source: mpd-status/trunk/examples/status @ 34

#!/usr/lib/9base/bin/rc
# periodically print stuff to the bar

PIDFILE=/tmp/.ixp-$USER/statuspid-$WMII_IDENT

if(test -r $PIDFILE) {
    kill -2 `{cat $PIDFILE} >[2]/dev/null
}
echo $pid >$PIDFILE

mpdlab=`{wmiir read /bar/new}
wmiir write /bar/$mpdlab/b1press 'extern mpc prev'
wmiir write /bar/$mpdlab/b2press 'extern mpc toggle'
wmiir write /bar/$mpdlab/b3press 'extern mpc next'
wmiir write /bar/$mpdlab/b4press 'extern mpc volume -5'
wmiir write /bar/$mpdlab/b5press 'extern mpc volume +5'

# date and load average

label=`{wmiir read /bar/new}
wmiir write /bar/$label/b1press 'wmiir write /wm/ctl ''select prev'''
wmiir write /bar/$label/b3press 'wmiir write /wm/ctl ''select next'''
wmiir write /bar/$label/b4press 'wmiir write /wm/ctl ''select prev'''
wmiir write /bar/$label/b5press 'wmiir write /wm/ctl ''select next'''

# install signal handler for artificial sigexit:
fn sigint {
    if(test -f $PIDFILE && ~ `{cat $PIDFILE} $pid)
        rm -f $PIDFILE
    wmiir write /bar/ctl 'destroy '^$mpdlab
    wmiir write /bar/ctl 'destroy '^$label
    exit
}

fn mpdstatus {
    echo (`{python2.4 $HOME/.wmii/scripts/mpc.py})
}

fn statustext {
    # if you need a formatted date, use awk
    echo (`{date} `{uptime | sed 's/.*://; s/,//g'})
}

mpdtext=`{mpdstatus}
text=`{statustext}
while(wmiir write /bar/$mpdlab/data $"mpdtext >[2]/dev/null; wmiir write /bar/$label/data $"text >[2]/dev/null) {
    sleep 2
    mpdtext=`{mpdstatus}
    text=`{statustext}
}