Bash IFS - Playing with Records - Part Two

   
   
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Article Series

This article series discuss more than 30 different programming languages. Please read overview before you read any of the details.

Playing with Records Related Articles.

Table of Content
Where to Discuss?

Local Group

Preface

Goal: Utilizing BASH IFS for string processing.

4: Approach in Solving Unique

A custom example, that you can rewrite.

An Algorithm Case

Why reinvent the wheel?

The same reason as other article.

x:xs Pattern Matching

The same with other article as well.

Exclude Function

Consider array in code below:

declare -a tags=(
  "60s" "jazz" "60s" "rock"
  "70s" "rock" "70s" "pop")

The exclude function is just a filter. We are going to remove array using diff ${tags[@]/$val}. With complete function as below

function exclude() {
  local val=$1
  shift
  local tags=("$@")
  
  local return=( ${tags[@]/$val} )
  echo "${return[@]}"
}

Finally we can call them in main script. and reformat the output using IFS.

# Extract output to array
tags_ex=$(exclude "rock" ${tags[@]})
IFS=' '; read -a tags_ar <<< "${tags_ex[@]}"
IFS=":"; echo "${tags_ar[*]}"

With the result as below array:

❯ ./11-exclude.sh
60s:jazz:60s:70s:70s:pop

BASH: Exclude Function

Recursive Unique Function

With exclude function above, we can build unique function recursively, as below code:

function unique() {
  local l_tags=("$@")

  if (( ${#l_tags[@]} <= 1 )); then
    echo "${l_tags[@]}"
  else
    local head=${l_tags[0]}
    local tail=${l_tags[@]:1}
    local exclude=( ${tail[@]/$head} )
    local uniq_temp=$(unique "${exclude[@]}")

    local return=($head)
    return+=(${uniq_temp[@]})
    echo "${return[@]}"
  fi
}

BASH: The Unique Function

Instead of using previously explained exclude function. We can just efficiently use array diff.

Applying Unique to Simple Array

Now we can apply the method to our unique song challenge.

source ./MyHelperUnique.sh

declare -a tags=(
  "60s" "jazz" "60s" "rock"
  "70s" "rock" "70s" "pop")

# Extract output to array
tags_un=$(unique ${tags[@]})
IFS=' '; read -a tags_ar <<< "${tags_un[@]}"
IFS=":"; echo "${tags_ar[*]}"

With the same result as below

BASH: Solving Unique Song

With the result as below array:

❯ ./12-unique-a.sh
60s:jazz:rock:70s:pop

Applying Unique to data Structure

We can also apply the method to our unique song challenge.

function unique() {
  local l_tags=("$@")

  if (( ${#l_tags[@]} <= 1 )); then
    echo "${l_tags[@]}"
  else
    local head=${l_tags[0]}
    local tail=${l_tags[@]:1}
    local exclude=( ${tail[@]/$head} )
    local uniq_temp=$(unique "${exclude[@]}")

    local return=($head)
    return+=(${uniq_temp[@]})
    echo "${return[@]}"
  fi
}

With the result as below array:

❯ ./12-unique-b.sh
60s:jazz:rock:70s:pop

BASH: Solving Unique Song

What is Next 🤔?

Consider continue reading [ Fish Shell - Playing with Records - Part One ].