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#!/bin/sh
# This software is released into the public domain.
# It is provided "as is", without warranties or conditions of any kind.
# Anyone is free to use, modify, redistribute and do anything with this software.
# backlight brightness configuration utility
#
# Requirements: POSIX sh, backlight in /sys/class/backlight/*,
# write permission for $BACKLIGHT/brightness
set -eu
sys_backlight="/sys/class/backlight"
get_bldir() {
bldir=
if [ -n "${BACKLIGHT:-}" ]; then
bldir="$sys_backlight/$BACKLIGHT"
else
for f in "$sys_backlight"/*; do
if [ "$f" = "$sys_backlight/*" ]; then
printf "cannot find a backlight in %s\n" "$sys_backlight" >&2
exit 1
elif [ -n "$bldir" ]; then
printf "multiple backlights found, choose one with \$BACKLIGHT\n" >&2
exit 1
fi
bldir="$f"
BACKLIGHT="${f##*/}"
done
fi
}
read_num() {
read -r data <"$1"
if ! is_num "$data"; then
printf "expected a number reading '%s', but got '%s'\n" "$1" "$data" >&2
exit 1
fi
printf %d "$data"
}
is_num() {
case "$1" in
[0-9]) return 0 ;;
[0-9][0-9]) return 0 ;;
[0-9][0-9][0-9]) return 0 ;;
[0-9][0-9][0-9][0-9]) return 0 ;;
[0-9][0-9][0-9][0-9][0-9]) return 0 ;;
[0-9][0-9][0-9][0-9][0-9][0-9][0-9]) return 0 ;;
[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]) return 0 ;;
[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]) return 0 ;;
# hopefully it's not a >2^32 number
esac
return 1
}
get_brightness() {
raw_max="$(read_num "$bldir/max_brightness")"
raw_curr="$(read_num "$bldir/brightness")"
max=100
curr=$(( (raw_curr + (raw_max / 2 / max)) * max / raw_max ))
# brightness 0 tends to completely turn off the backlight
raw_min=1
case "$BACKLIGHT" in
nvidia_[0-9]*) raw_min=0 ;; # nvidia_0 at 0 is still not off
esac
}
get_raw_new() {
op="$1"
val="$2"
raw_new=
new=
if ! is_num "$val"; then
printf "expected a number for brightness, but got '%s'\n" "$val" >&2
exit 2
fi
case "$op" in
+) : $(( new = curr + val )) ;;
-) : $(( new = curr - val )) ;;
"") : $(( new = val )) ;;
=+) : $(( raw_new = raw_curr + val )) ;;
=-) : $(( raw_new = raw_curr - val )) ;;
=) : $(( raw_new = val )) ;;
*)
printf "invalid operator '%s'\n" "$op" >&2
exit 2
;;
esac
if [ -n "$new" ]; then
: $(( raw_new = new * raw_max / max ))
fi
if [ -n "$raw_new" ]; then
if [ "$raw_new" -gt "$raw_max" ]; then
raw_new="$raw_max"
fi
if [ "$raw_new" -lt "$raw_min" ]; then
raw_new="$raw_min"
fi
fi
}
set_brightness() {
get_raw_new "$1" "$2"
printf %d "$raw_new" > "$bldir/brightness"
}
usage() {
prog="$(basename "$0")"
printf "%s: usage: %s OPERATOR\n" "$prog" "$prog"
printf "\n"
printf "Operators:\n"
printf " (none) print current brightness in percentages\n"
printf " PERC set brightness to PERC percentages of max\n"
printf " +PERC increase brightness by PERC percentage points\n"
printf " -PERC decrease brightness by PERC percentage points\n"
printf " = print current brightness raw value\n"
printf " VAL set brightness to VAL raw value\n"
printf " =+VAL increase brightness by VAL raw value\n"
printf " =-VAL decrease brightness by VAL raw value\n"
printf "\n"
printf "Environment variables:\n"
printf " BACKLIGHT the backlight in %s/ to use\n" "$sys_backlight"
printf " (unnecessary if only one exists)\n"
}
main() {
if [ $# -gt 1 ]; then
usage >&2
exit 2
fi
if [ "${1:-}" = "-h" ] || [ "${1:-}" = "--help" ]; then
usage
exit
fi
get_bldir
get_brightness
op="${1:-}"
case "$op" in
"") printf "%d\n" "$curr" ;;
+[0-9]*) set_brightness + "${op#+}" ;;
-[0-9]*) set_brightness - "${op#-}" ;;
[0-9]*) set_brightness "" "$op" ;;
=) printf "%d\n" "$raw_curr" ;;
=+[0-9]*) set_brightness "=+" "${op#=+}" ;;
#+=[0-9]*) set_brightness "=+" "${op#+=}" ;;
=-[0-9]*) set_brightness "=-" "${op#=-}" ;;
#-=[0-9]*) set_brightness "=-" "${op#-=}" ;;
=[0-9]*) set_brightness "=" "${op#=}" ;;
*)
printf "invalid operator: '%s'\n" "$op" >&2
exit 2
esac
}
main "$@"
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