1. 22
    sctd: a minimal 'daemon' for sct ☶ unix
    qbit avatar authored by qbit 1 year ago | 14 comments

A follow up to this post about @tedu’s sct utility.

It’s color setting is fairly close to the “redshift” app’s defaults.

#!/bin/sh

# Copyright (c) 2017 Aaron Bieber <aaron@bolddaemon.com>
#
# Permission to use, copy, modify, and distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

S=4500
INC=2
SCT=$(which sct)

if [ ! -e "$SCT" ]; then
    echo "Please install sct!"
    exit 1;
fi

function setHM {
    H=$(date +"%H" | sed -e 's/^0//')
    M=$(date +"%M" | sed -e 's/^0//')
    HM=$((${H}*60 + ${M}))
}

setHM

if [ $HM -gt 720 ]; then
    for i in $(jot $((1440 - $HM)));  do
        S=$((${S}+${INC}))
    done
else
    for i in $(jot $HM); do
        S=$((${S}+${INC}))
    done
fi

while true; do
    setHM

    if [ $HM -gt 720 ]; then
        S=$((${S}-${INC}))
    else
        S=$((${S}+${INC}))
    fi

    $SCT $S

    sleep 60
done

  1.  

  2. 4
    tb avatar tb edited 1 year ago | link

    You could simplify a bit and eliminate the two calls to jot(1) and the two for loops by doing this:

    if [ $HM -gt 720 ]; then
    S=$(( $S + $INC * (1440 - $HM) ))
else
    S=$(( $S + $INC * $HM ))
fi

    Running once a minute with an increment of 2 is a bit much since sct rounds the number to a precision of 500, so the sct call in the while loop will only do something once every 250 runs, i.e. roughly every 4 hours.

    Finally, since it wasn’t mentioned yet: jung@ polished it a bit and created an OpenBSD port of sct about a year ago.

    1. 1
      qbit avatar qbit 1 year ago | link

      Nice, thanks for the feedback!

      1. 1
        twk avatar twk 1 year ago | link

        Now sct is packaged for void linux as well, thanks to @duncaen. So it should be equally easy to get as the port.

      2. 2
        algernon avatar algernon 1 year ago | link

        Very small nitpick: this only works if /bin/sh is bash (or something that supports $((...))). Works like a charm after telling it to run with bash.

        I missed the original sct thread, and redshift felt heavy, so this little script + sct will be of great use to me. Thanks!

        1. 4
          alynpost avatar alynpost edited 1 year ago | link

          Piling on the nitpick wagon, error messages should go to stderr rather than stdout:

          - echo "Please install sct!"
+ echo >&2 "Please install sct!"
  exit 1;
          1. 2
            twk avatar twk 1 year ago | link

            FWIW, dash handles this properly as well:

            % file /bin/sh
/bin/sh: symbolic link to dash
% sh
$ echo $((1440 - 720))
720

            OpenBSD’s ksh, same goes for zsh:

            $ echo $((1440 - 720))
720

            So I guess on the majority of systems you’d run X on, this won’t be an issue ;)

            Now, my own nitpick - I’ve ran shellcheck and fixed some warnings:

            #!/bin/sh

# Copyright (c) 2017 Aaron Bieber <aaron@bolddaemon.com>
#
# Permission to use, copy, modify, and distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

S=4500
INC=2
SCT=$(which sct)

if [ ! -e "$SCT" ]; then
    echo "Please install sct!"
    exit 1;
fi

setHM() {
    H=$(date +"%H" | sed -e 's/^0//')
    M=$(date +"%M" | sed -e 's/^0//')
    HM=$((H*60 + M))
}

setHM

if [ $HM -gt 720 ]; then # t > 12:00
    for _ in $(jot $((1440 - HM)));  do
        S=$((S+INC))
    done
else # t <= 12:00
    for _ in $(jot $HM); do
        S=$((S+INC))
    done
fi

while true; do
    setHM

    if [ $HM -gt 720 ]; then
        S=$((S-INC))
    else
        S=$((S+INC))
    fi

    $SCT $S

    sleep 60
done

            Also note that on linux systems, the jot binary is often not available (I just discovered it today, it’s an OpenBSD utility). At least on void linux one can install it with the outils package.

            Either way, very useful - no need to run sct by hand now :)

            1. 2
              algernon avatar algernon 1 year ago | link

              Odd, my dash at home barfed on the script. I now checked again, and it errors out on function setHM { .. }: it wants setHM () { ... } instead.

              Not quite sure why I remember $((...)) being a problem…

              1. 1
                rjc avatar rjc 1 year ago | link

                function, even though technically a bashism, originated in ksh.

                In terms of $((...)) being a problem, you are most likely referring to ((...)) which is indeed a bashism. Alternatively, you might have come across ++ or -- in $((...)), which are not required by POSIX.

              2. 1
                qbit avatar qbit 1 year ago | link

                for _ in $(jot $((1440 - HM))); do

                huh, I had no idea _ was a thing, neat!

                1. 1
                  twk avatar twk 1 year ago | link

                  $_ holds the last argument of the preivously run command. Overwriting it does no harm here and in similar places, so I occasionally make use of it (both to silence shellcheck and to signal the value won’t be used). It’s possible though some folks might object :)

                2. 1
                  epilys avatar epilys 1 year ago | link

                  Also note that on linux systems, the jot binary is often not available (I just discovered it today, it’s an OpenBSD utility).

                  You can use seq instead of jot on linux.

                3. 1
                  voidzero avatar voidzero 1 year ago | link

                  In similar vein, I’d suggest to replace [ with [[ because the latter is a bash/zsh/dash builtin.

                  1. 1
                    duncaen avatar duncaen 1 year ago | link

                    Its a myth, you can check it with type [, both are builtin, [[ is only available in larger shells, [ is POSIX. The [ should be preferred for #!/bin/sh portability.

                  2. 1
                    rjc avatar rjc 1 year ago | link

                    $((…)) is very much POSIX.