Plan 9: An rc approximation of rsc's https://pkg.go.dev/9fans.net/go/acme/Watch

Watch

#!/bin/rc
# An rc approximation of rsc's https://pkg.go.dev/9fans.net/go/acme/Watch
#
# Usage: Watch [-r | -n] [-d DIR] [CMD]
#   -s	starts command immediately
#   -r		listen for Put on subdirs recursively.
#   -n	only run the commands when Get is run
#   -d	cd to given dir, and listen for Put on files under it
# Flags taking no param may be combined eg: -sr
#
# You can add any number of commands in the +Watch window, prefixed
# with '% '.
# The +Watch window is marked as dirty while the commands are running.
# If a command fails, the subsequent commands are not run.
#
# Bugs:
# - If Kill is used, the commands not yet run are forgotten.
# - Tabs in command lines are replaced with spaces.
# - No attempt is made to quote params with spaces, semicolon, etc.

rfork en

fn log{
	#echo $* >[1=2]
}

name='+Watch'
dumpcmd='Watch '^$"*
dir=`{pwd}

start=n
recursive=n
nowatch=n
while(~ $1 -*){
	log flag: $1
	if(~ $1 *s*) start=y
	if(~ $1 *r*) {
		recursive=y
		name='+Watch-r'
	}
	if(~ $1 *n*){
		nowatch=y
		name='+Watch-n'
	}
	if(~ $1 -d){
		dir=$2
		shift
	}
	shift
}

cd $dir
~ $dir */ || dir=$dir/
rx=$dir ^ '[^/]+$'
if(~ $nowatch y)
	rx=nevermatch
if not
	if(~ $recursive y) rx=$dir
log rx: $rx

args=$"*
win=`{cat /mnt/acme/new/ctl | awk '{print $1}'}
w=/mnt/acme/$win
cmdpidfile=/tmp/Watch.cmdpid.$pid

fn ctl{ echo $* >$w/ctl }
fn tag{ echo -n $* >$w/tag }
fn body{ echo -n $* >$w/body }
fn data{ echo $* >$w/data }
fn addr{ echo -n $* >$w/addr }

log 'win:' $win
ctl 'name ' ^ $dir ^ $name
ctl dumpdir $dir
ctl dump $dumpcmd
ctl cleartag
tag ' Look Get Kill'
body '% ' ^ $"args
ctl clean

fn sigint{
	log sigint
	if(test -f $cmdpidfile)
		killcmd
	ctl delete
	exit
}

fn killcmd{
	log killcmd
	cmdpid=`{cat $cmdpidfile}
	echo kill >/proc/$cmdpid/notepg
	sleep .3
	addr '$'; ctl 'dot=addr'
	data Watch: killed
	ctl clean
}

@{
	rfork s

	if(~ $start y && ! ~ $"args '') echo Get

	# listen to Put on any window
	cat /mnt/acme/log | grep ' put '$rx | awk '{print "put" }' &
	# capture any pid in this process group
	xpid=$apid

	# filter/transform events
	cat $w/event >[2=1] |
	awk '/^Mx.* (Get|Kill|Del)/ {print $5; next}
		/^M[Xx][0-9]+ +[0-9]+ +[0-9]+ +0 *$/ {next}
		/^M[LlXx]/ {print $1 " " $2}'

	# kill our process group
	echo kill >/proc/$xpid/notepg
} >[2]/dev/null |
while(){
	msg=`{read}
	log msg: $msg
	switch($msg){
	case put Get
		if(! test -f $cmdpidfile){
			{
				log running
				prevstatus=''
				addr ,
				grep '^% ' $w/body |
				while(line=`{read | sed 's/^[% ]+//' | grep -v '^$'}){
					echo '%' $line
					status=$prevstatus
					if(~ $"prevstatus ''){
						rc -c $"line >[2=1]
						prevstatus=$status
						if(! ~ $"prevstatus '') echo '# status:' $prevstatus
					}
					if not{
						echo '# not run'
					}
				} >>$w/data &
				cmdpid=$apid
				log cmdpid: $cmdpid
				echo $cmdpid >$cmdpidfile
				wait $cmdpid

				log exited
				ctl clean
				sleep .1 # give the kill commands time to write where they want
				addr 0; ctl 'dot=addr'; ctl show
				rm $cmdpidfile
			}&
		}
	case Kill
		if(test -f $cmdpidfile)
			killcmd $msg
	case Del
		sigint
	case *
		log forwarding $msg
		echo $msg >$w/event
	}
}
sleep .1
exit ''