offend you, and I also did say that since I'm still learning, I just wrote what I could to get the job done, without any checks as well. Eventually though when I become better at bash scripting, I will add more checks and take your advice into consideration. I also love the color codes .

Last edited by Cows (2012-01-14 04:52:24)

fukawi2 · 2012-01-14 07:47:49

Another way to handle this this, with error handling is like this

#!/bin/bash

echo "Making backup of config"
mv .config config || { echo "Error renaming, quitting program."; exit 1; }

You can do the same with all the other testing you do.

Also, don't forget that a non-zero exit status indicates failure (by convention) so if you are exiting because of an error, you should do so with non-zero.

cfr · 2012-01-20 02:30:12

mv -n

Arch Linux

#1 2012-01-13 21:53:39

Learning how to bash script, questions.

#2 2012-01-13 22:59:45

Re: Learning how to bash script, questions.

#3 2012-01-14 04:14:16

Re: Learning how to bash script, questions.

#4 2012-01-14 04:18:57

Re: Learning how to bash script, questions.

#5 2012-01-14 04:52:07

Re: Learning how to bash script, questions.

#6 2012-01-14 07:47:49

Re: Learning how to bash script, questions.

#7 2012-01-20 02:30:12

Re: Learning how to bash script, questions.

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