Retrieving input argument at index via alias in zsh

Question

I am trying to create functions and aliases in ZSH that make parameters handling easier to read.

As such, I wanted to create things like the example below:

#!/bin/zsh
myCustomFunction(){
  local numberOfParameters=$(count-parameters)
  local lastParameter=$(get-parameter $numberOfParameters)
  echo "Number of parameters: $numberOfParameters"
  echo "Last parameter is: $lastParameter"
}

Where count-parameters is defined below:

#!/bin/zsh
alias count-parameters='echo "$#"

How would I be able to implement get-parameter? I have been trying with "$@", as suggested in here, but that does not seem to work.

My desired result is that given an input such as:

myCustomFunction.sh "First param" "Second param" "Third param"

The output would be:

Number of parameters: 3
Last parameter: Third param

Answer 1

Through trial and error, I was able to accomplish the desired result.

Here's how I did it.

1. Count parameters alias

#!/bin/zsh
alias count-parameters='echo "$#"'

For get-parameter, I had to perform multiple operations (hacky way but it works)

• Save each parameter in a file (each parameter separated by the NUL character)
• Store the text within the file in a variable and loop over each character. Use the NUL character to determine where one parameter finishes and the next begins. Then, remove the file that was temporarily created

#!/bin/zsh
export tempParameterFile="$HOME/.params.txt"
alias save-parameters='save_parameters "$@"'

#!/bin/zsh
save_parameters(){
  numberOfParams=${#}
  if [ "$numberOfParams" -gt 0 ]; then
    rm -f "$tempParameterFile"
    while (( $# ))
    do
      echo -n "$1" >> "$tempParameterFile"
      echo -ne $'\0' >> "$tempParameterFile" # Adding NUL character after each parameter
      shift
    done
  fi
}

#!/bin/zsh

get_parameter(){
  local indexToUse=$1
  #echo "Called get_parameter for index $1"
  local currentIndex=0
  local nullCharacter=$'\0'
  local currentParam=""
  local allParameters=$(cat "$tempParameterFile")
  local currentCharacter=""
  for (( index=0; index<${#allParameters}; index++ ));
  do
    currentCharacter="${allParameters:$index:1}"
    if [ "$currentCharacter" = "$nullCharacter" ]; then # When the null character is found
      if [ "$currentIndex" = "$indexToUse" ];then # If the current index matches the desired index
        echo "$currentParam" # We found the word we were looking for
        return 0
      else # If the current index is lower than the desired index
        currentIndex=$(( $currentIndex + 1 )) # We increase the current index
        currentParam="" # And reset the current parameter
      fi
    else # If the character read is not  the null character
      currentParam="$currentParam$currentCharacter" # We append the character to the current param
    fi
  done
}

#!/bin/zsh
alias get-parameter='save_parameters "$@" && get_parameter'

When running the command:

╰─$ myCustomFunction.sh "One param" "Second param" "Third param" "Fourth param"
Number of parameters: 4
Last parameter: Fourth param

The desired result is achieved.

EDIT: Updated code to address the possibility of an input parameter having a new line in it. Now using, as suggested in the comments, the NUL character to differentiate between parameters.