Creating classes and objects using bash scripting

Question

I'm trying to use bash scripting to make an script act like a phone book, so i tried to create classes and objects but unfortunately i couldn't find a way to do that ! so i'm asking how to create a class using bash scripting??

Answer 1

You can try to do something like this

example.sh

#!/bin/bash

# include class header
. obj.h
. system.h

# create class object
obj myobject

# use object method
myobject.sayHello

# use object property
myobject.fileName = "file1"

system.stdout.printString "value is"
system.stdout.printValue myobject.fileName

obj.h

obj(){
    . <(sed "s/obj/$1/g" obj.class)
}

obj.class

# Class named "obj" for bash Object

# property
obj_properties=()

# properties IDs
fileName=0
fileSize=1

obj.sayHello(){
    echo Hello
}

obj.property(){
    if [ "$2" == "=" ]
    then
        obj_properties[$1]=$3
    else
        echo ${obj_properties[$1]}
    fi
}

obj.fileName(){
    if [ "$1" == "=" ]
    then
        obj.property fileName = $2
    else
        obj.property fileName
    fi
}

system.h

. system.class

system.class

system.stdout.printValue(){
    echo $($@)
}

system.stdout.printString(){
    echo $@
}

Link for reference: https://github.com/mnorin/bash-scripts/tree/master/objects The point is you can't create objects but you can emulate object-oriented programming in bash

Answer 2

So I remember checking this question and answer a few years back .. and was thinking.... WHAT!?!?!

Then last week I took a closer look at @Maxims answer and then it became clear..

I have spent the last week and created a bash class transpiler and class loader for class object, with methods and other goodies.. all cause I wanted to create a terminal animation infrastructure:

So while this is just a start I found this to be a SUPER cool and challenging adventure.. I hope my code would help someone else as well!!

BTW: Was tested only on MAC OS so some tweaking might be needed :)

Answer 3

While there's no true way to create classes in Bash, you can get a little creative. I've found over the years that my preferred way to do this is to create a function that returns a command that can be executed to change state or read properties of the instance. The instance data can be stored in an array.

For example, if you wanted to make a class for binary search trees, you could have this in BinarySearchTree.sh:

__BINARYSEARCHTREE_INSTANCE_DATA__=()

__BINARYSEARCHTREE_INSTANCE_DATA_LENGTH__=()
__BINARYSEARCHTREE_INSTANCE_DATA_SIZE__=()

BinarySearchTree()
{
    echo "__BinarySearchTree__ $RANDOM "
}

__BinarySearchTree__()
{
    local id="$1"
    local code="$2"

    case "$code" in
        '.insert' | '[insert]' | "['insert']" | '["insert"]')
            local value="$3"

            if [ "${__BINARYSEARCHTREE_INSTANCE_DATA__["$id", 0] + set}" ]; then
                local length="${__BINARYSEARCHTREE_INSTANCE_DATA_LENGTH__["$id"]}"
                local new_node="$length"

                __BINARYSEARCHTREE_INSTANCE_DATA__["$id", "$length"]="$value"

                length=$((length + 1))
                __BINARYSEARCHTREE_INSTANCE_DATA__["$id", "$length"]=''

                length=$((length + 1))
                __BINARYSEARCHTREE_INSTANCE_DATA__["$id", "$length"]=''

                local current_node=0
                local parent

                while [ 1 ]; do
                    parent="$current_node"

                    if [ "$value" -lt "${__BINARYSEARCHTREE_INSTANCE_DATA__["$id", "$((current_node))"]}" ]; then
                        current_node="${__BINARYSEARCHTREE_INSTANCE_DATA__["$id", "$((current_node + 1))"]}"

                        if [ "$current_node" == '' ]; then
                            __BINARYSEARCHTREE_INSTANCE_DATA__["$id", "$((parent + 1))"]="$new_node"

                            break
                        fi
                    else
                        current_node="${__BINARYSEARCHTREE_INSTANCE_DATA__["$id", "$((current_node + 2))"]}"

                        if [ "$current_node" == '' ]; then
                            __BINARYSEARCHTREE_INSTANCE_DATA__["$id", "$((parent + 2))"]="$new_node"

                            break
                        fi
                    fi
                done

                __BINARYSEARCHTREE_INSTANCE_DATA_LENGTH__["$id"]="$((length + 1))"
                __BINARYSEARCHTREE_INSTANCE_DATA_SIZE__["$id"]="$((${__BINARYSEARCHTREE_INSTANCE_DATA_SIZE__["$id"]} + 1))"
            else
                __BINARYSEARCHTREE_INSTANCE_DATA__["$id", 0]="$value"
                __BINARYSEARCHTREE_INSTANCE_DATA__["$id", 1]=''
                __BINARYSEARCHTREE_INSTANCE_DATA__["$id", 2]=''
                __BINARYSEARCHTREE_INSTANCE_DATA_LENGTH__["$id"]=3
                __BINARYSEARCHTREE_INSTANCE_DATA_SIZE__["$id"]=1
            fi;;

        '.has' | '[has]' | "['has']" | '["has"]')
            local value="$3"

            local current_node=0

            if [ "${__BINARYSEARCHTREE_INSTANCE_DATA__["$id", 0] + set}" ]; then
                while [ 1 ]; do
                    local current_value="${__BINARYSEARCHTREE_INSTANCE_DATA__["$id", "$((current_node))"]}"

                    if [ "$current_value" == "$value" ]; then
                        return 0
                    fi

                    if [ "$value" -lt "$current_value" ]; then
                        current_node=${__BINARYSEARCHTREE_INSTANCE_DATA__["$id", "$((current_node + 1))"]}
                    else
                        current_node=${__BINARYSEARCHTREE_INSTANCE_DATA__["$id", "$((current_node + 2))"]}
                    fi

                    if [ "$current_node" == '' ]; then
                        return 1
                    fi
                done
            else
                return 1
            fi;;

        '.size' | '[size]' | "['size']" | '["size"]')
            if [ "${__BINARYSEARCHTREE_INSTANCE_DATA__["$id", 0] + set}" ]; then
                echo "${__BINARYSEARCHTREE_INSTANCE_DATA_SIZE__["$id"]}"
            else
                echo 0
            fi;;

        '.empty' | '[empty]' | "['empty']" | '["empty"]')
            if [ "${__BINARYSEARCHTREE_INSTANCE_DATA__["$id", 0] + set}" ]; then
                return 1
            else
                return 0
            fi;;

        '.clear' | '[clear]' | "['clear']" | '["clear"]')
            unset "__BINARYSEARCHTREE_INSTANCE_DATA__[$id, 0]"
    esac
}

And then make objects like this:

source './BinarySearchTree.sh'

process()
{
    local tree="$1"

    $tree.insert 52
    $tree.insert -150
    $tree.insert 42

    if $tree.has 42; then
        echo 'Has 42!'
    else
        echo 'Does not have 42!'
    fi

    $tree.clear

    echo "Size: $($tree.size)"
}

main()
{
    local tree=$(BinarySearchTree)

    process "$tree"
}

main "$#" "$@"

The advantages of this method are that objects can be passed into other functions and there are no external file operations. Even though this may seem impractical, it actually makes Bash quite a nice language to work in since you can modularize your classes.

Answer 4

Try with BashX: https://github.com/reduardo7/bashx (This is my project, I use it on several other projects)

Example

#!/usr/bin/env bash

# ...

@Actions.action1() { # \\n Action without arguments
  set -x
  pwd
  @log "
  Action 1
  Multi-Line
"
  ls -la
  bash
}

@Actions.action2() { # param1 [param2] \\n Action with arguments\\n\\tdescription second line\\nother line
  eval "$(@user.options 'new:-n|-N' 'path:-p|--path:true')"
  set -x

  @log "'n' or 'N' parameter: ${user_options_new}"
  @log "'p' or 'path' parameter: ${user_options_path[@]} (${#user_options_path[@]})"

  local param1="$1"
  local param2="$2"
  [[ "$param1" != 'asd' ]] && @throw.invalidParam param1

  @log Action 2
  @log Param1: $1
  @log Param2: $2
}

@app.run "$@"

Usage

./myscript action1
./myscript action2 -n -p /tmp 'my param 1'