Screen timeout/lock script

Question

This is a script I made while having trouble with xautolock and dimming of the screen right before locking it. I would like some tips for making it a bit more robust and to know of any disadvantages of it. I don't know how it works with multiple screens but I suspect it does not.

#!/bin/bash
# Lock screen in:
minutes=15
seconds=0
# How many seconds it takes to dim
dim_secs=5
idle_secs=$(( $minutes * 60 + $seconds )) # Screen timeout in seconds
idle_ms=$(( $idle_secs * 1000 ))
timeout=$idle_secs
while true; do
 sleep $timeout
 if pgrep xflock4 > /dev/null; then
 timeout=$idle_secs
 continue
 fi
 # After sleeping, check user idle time
 if [ $(xprintidle) -ge $idle_ms ]; then
 WINDOW=$(echo $(xwininfo -id $(xdotool getactivewindow) -stats | \
 egrep '(Width|Height):' | \
 awk '{print $NF}') | \
 sed -e 's/ /x/')
 SCREEN=$(xdpyinfo | grep -m1 dimensions | awk '{print 2ドル}')
 # If greater than timeout check if something's not in fullscreen and active
 if [ "$WINDOW" != "$SCREEN" ]; then
 interrupted=false # If dimming's been interrupted
 screen=$(xrandr -q | grep " connected" | awk '{print 1ドル;}') # Connected screen
 brightness=$(xrandr --verbose | grep -i brightness | cut -f2 -d ' ') # Current brightness
 start_time=$(date "+%s.%N") # Current time
 while true; do
 # Current brightness(0 to $brigtness), decided by time since dimming started
 br=$(echo "$brightness-$brightness*(($(date "+%s.%N")-$start_time)/$dim_secs)" | bc -l)
 if [ $(echo "$br >= 0" | bc) -eq 1 ]; then
 # Set the current brightness and sleep for a short while
 xrandr --output $screen --brightness $br
 sleep 0.01
 else
 # If brightness is less than 0 then it means that the
 # time since starting dimming is greater than $dim_secs
 break
 fi
 # If the user gave an input that's less than $idle_ms
 # Will always be less than $idle_ms if it was interrupted during dimming
 if [ $(xprintidle) -lt $idle_ms ]; then
 interrupted=true
 break
 fi
 done
 if $interrupted; then
 # If it was interrupted during dimming, reset brightness
 xrandr --output $screen --brightness $brightness
 else
 xset dpms force off # Turn screen off
 xrandr --output $screen --brightness $brightness # Reset brightness
 xflock4 # Lock screen
 fi
 fi
 fi
 # Timeout before checking idle time again
 timeout=$(echo "$idle_secs - $(xprintidle) / 1000 " | bc -l)
done

Answer 1

You don't need to prefix variables with $ inside $(( ... )), this will work just as well:

idle_secs=$(( minutes * 60 + seconds )) # Screen timeout in seconds
idle_ms=$(( idle_secs * 1000 ))

---

In many places you pipe to a grep and then pipe to awk. Note that awk can perform many of the functions of grep, and using one process (awk) instead of two (grep + awk) would be more optimal.

Here are some examples. Instead of:

... | egrep '(Width|Height):' | awk '{print $NF}'

This is equivalent:

... | awk '/(Width|Height):/ {print $NF}'

Instead of:

... | grep -m1 dimensions | awk '{print 2ドル}'

This is equivalent:

... | awk '/dimensions/ {print 2ドル; exit}'

And so on, similarly at other places too, you get the idea.

---

Another common pattern I see at many places:

echo "$br >= 0" | bc -l

That is, using echo to pass a string to a command. A better way is using here-strings, like this:

bc -l <<< "$br >= 0"

---

This long line appears at multiple places, sometimes with minor variations:

# If it was interrupted during dimming, reset brightness
xrandr --output $screen --brightness $brightness

It would be better to move this to a function, for example reset_brightness, to reduce duplication of logic.

• thabubble: I get "pgrep: invalid option -- 'q'"
• janos: Ah... Worked in my system (BSD version), looks like GNU version doesn't have it. Thanks, removed that point.