A shell script to determine which physical screen it's running on

I was working on a program to generate storyboard files from movies, and wanted the storyboard canvas to track the screen size. In order to do that I needed to know which screen the program was running on, since I generally have two on my system (the laptop screen and an external monitor.)

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#!/bin/bash
# Generate a window name as random as I can make it
X_NAME="$(echo "$(date +%t)-$RANDOM" | sha1sum | cut -c1-8)"

# Start xlogo, iconified
xlogo -iconic -name $X_NAME & XLOGO_PID=$!
sleep 0.1   # Give xlogo enough time to set up its window

# Determine the xlogo's window position using 'xwininfo' and the following two
# lines from its output:
#   Absolute upper-left X:  3337
#   Absolute upper-left Y:  29
# The awk program prints "XLOGO_X=# XLOGO_Y=#" on stdout, which is then passed
# to 'eval' to set up environment variables of the same name
eval "$(xwininfo -name $X_NAME | 
  awk '/Absolute upper-left/ { match($0, /([XY]):/, a); print "XLOGO_" a[1] "=" $4 }')"

# Use xrandr to get the screens and their positions; for example:
#   eDP1 connected primary 1600x900+1920+0 (normal left inverted right x axis y axis) 382mm x 214mm
#   HDMI1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 598mm x 336mm
# Send this information along with XLOGO_X and XLOGO_Y to determine the screen
# that xlogo is running on, then write "SCREEN_WIDTH=# SCREEN_HEIGHT=#" on
# stdout. stdout is run through 'eval' to set up environment variables of the
# same name.
eval "$(xrandr | awk -v xlogo_x=$XLOGO_X -v xlogo_y=$XLOGO_Y '/^[^ ]+ *connected/ {
# Get <height>x<width>+<xstart>+<ystart>
    match($0, /([0-9]+)x([0-9]+)\+([0-9]+)\+([0-9]+)/, a)
    x_start = a[3]; x_end = a[1] + a[3]
    y_start = a[4]; y_end = a[2] + a[4]
    if (xlogo_x >= x_start && xlogo_x < x_end && xlogo_y >= y_start && xlogo_y < y_end) {
        print "SCREEN_WIDTH=" a[1] " SCREEN_HEIGHT=" a[2]
        exit
    }
}')"
kill $XLOGO_PID &>/dev/null

# Print the results for the edification of the user
echo "Width=$SCREEN_WIDTH  Height=$SCREEN_HEIGHT"



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