[uae] Re: Very ugly hdfcreator in bash
- From: elmar@xxxxxxxxxxxxxxxxxx
- To: uae@xxxxxxxxxxxxx
- Date: Thu, 30 Jun 2005 11:28:33 +0200
Hi Gingat!
> Gingat Florent wrote:
[snip]
> Elmar can you explain me a little this =
>
> count=*`**echo* $2 "2048 * p q" *|* *dc* -*`
>
> I mean i've understand the echo $2 (2 come from the second input) but "2048
> * p q"
>
> I d'ont understand it's a multiplication but what * what :p ?
Sorry, maybe "quoted-printable" was the wrong choice for the attachment.
I'll paste the script at the bottom of this mail.
Calculations in the shell are a bit tricky. The least common denominator seems
to be the 'dc' command (desktop calculator?) which features some reverse polish
notations (like in forth or postscript ...).
Unfortunately dc expects a file which contains the appropriate commands. Now,
the special file name '-' means standard input. So the following commands get
piped into dc via the echo command
(in human readable form)
Push $2 (the second argument of the script) onto the stack
Push 2048 onto the stack
Multiply (*) the two top-most values on the stack (leaving its result on the
stack)
Print the top-most value on the stack (p)
Quit (q)
The reverse ticks `...` allow us to save the output of this command
(the number printed) in $count.
Browsing through the bash manual I just found the chapter "Arithmetic
expressions".
The command
let count=2048*$2
also seems to do the job. But then the script wouldn't be ugly any more :)
(and it would only work with a bash).
Regards,
Elmar.
---------------------------------------
#!/bin/bash
echo; echo "HDFCreator v0.01 fgingat__at_____gmail__dot__com, v0.1 e. plischke"
if [ $# -ne 2 ]; then
echo $0 " needs arguments name and size (in MB)"
exit 1
fi
if [ -e $1 ]; then
echo File $1 exists.
exit 1
fi
count=`echo $2 "2048 * p q" | dc -`
dd if=/dev/zero of=$1 bs=512 count=$count
exit 0
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