rwxrob-dot/scripts/x_cmds

#!/usr/bin/bash

if [[ -z "$1" ]]; then
  mapfile cmds < /dev/stdin
else
  mapfile cmds < "$1"
fi

for cmd in "${cmds[@]}"; do
  [[ $cmd =~ ^x_[_a-zA-Z0-9]* ]] && echo "${BASH_REMATCH[0]}"
done