Need to create a shell script that would automatically backup and shutdown

Daggaroth · 11-29-2010, 10:53 AM

I would like to develop a shell script that would automatically run a backup program and then shutdown the computers, but I do not know the first thing about script development or even writing scripting. if anyone could help me out I would be greatly appreciated.

b0uncer · 11-29-2010, 11:14 AM

A script, at its shortest, is simply a series of commands that your shell understands (as if you typed them in yourself). To shut down your computer (from a terminal) you'd use something like shutdown,

Code:

man shutdown

A bash script, for example, could be simply

Code:

#!/bin/bash
shutdown

and after

Code:

chmod +x script.sh

you could run it (provided that the file was called script.sh and that shutdown was in a directory that was included in $PATH environment variable). You should probably put the whole path to shutdown into the script, to be sure. The first row in the script tells which interpreter should be used to run the script, in this case bash (there are lots of other options here, depending on how you want to do things, bash is just one way). Or, you could just put the word "shutdown" in the file (call it, say, "scriptfile") and run

Code:

sh scriptfile

and you'd very probably get the same result--here you'd explicitly make "sh" (which might actually be "bash") run the contents (or "script") of the given file. You wouldn't even have to make it executable using "chmod" if you did it this way. This way you can just add programs to be run into the script, like your backup program (whatever it is), and run the script. Or you could run it through cron for example, to make it all happen at some pre-specified time (just add the script to crontab, and make sure that you specify all executables with full path, to make sure everything works).

That's the basics. There are loads of tutorials out there about scripting on a variety of languages, so keep reading if you just got interested. After you get past the plain ol' running commands state, you'll soon learn you can do a bunch of things. Actually, your whole backup program can very well be "simply" a script, even though it did wonders. And yes, at some point you do want to know how to run your scripts at startup (init scripts) or at a given time (cron/anacron) or at shutdown or at the end of the day or at tea time or whenever you didn't know you wanted them to run..so get used to crons and such

The first problems you'll probably face when timing the running of your scripts, i.e. not running them yourself directly, are "program not found"s or equivalents, which are caused by you not telling exactly what to run and where from. As long as you work in your nice comfortable personal shell with a fancy environment defined, all works well, but you can't rely on all those environment variables etc. being set all the time (such as $HOME or $PATH -- try to echo them to see what they contain!).

Daggaroth · 12-03-2010, 01:26 AM

so if I wanted my script to do what I want it to do the entirety would be:

"
#!/bin/bash
chmod +x script.sh
run <insert backup program here>
if
command completed
Program < insert backup Program here> completed
then
Shutdown
sh scriptfile

"

would that work or am i missing something that would screw it up?

please keep in mind this is my very first time writing a script so I am not sure if it would work or not.

Disillusionist · 12-03-2010, 01:51 AM

No, there are a number of issues with your "script".

Firstly, what you have is pseudo code at the moment, which is fine as a starting point to structure your thoughts and decide what needs to be done, and in what order, I normally put in comments for this:

Code:

#!/bin/bash
###
### script to run a backup and then shutdown the computer
###
LOGFILE="/backup.log"
echo "Starting backup script $(date)" > $LOGFILE
###
### First I need to run the backup, but to where and using what program?
###
### There are multiple backup utilities including (but not limited to): tar, cpio, amanda, backup 
###
echo "Run backup script here..." >> $LOGFILE 2>&1

###
### Next I need to check the return code of the backup utility
###
if [ "$?" -eq "0" ]
then
   ###
   ### Utility worked - shutdown machine!
   ###
   echo "Shuting down the machine" >> $LOGFILE
else
   ###
   ### Utility failed! - ABORT
   ###
   echo "Backup FAILED! - Read the logfile $LOGFILE"
   exit 1
fi

Secondly, the chmod +x command in your post needs to be run on the script not from within the script.

Thirdly, there is no point in running a script post the shutdown command, as once this completes the script will have nothing to run against.

Hope this helps

Daggaroth · 12-03-2010, 02:08 AM

Ahhh! I see now,

thank you!

Daggaroth · 12-03-2010, 02:37 AM

Quote:

Originally Posted by Disillusionist

if [ "$?" -eq "0" ]

what does this specific aspect of the code do? Im not familiar with it. well specifically the aspect in the brackets

Disillusionist · 12-03-2010, 11:19 AM

When you run any command, the exit code is recorded in the special variable $?

An exit code of zero means that the previous command exited cleanly, normally meaning that the task worked.

It is important to note that this is the result of the previous command, so do not put any echo commands in between or this will ruin your test

The square brackets denote a test, so in pseudo code this would be:

Code:

##
## Test exit code of previous command.
##
## If this was zero the command worked :)
##
## Otherwise the command failed :(
##

In my section for a failure, I am using exit passing an exit code of 1, therefore you could perform a similar test on the script itself (although once this is configured to shutdown the machine on success this would seem a little self evident

)