I have a shell script like this 
    declare -x KBD_DEV="/dev/input/$event"
    KBDCFG=$(envsubst < /home/vincent/.config/kmonad/$config)
    kmonad <(echo "$KBDCFG") &

[download]
It's for kmonad to run config when new event found, config have to contain variable like this 
  input  (device-file "$KBD_DEV")

[download]
now I want to write it with perl, Is there an elegant way to do the same work of 'envsubst' and <(...) process substitution of shell, no need to use temp file and edit file.

In reply to how perl do 'envsubst' by vincentaxhe

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