Shell scripting in macOS – Part 8: Arrays & Dictionaries

/ Arun Patwardhan

This article is a continuation of the previous article. We will be taking the previous script and using it to build on the concepts we will learning in this article.

So far we have been working with a single piece of data. This was stored in a single variable. For each new piece of information we created a new variable. However, we often come across situations where there is more than one value for a given item. This is where collections like arrays and dictionaries come in.

Arrays

An array is a sequential collection of data. It allows us to store more than one value in a variable. This is good for situations like the contents of a folder, list of users, list of applications. Creating, reading, modifying, and iterating over an array is very easy. Let us have a look.

Creating

To create an array simply declare a variable followed by the '=' operator followed by values within round brackets.

# Declaring an array of items 
items=("ABC" "DEF" "GHI" "JKL" "MNO" "PQR")

Note that if you assign another set of values to the items variable it will replace the original values. We will see how to add values to an existing array a little later in the article.

Reading

We need to use the ${ } to read an array. This expands the array and allows us to read different values. There are different operations possible. I have listed some of those in the code snipper below.

# Getting a specific element from the array
echo "\${items[0]} 		= ${items[0]}"

# Getting all the elements of the array
echo "\${items[@]} 		= ${items[@]}"

# Getting the count of the elements in the array
echo "\${#items[@]} 	= ${#items[@]}"

# Getting a range of values
echo "\${items[@]:3:2} 	= ${items[@]:3:2}"

Modifying

To modify we simply need to use the '+' operator before the equals. This will add the value to the existing array without disturbing the other values.

# Pushing a value into the array
items+=("STU")

# Remove a specific item
unset items[2]

A small point to note. The unset is available with /bin/sh interpreter.

Iterating

for entry in "${items[@]}"
do 
	echo "-> $entry"
done

Here is a nice example of the user of arrays. The output of the list command is stored as an array in the variable named ‘directories’. Then using the for loop we can step through each folder and in turn printing its contents out.

directories=($(ls $HOME))

for folder in "${directories[@]}"
do 
	echo $folder
	eval "ls -l $HOME/$folder"
done

Dictionaries

Dictionaries are also collections just like arrays. However, there is one major difference. While arrays are indexed using integers, dictionaries are indexed using strings.

There is one small thing to note about dictionaries. They only work with bash version 4.0 or later. So if you face issues, make sure you are running bash 4.0 or later. In my example I am using zsh version 5.8.1. To find out which version you are running simply run the following command in terminal:

bash --version

or

zsh --version

Let us look at how to create and use dictionaries.

Creating

Creating a dictionary is very easy. We simply declare an associative array and give the dictionary variable a name.

declare -A contactDetails

Modifying

Editing or adding values to a dictionary is easy too. We use the variable name followed by the '[]' index brackets with the key value inside the brackets. This is followed by the '=' operator and the value to be assigned for that key after that.

contactDetails[name]="Arun"
contactDetails[email]="arun@amaranthine.co.in"
contactDetails[website]="www.amaranthine.in"
contactDetails[blog]="www.arunpatwardhan.com"
contactDetails[phone]="+91-9821000000"
contactDetails[dob]="$(date)"

Reading

We use the ‘@{ }’ operator to expand and read values from the dictionary, just as we did with an array. The only additional detail here is that we are using the key in order to get the specific value.

# Getting the value for a specific key
echo ${contactDetails[name]}

# Getting all the values
echo ${contactDetails[@]}

# Getting all the keys
echo ${(k)contactDetails[@]}

# Getting all the values
echo ${(v)contactDetails[@]}

# Getting all the keys and values
echo ${(kv)contactDetails[@]}

# Getting number of entries
echo ${#contactDetails[@]}

Iterating

There are several different ways of iterating over a dictionary. In the example below, the for loop is iterating over all the keys from the dictionary. Inside the loop we are using each key to extract the corresponding value.

for item in "${(k)contactDetails[@]}"
do 
	printf "%-10s \t%-40s" $item ${contactDetails[$item]}
	echo " "
done

Script

Let us update out script to use arrays.

#!/bin/zsh

#-------------------------------------------------------------------------------------------------
#NAME:		Folder creator
#AUTHOR:	Arun Patwardhan
#CONTACT:	arun@amaranthine.co.in
#DATE:		15th September 2022
#WEBSITE:	https://github.com/AmaranthineTech/ShellScripts
#-------------------------------------------------------------------------------------------------

#LEGAL DISCLAIMER --------------------------------------------------------------------------------
#THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
#IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
#FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
#AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
#LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
#OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
#SOFTWARE.
#-------------------------------------------------------------------------------------------------

#LICENSE/TERMS AND CONDITIONS --------------------------------------------------------------------
#MIT License

#Copyright (c) Amaranthine 2021.

#Permission is hereby granted, free of charge, to any person obtaining a copy
#of this software and associated documentation files (the "Software"), to deal
#in the Software without restriction, including without limitation the rights
#to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
#copies of the Software, and to permit persons to whom the Software is
#furnished to do so, subject to the following conditions:

#The above copyright notice and this permission notice shall be included in all
#copies or substantial portions of the Software.
#-------------------------------------------------------------------------------------------------

#ABOUT -------------------------------------------------------------------------------------------
# fileCreator.zsh
# 1.7
#-------------------------------------------------------------------------------------------------

#DESCRIPTION ------------------------------------------------------------------------------------- 
# - THis script is intended for creating the custom folders that are required on all corporate computers. 
# - Run this script on a new computer or a computer being reassigned to another employee.
# - This script can run on all computers.
#-------------------------------------------------------------------------------------------------

#USAGE -------------------------------------------------------------------------------------------
# - To create folders with default names run the command: ./folderCreator.zsh
# - To define your own folder names: ./folderCreator.zsh <folder1> <folder2> <folder3>
# - Available options  : Only the help option is available
# - Getting help       : Use the -h or the -help options to get more information. Or you can use the man command to view the man page.
#-------------------------------------------------------------------------------------------------

#WARNING/CAUTION ---------------------------------------------------------------------------------
#******************************************************************************************************************
#******************************************************************************************************************
#******************************************************************************************************************
#******************************************************************************************************************
# This script doesn't perform any validation of the folder names being passed in by the user. 
# If the script does not see the -h or the -help options then it will assume that the data being passed in is the name of the folder.
# The user of the script must ensure that the desired folder names are passed in.
#******************************************************************************************************************
#******************************************************************************************************************
#******************************************************************************************************************
#******************************************************************************************************************
#-------------------------------------------------------------------------------------------------

#INSTALLATION ------------------------------------------------------------------------------------
# Instructions for placing the script in the correct place are listed here. 
# Location:		/Library/Scripts/
# Permissions:	rwx r-x r-x
#-------------------------------------------------------------------------------------------------

#REQUIREMENTS ------------------------------------------------------------------------------------
# Shell:		/bin/zsh
# OS:			macOS Big Sur 11.4 or later
# Dependencies:	None
#-------------------------------------------------------------------------------------------------

#HELP/SUPPORT ------------------------------------------------------------------------------------
# You can get help by running the following commands.
# ./folderCreator.zsh -h
# ./folderCreator.zsh -help
# OR
# man folderCreator.zsh
# You can also view the log file for the same at: ~/Library/Logs/folderCreator_log_v1-7.log
#-------------------------------------------------------------------------------------------------

#HISTORY -----------------------------------------------------------------------------------------
# ------------------------------------------------------------------------------------------------
# Version 1.0: Basic script which creates the folders
# Version 1.1: Gives user the ability to specify the folder names at run time.
# Version 1.2: Adds safety checks to the scripts
# Version 1.3: Includes documentation as well as ability to get help.
# Version 1.4: Includes optimisation using for loop
# Version 1.5: Prompts the user in the GUI for names for the different folders.
# Version 1.6: Updated the log mechanism with the help of a function and here document.
# Version 1.7: Replaced the folder variables with an array
#-------------------------------------------------------------------------------------------------

#-------------------------------------------------------------------------------------------------
# ------------------------------ SCRIPT STARTS HERE ----------------------------------------------
#-------------------------------------------------------------------------------------------------
#-------------------------------------------------------------------------------------------------
#-------------------------------------------------------------------------------------------------

#These are the default values used for the folder names incase the user doesn't provide any.
FOLDERS=("Tools" "Reports" "Help")

#Script version number
VERSION_NUMBER="1.7"

#Command name
COMMAND_NAME="folderCreator.zsh"

#1. Check to see if the user is asking for help. In which case we will have to provide information about the command.
if [[ $1 == "-h" ]] || [[ $1 == "-help" ]]; then
	echo "ABOUT 
-----
fileCreator_v1-7.zsh
Version $VERSION_NUMBER

NAME 
----
$COMMAND_NAME — Folder creation utility SYNOPSIS
$COMMAND_NAME folder names [ verbs ]

DESCRIPTION 
-----------
$COMMAND_NAME creates 3 folders in the home folder. In case the folder names are not provided then the command will create folders with default names 'Tools', 'Reports', \"Help\".

There is also the option of getting help via the help verb.
- This script is intended for creating the custom folders that are required on all corporate computers. 
- Run this script on a new computer or a computer being reassigned to another employee.
- This script can run on all computers.

VERBS 
-----
[ −h −help] Both the options are used to invoke the help documentation.
[ −v −version] Both the options are used to get the version number of the folderCreator command.

REQUIREMENTS 
------------
The following are the minimum requirements to get the script running.
Shell:\t\t zsh
OS:\t\t macOS Big Sur 11.4 or later
Dependencies:\t None

INSTALLATION 
------------
$COMMAND_NAME can be installed anywhere you wish. However, there are certain locations that are recommended.
Location:\t /Library/Scripts/ 
Permissions: \t rwxr-xr-x

USAGE  
-----
$COMMAND_NAME folder1 folder2 folder3 
Will create folders with your own names. 

$COMMAND_NAME -h OR $COMMAND_NAME -help 
Will invoke the help utility.

$COMMAND_NAME -v OR $COMMAND_NAME -version 
will print the version number in stdout.

WARNING/CAUTION  
---------------
$COMMAND_NAME does not perform any validation of names. The only options that folderCreator accepts are -h and -help verbs or the -v and 
-version verbs. If the script does not see the -h , -help or the -v , -version options then it will assume that the data being passed in is 
the name of the folder. The user of the folderCreator command must ensure that the desired folder names are passed in. The user will also be 
prompted, via the graphical user interface, if he/she wishes to provide the names for the folders. If yes, then there will be subsequent 
prompts asking for the folder names.

EXAMPLES 
--------
$COMMAND_NAME Resources Results Assistant
This will create 3 folders Resources , Results , Assistant , in the user’s home folder. 

$COMMAND_NAME
This will create 3 folders with the default names

$COMMAND_NAME Apps
This will use the Apps name for the first folder but the default names for the last 2 folders. 

NOTE
----
The user will be asked if he/she wishes to provide custom names in all the examples mentioned above. The user's value will always override 
whatever is being provided to the script or defaults.

DIAGNOSTICS 
-----------
The script produces a log file called ~/Library/Logs/folderCreator_log_v1-x.log
This file is typically located in the user’s home folder log folder. The x represents the version number of $COMMAND_NAME
You can view the logs for each respective version.

COPYRIGHT  
---------
Copyright (c) Amaranthine 2015-2021. All rights reserved. https://amaranthine.in

EXIT STATUS  
-----------
In most situations, $COMMAND_NAME exits 0 on success"
	exit 0
fi

PATH_TO_LOG="$HOME/Library/Logs/folderCreator_log_v1-7.log"

# Function to log activity
function recordActivity() {
	cat << EOF >> $PATH_TO_LOG
[$(date)] $1
EOF
}


echo "$(date) Running script $0 to create folders."
echo ""

TODAY=$(date)

recordActivity "Starting"

#2. Check to see if the version number is 
if [[ $1 == "-version" ]] || [[ $1 == "-v" ]]; then
	echo "Version: $VERSION_NUMBER"
	exit 0
fi

#3. The following if statements check to see if the script is receiving any arguments. It then picks those arguments and assigns them to the respective variables for use in the script.
if [[ $1 != "" ]]; then
	FOLDERS[0]=$1
fi

if [[ $2 != "" ]]; then
	FOLDERS[1]=$2
fi

if [[ $3 != "" ]]; then
	FOLDERS[2]=$3
fi

#4. We can prompt the user to see if they wish to provide folder names themselves. This will override any values provided as arguments.
userClicked=$(/usr/bin/osascript -e 'button returned of (display dialog "Would you like to provide names for the folders or use the defaults instead?" buttons {"Custom", "Default"} default button 2 with icon POSIX file "/System/Library/CoreServices/HelpViewer.app/Contents/Resources/AppIcon.icns")')
	
# if the user decides to provide custom names then go ahead and ask the user via GUI prompts. Otherwise use the values sent as arguments or defaults.	
if [[ $userClicked == "Custom" ]]; then
	recordActivity "The user decided to provide custom names."
	
	FOLDERS[0]=$(/usr/bin/osascript -e 'text returned of (display dialog "Enter the name of folder 1" default answer "Utilities" buttons {"OK"} default button 1 with title "Folder that will hold the utilities" with icon POSIX file "/Users/Shared/Finder.icns")')
	
	FOLDERS[1]=$(/usr/bin/osascript -e 'text returned of (display dialog "Enter the name of folder 2" default answer "Tools" buttons {"OK"} default button 1 with title "Folder that will hold the tools" with icon POSIX file "/Users/Shared/Finder.icns")')
	
	FOLDERS[2]=$(/usr/bin/osascript -e 'text returned of (display dialog "Enter the name of folder 3" default answer "Help" buttons {"OK"} default button 1 with title "Folder that will hold the support documents" with icon POSIX file "/Users/Shared/Finder.icns")')
		
	recordActivity "User provided: ${FOLDER[@]}"
else
	recordActivity "User decided to use default values: ${FOLDER[@]}"
fi

#5. Go to the home folder.
cd $HOME

#6. Check to see if each of the folders exists. If it exists then do not create it. Else create the folder. 
recordActivity "Creating folders: ${FOLDER[@]}"

for item in ${FOLDER[@]}; do
	if [[ -d $item ]]; then
		recordActivity "Not creating $item as it already exists."
	else
		recordActivity "Creating $item"
		mkdir $item
	fi
	
	#7. Create the task completion file inside each folder.
	recordActivity "Creating hidden file for $item folder."
	cd $item
	#8. Generate the file names based on the folder names.
	touch ".$item-FolderCreated"
	cd ..
done

echo "$(date) Task completed. Have a nice day!"
	
#-------------------------------------------------------------------------------------------------
#-------------------------------------------------------------------------------------------------
#-------------------------------------------------------------------------------------------------
# ------------------------------ END OF SCRIPT ---------------------------------------------------

Summary

Both arrays and dictionaries now allow us to store collections of data in a single variable. This enables us to write compact scripts and deal with complex data.

Download

You can download the completed script from here.

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2 thoughts on “Shell scripting in macOS – Part 8: Arrays & Dictionaries”

  1. Pingback: Shell scripting in macOS – Part 1 | Arun Patwardhan's Blog

  2. Pingback: Shell scripting in macOS – Part 9: Automating scripts | Arun Patwardhan's Blog

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