Collapsing Function Examples and More!

collapsing_functions.sh

#!/usr/bin/env bash
# From Bash Hackers - http://wiki.bash-hackers.org/howto/collapsing_functions
# The first time you run chatter(), the function redefines itself based on the value of verbose. Thereafter, chatter doesn't check $verbose, it simply is.
# Further calls to the function reflect its collapsed nature. 
# If verbose is unset, chatter will echo nothing, with no extra effort from the developer.

[[ $1 = -v || $1 = --verbose ]] && verbose=1

chatter() {
  if [[ $verbose ]]; then
    chatter() {
      echo "$@"
    }
    chatter "$@"
  else
    chatter() {
      :
    }
  fi
}

echo "Waiting for 10 seconds."
for i in {1..10}; do
  chatter "$i"
  sleep 1
done

#2
if ! type _get_comp_words_by_ref >/dev/null 2>&1; then
_get_comp_words_by_ref ()
{
  echo booyah
}

collapsing_variable.sh

#!/usr/bin/env bash
# A collapsing function that enables or disables logging

# enable with 1 / disable with 0 (or anything else ;-)
declare -r LOG_ENABLE='1'

# TODO - something aint right with the date/time - "invalid number"
[[ 1 = $LOG_ENABLE ]] && declare -r logit='printf "%(%Y%m%d-%H:%M:%S)T %s\n" -1' || declare -r logit=':'

# Use $logit instead of printf / echo 
$logit "This is where the magic begins"