Bash script to swap monitor configurations

toggle_displays.bash

#!/usr/bin/env bash

# Sometimes mac os assigns different ids to external monitors. The ids can swap back and forth (based on 
# the order in which they are attached?). When the ids of two displays are switched, it's impossible
# (as far as I know) to determine which external monitor id goes with which physical device. Instead,
# this script just assumes the ids are backwards and switches the configuration for them.
# After all, you are calling the scripit, so something must be wrong...
#
# Note that this script depends heavily on the text output of displayplacer, so it may be somewhat brittle...

built_in_id=$(displayplacer list | grep -iB2 ' *Type *:.*built *in' | grep -i '^Persistent *screen *id' | sed -E 's/^[^:]*: *//g')

# Everything that is not a built-in is an external display
ext_ids=$(displayplacer list | grep -i '^Persistent *screen *id' | grep -v "$built_in_id" | sed -E 's/^[^:]*: *//g')

# Assuming two external displays:
first_ext_id=$(echo "$ext_ids" | sort | head -n1)
second_ext_id=$(echo "$ext_ids" | sort -r | head -n1)

# Get the current display config, swap the external display ids, and rerun it
my_config="$(displayplacer list | grep -E '^ *displayplacer *')"
toggle_config=$(echo "$my_config" | sed "s/${first_ext_id}/frogdinosaurcat/g")
toggle_config=$(echo "$toggle_config" | sed "s/${second_ext_id}/${first_ext_id}/g")
toggle_config=$(echo "$toggle_config" | sed "s/frogdinosaurcat/${second_ext_id}/g")
eval $toggle_config

@xdhmoore Thanks a lot for that script! Made my day!

Thanks a lot for providing the script. I needed to fix recognition of internal monitor (-iB3) and handle case when lid is closed. Here my updated script if anyone else needs this:

#!/usr/bin/env bash

# Sometimes mac os assigns different ids to external monitors. The ids can swap back and forth (based on 
# the order in which they are attached?). When the ids of two displays are switched, it's impossible
# (as far as I know) to determine which external monitor id goes with which physical device. Instead,
# this script just assumes the ids are backwards and switches the configuration for them.
# After all, you are calling the scripit, so something must be wrong...
#
# Note that this script depends heavily on the text output of displayplacer, so it may be somewhat brittle...

built_in_id=$(displayplacer list | grep -iB3 ' *Type *:.*built *in' | grep -i '^Persistent *screen *id' | sed -E 's/^[^:]*: *//g')

# Everything that is not a built-in is an external display
if [[ -n "$built_in_id" ]]; then
  ext_ids=$(displayplacer list | grep -i '^Persistent *screen *id' | grep -v "$built_in_id" | sed -E 's/^[^:]*: *//g')
else
  ext_ids=$(displayplacer list | grep -i '^Persistent *screen *id' | sed -E 's/^[^:]*: *//g')
fi

# Assuming two external displays:
first_ext_id=$(echo "$ext_ids" | sort | head -n1)
second_ext_id=$(echo "$ext_ids" | sort -r | head -n1)

# Get the current display config, swap the external display ids, and rerun it
my_config="$(displayplacer list | grep -E '^ *displayplacer *')"
toggle_config=$(echo "$my_config" | sed "s/${first_ext_id}/frogdinosaurcat/g")
toggle_config=$(echo "$toggle_config" | sed "s/${second_ext_id}/${first_ext_id}/g")
toggle_config=$(echo "$toggle_config" | sed "s/frogdinosaurcat/${second_ext_id}/g")
eval $toggle_config