Are my usage functions implemented correctly?

Question

I have several functions in my ~/.bash_profile that I use as commands, and I've also created usage functions for them.

I'd like to know if I've implemented the usage functions correctly since I developed them on my own.

Example

IFS=$'\n'
usageSliceArr() {
  if [ $# != 3 ]; then
      echo 'name, index 1, index 2'
      return 1
  fi
 }
slicearr() {
  if (usageSliceArr $1 $2 $3); then 
      declare -n name=$1
      declare -i fst=$2 lst=$3
      echo ${name[@]:fst:lst}
  fi
 }

Answer 1

1. Double-quote your variables when you use them. Otherwise they'll break if you pass values that contain whitespace. Also, there's no need for that subshell. So instead of if (usageSliceArr $1 $2 $3); then you should write if usageSliceArr "$1" "$2" "$3"; then
2. Use -ne to compare numbers, != for strings
3. Don't forget there's https://shellcheck.net/
4. Double-quote your variables when you use them
5. Put the usage message inside the function that does the work, so that the code becomes self-documenting
6. Write error messages to stderr rather than stdout
7. Consider writing commands as shell scripts that live in your $PATH rather than functions available only if your ~/.bash_profile is executed
8. Did I mention you should double-quote your variables when you use them?

Here's one approach:

########################################################################
# slicearr name index count
#
# Return <count> space-separated and tokenised elements from the <name>
# array starting at <index>
#
slicearr() {
    if [ $# -ne 3 ]
    then
        echo 'Usage: name index count' >&2
        exit 1
    fi
declare -n name=$1
printf &quot;%s &quot; &quot;${name[@]:$2:$3}&quot;; echo

}

The relevance of the space-separated and tokenised clause applies to your original code, too. Consider an array

a=( one two 'twenty three' )

The "twenty three" will be extracted as a single element but returned as two space-separated values "twenty" and "three".

Answer 2

Using some good suggestions from @StéphaneChezalas, I'm going to do this now:

IFS=$'\n'
usageSliceArr() {
  if (( $# != 3 )); then
      echo 'name, index 1, index 2'
      return 1
  fi
 }
slicearr() {
  usageSliceArr $@ &&
    declare -n name=$1
    declare -i fst=$2 lst=$3
    echo ${name[@]:fst:lst}
 }

Bear in mind I have many functions including this one in my ~/.bash_profile it's not just a one off script.