Shell Scripting Questions, Writing alarm clock script
 

I left the linux world for a few years and now i am trying to re-learn my shell scripting basics. I am writing a script for an alarm clock, but i seem to be running into a few issues. My script is posted below. If anyone could help, that would be great. Thanks.

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#!/bin/bash
declare -i H
declare -i M
declare -i currentH
declare -i currentM
declare -i minutesLeft
declare -i hoursLeft
echo -e "What Hour (24 Format) do you want to Wake Up?"
read H
echo -e "What Minute?"
read M
echo `expr $H + 0`
currentH=`date +%H`
currentM=`date +%M`
echo "You Selected "
echo "$H:$M"
echo -e "\nIt is Currently $currentH:$currentM"

if [ "$currentH" < "echo $H" ];
then
hoursLeft= `expr $H - $currentH`
echo "$H - $currentH means You Have: $hoursLeft hours still"
fi

if [ "$currentH" > "$H" ]; then
hoursLeft= `expr $currentH - $H`
echo -e "\n$currentH - $H means you have $hoursLeft hours left \n"
fi

if [ "$currentH" == "$H" ]; then
hoursLeft= 0
echo -e "Taking a nap?\n"
fi

if [ "$currentM" < "$M" ];
then
minutesLeft= `expr $M - $currentM`
echo -e "$M -$currentM menas you have: $minutesLeft minutes still"
fi




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My script, instead of doing what it should, produces the following errors:

./alarm: line 19: echo 11: No such file or directory
./alarm: line 26: 6: command not found

17 - 11 means you have hours left

./alarm: line 37: -41: command not found
11 -52 menas you have: minutes still
expr: non-integer argument
52 - 11 means you have 0 minutes left

Sleeping... for hours and 0 minutes

sleep: invalid time interval `h'
Try `sleep --help' for more information.

and if i choose the time 11:06, files called 11 and 6 are creating in the working directory. I am sure it is something really simple, but i haven't used linux or scripting on my computers in around 6 years. Thanks.

What are you trying to do here?

If you're comparing whether the current hour value is less than the alarm hour, then the "echo " makes no sense.

Could you repost your code at http://pastebin.com/ (select Bash) so we can have line numbers, monospacing, and syntax highlighting?

Yes the echo does not make sense. Sorry about that. That actually should have been cleaned up, but I deleted it from my script, but forgot to delete it from here.

Thanks for the quick response.

Here's a few tips to get you further along:

1) When comparing integers, do it like this:
Notice no quotations around the variable and the 3. When you use quotations, it should be for strings. -gt means "greater than", but there are other for less-than, equals, etc.. See bash man page for more on this.

2) When assigning values to vaiables, make sure there's no space after the "=" sign:

3) What does this do:
I mean, I know it supposed to echo something, but why? Just curious.... And for what it's worth, a bit less clunky way of doing simple math is like this, without expr:
Anyhow, check out that stuff and fix up your code a little. Then re-post the updated version for us in your next post. Please use code tags around your script ( see here: http://www.phpbb.com/community/faq.php?mode=bbcode#f2r1 )

Cheers.

I am trying to set an alarm. I am going to add a command to invoke mplayer at the given time after the sleep commands, but this is more than anything just me trying to get back into scripting. Kind of frustrating, because I used to be able to do kind of task fairly easily. Somehow I completely forgot almost everything.

Posted to
http://pastebin.com/TMH7qtXk

Thanks

Thanks AlucardZero and GrapefruiTgirl. Fixed it now. Runs well now. Here is the new code:

Thanks everyone. Responses were quick and helpful.

Is it necessary for me to declare the variables as integers?

Not really, no. There must be a good reason that `declare` exists, (and actually I saw a recent example where it HAD to be used to define an array before using it) but I virtually never declare integers in any scripts I write. Doesn't seem to matter. The bash man page says:
So that's good for me. Someone else may have other thoughts on this...

However! I should add that, something to keep in mind is that: if you're doing integer comparisons with variables, and one or another variable that has not been given a value (or zero), but you expect it to have an integer (not a string) then you can get errors. Like so:
I had not set the variable $c to anything at all, so the error results. If I had set an integer value to $c there would be no error. Using `declare` beforehand, does not prevent this.

So i should set my integer variables equal to a non-zero number first? Thanks. The last code i posted doesn't work under all circumstances, but now that I have the very basics worked out, it shouldn't be too difficult. Thanks so much.

Well, take for example the following simple script:
Logically, there's nothing wrong with the script. However, you see there's the possibility that the $c variable will not get set to 5 (or any other integer) and so in this case, if you run the script, it will fail with an error (unless you set NAME="fred" in the beginning).

To prevent the error, make sure $c will ALWAYS contain some integer, including zero, before comparing it. Tthere should either be an ELSE case to go with the IF test of the name, which sets c to some value other than 5; or, you should initialise c=0 at beginning of the script. So:
Above, I added an ELSE, which sets $c to an integer; Now, $c ends up being an integer, regardless of what the $NAME was. No error is possible now, and we do not need to initialize c=0 in the start of the script.

Finished Script.
 

Okay Thanks for all your help. After reading your replies I started over from scratch, and it works well now with no errors. Also, I added a countdown timer as well. Here is my new code. Try it out, and tell me what you think.