Help me understand a thing or two

I am always asking more or less technical questions so I thought maybe I'll start my own thread where I can post about things I am trying to understand in the hope that some of you can share your knowledge, and perhaps some tutorage with me.

What am I trying to do:

I want my barscript.sh (that I am using with sdorfehs wm) to indicate when my speakers are muted.

What I've tried:

xev output of my ThinkPad X230's mute button is as expected: XF86AudioMute
However, because toggling the mute botton on/off outputs the exact same information, I figure I need to write a short script?

So, I discovered the commands to mute and unmute are:
mixerctl -w outputs.master3.mute=on
mixerctl -w outputs.master3.mute=off
So with absolutely little to no scripting knowledge, I whipped up this simple script:

mute.sh:

#!/bin/sh

MUTE=$(mixerctl outputs.master3.mute | sed 's/^outputs.master3.mute=//')

if [ "${MUTE}" = "off" ]; then
    RUN='mixerctl -w outputs.master3.mute=on'
else
    RUN='mixerctl -w outputs.master3.mute=off'
fi

exec "$RUN"

This is clearly where I'm going wrong because the script don't work!

Running mute.sh gives this error:
exec: mixerctl -w outputs.master3.mute=on: not found

Nevertheless, I added this keybinding to my wm config:
definekey top XF86AudioMute exec $HOME/.scripts/mute.sh

Running the command mixerctl -w outputs.master3.mute=on in a terminal works, and after adding the relevant bits to my barscript.sh I do get the desired output in my bar: [68%MUTE]. It's just the mute.sh script that isn't working and my lack of basic shell scripting is clearly the reason why.

For reference, my barscript.sh:

#!/bin/sh

while true; do

# Packages
PKGS="$(pkg_info | wc -l | sed -e 's/^[ \t]*//')"

# Volume
LEV="$(mixerctl outputs.master | sed -e 's|.*,||g')"
VOL="$name$(expr \( $LEV \* 100 \) / 254)"
MUTESTATE=$(mixerctl outputs.master3.mute | sed 's/^outputs.master3.mute=//')
if [ "${MUTESTATE}" = "on" ]; then
    MUTE=' MUTE'
else
    MUTE=''
fi

# Battery
BAT_PERC="$(envstat -s acpibat0:charge | tail -1 | sed -e 's,.*(\([ ]*[0-9]*\)\..*,\1,g')%"
BAT_STATE="$(envstat -d acpibat0 | awk 'FNR == 10 {print $2}')"
if [ "${BAT_STATE}" = "TRUE" ]; then
    STATE='+'
else
    STATE='-'
fi

# Date
D="$(date '+%a %d %b %I:%M')"

# Weather
WTTR="$(cat $HOME/.scripts/weather.txt)"

# Print
echo "$D ~ $WTTR [$PKGS#][$VOL%$MUTE][$STATE$BAT_PERC]" > ~/.config/sdorfehs/bar

sleep 1
done
exit 0

The output of barscript.sh is sent to ~/.config/sdorfehs/bar which is then read by the wm through some sort of unix wizardry which I don't understand.

I would love to know what I'm doing wrong or how this could be done better.

rvp Remove the exec and quotes around $RUN; or, use this somewhat shorter version:
#!/bin/sh
#
#Toggle audio mute state.
exec mixerctl -w outputs.master3.mute++

In that case I don't need a mute script at all, I've just remapped the mute button with:
definekey top XF86AudioMute exec mixerctl -w outputs.master3.mute++

This works
This also leads me to wonder, is ++ a universal argument for toggle on/off ?

rvp And, for barscript.sh, you don't need to use expr; just calculate it directly using $((...)).

I guess your talking about the VOL line:
VOL="$name$(expr \( $LEV \* 100 \) / 254)"

This was something that I stole from @pin when I was using his unibar config. I'm not exactly sure how you mean it should be calculated directly.

rvp Remove exec--it's only useful inside shell scripts.

Inside the sdorfehs config file exec is necessary. I don't know why, but this is how you set executable key bindings.

rvp LIke this--no expr needed in a POSIX shell:

This would explain why when I kill the X server I see a whole bunch of this:

...
expr: syntax error
expr: syntax error
expr: syntax error
expr: syntax error
expr: syntax error
...

EDIT: It took me a few shots to figure it out but I got there in the end with

VOL="$((( $LEV ) * 100 / 254))"

EDIT2: Still getting expr: syntax error after killing X server though

pin Do you use a dictionary to look-up all that stuff?

136 lines .shrc

haha yeah, mostly alias's. Is it better to use a separate file for Alias's? Believe it or not I remember most of them.
In a way, it's kind of a personal knowledge base for commands I would otherwise forget.

rvp
Wow, that's awesome thanks! I'll try it out

EDIT: Works like a charm

Now lets say I wanted to add uptime to the bar as well. In previous bar scripts I had used this line:

UP="$(uptime | awk -F, '{sub(".*up ",x,$1);print $1}' | sed -e 's/^[ \t]*//')"

Is there a neater/simpler way to get the same output without sed of awk ?

pin This is most probably unrelated.
I did try to look if I could find anything by taking a pick at your config files but, I gave-up straight away when I saw your .shrc

Any way of knowing which file is causing the error?

rvp ️ This does the trick. The only thing which is strange is, I like to encase each output in [square brackets] however when I do this I get a trailing space after the first bracket like so: [ 14 minutes]. This triggers my OCD slightly I've just added the bracked to the echo line at the end like this:

UP=$(uptime)
UP=${UP#*up}
UP=${UP%%,*}
echo [$UP]

yeti Nice! However, I shutdown my laptop when I'm done using it so no need for "days"

Ok, new query...

I'd like for my laptop to warn me when my battery is low. Visual notifications are useless and I would rather have an audible beep (which I noticed isn't available on NetBSD) or some other sound once the battery gets below 10%.

I guess a shell script could do this but would a system service need to be started at boot in order to monitor the battery status?

neubaer I thought about using cron but dont really want scripts running every minute if it isn't necessary. I think using a powerd scrips as RVP suggeests will work better.

rvp Awesome, thanks. Is there any way to use a built in hardware beep/bell rather than a .wav file?

rvp
I assumed I could just add this to the /etc/powerd/scripts/sensor_battery script like so but it didn't work.
Does it need to be called from a separate script?

#!/bin/sh -
#
#       $NetBSD: sensor_battery,v 1.8 2014/03/13 00:50:55 christos Exp $
#
# Generic script for battery sensors.
#
# Arguments passed by powerd(8):
#
#       script_path device event sensor state_description
#
case "${2}" in
normal)
        logger -p warning \
            "${0}: (${3}) capacity reached normal state [${1}]" >&1
        exit 0
        ;;
state-changed)
        logger -p warning "${0}: (${3}) state changed to ${4} [${1}]" >&1
        exit 0
        ;;
warning-capacity|warning-under)
        logger -p warning \
            "${0}: (${3}) capacity below warning limit [${1}]" >&1
        exit 0
        ;;
critical-capacity|critical-under)
        logger -p warning \
            "${0}: (${3}) capacity below critical limit [${1}]" >&1
        echo -n C >/dev/speaker
        exit 0
        ;;
warning-over)
        logger -p warning \
            "${0}: (${3}) capacity above warning limit [${1}]" >&1
        echo -n CD >/dev/speaker
        exit 0
        ;;
        critical-over)
        logger -p warning \
            "${0}: (${3}) capacity above critical limit [${1}]" >&1
        exit 0
        ;;
high-capacity)
        logger -p warning \
            "${0}: (${3}) capacity above high limit [${1}]" >&1
        exit 0
        ;;
maximum-capacity)
        logger -p warning \
            "${0}: (${3}) capacity above maximum limit [${1}]" >&1
        exit 0
        ;;
#
# This event is _ONLY_ received when all AC Adapters are OFF and all
# batteries on the system are in CRITICAL or LOW state.
#
# It is not recommended to remove the shutdown call.
#
low-power)
        logger -p warning "${0}: LOW POWER! SHUTTING DOWN." >&1
        /sbin/shutdown -p now "${0}: LOW POWER! SHUTTING DOWN."
        echo -n CDEF >/dev/speaker
        exit 0
        ;;
*)
        logger -p warning "${0}: unsupported event ${2} on device ${1}" >&1
        exit 1
        ;;
esac