[9fans] newbie rc question

[9fans] newbie rc question

[john]

So, after reading the Blit paper, I thought 'watch' looked pretty
neat and tried to make a simple rc script to act similarly. However,
when I use the script (at the end of this email) to try something
like this:
man -t ls > foo
watch foo | page

page says 'converting from troff to postscript' but then never
actually displays anything. I'm sure there's something basic
I'm forgetting here--can somebody help me figure out what's
wrong?

Here's the code (I apologize if it doesn't meet your standards)


#!/bin/rc
# Watch the specified file for changes; print out the file
# if there are any changes. 

if (~ $#* 1) {
	cat $1
	sum = `{sum $1}
	while () {
		newsum = `{sum $1}
		if (! ~ $sum(1) $newsum(1)) {
			sum = $newsum
			cat $1
		}
		sleep 1
	}
} 
if not {
	echo 'Usage: watch <file>'
}

Re: [9fans] newbie rc question

[erik quanstrom]

> page says 'converting from troff to postscript' but then never
> actually displays anything. I'm sure there's something basic
> I'm forgetting here--can somebody help me figure out what's
> wrong?

the file descriptor is never closed, thus page never stops to render
what it's got.

what you want is the same thing with the cmd rolled inside.  something
like

#!/bin/rc

if(! ~ $#* 2){
	echo usage: w file cmd >[1=2];
	exit usage
}

s=''
while(){
	n=`{sum $1| sed 's/ .*//g'}
	if(! ~ $s $n){
		s=$n
		$2 < $1
	}
	sleep 1
}

Re: [9fans] newbie rc question

[john]

>> page says 'converting from troff to postscript' but then never
>> actually displays anything. I'm sure there's something basic
>> I'm forgetting here--can somebody help me figure out what's
>> wrong?
> 
> the file descriptor is never closed, thus page never stops to render
> what it's got.
> 
> what you want is the same thing with the cmd rolled inside.  something
> like
> 
> #!/bin/rc
> 
> if(! ~ $#* 2){
> 	echo usage: w file cmd >[1=2];
> 	exit usage
> }
> 
> s=''
> while(){
> 	n=`{sum $1| sed 's/ .*//g'}
> 	if(! ~ $s $n){
> 		s=$n
> 		$2 < $1
> 	}
> 	sleep 1
> }

This doesn't quite allow for the same possibilities as the original
Unix program seemed to, where you could do:
watch fig1.pic | pic | troff | page
instead of being limited to just one command. Can the problem of
open file descriptors be solved in rc while still giving a nice general
tool, or is it necessary to go to C?


John

Re: [9fans] newbie rc question

[erik quanstrom]

> This doesn't quite allow for the same possibilities as the original
> Unix program seemed to, where you could do:
> watch fig1.pic | pic | troff | page
> instead of being limited to just one command. Can the problem of
> open file descriptors be solved in rc while still giving a nice general
> tool, or is it necessary to go to C?
> 
> 
> John

sure it does.  you could replace the $2 < $1 in the script with

	rc -c $2<$1

then your command would be

watch fig1.pic 'pic|troff|page'

- erik