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Five Things You Must Consider Before ‘Developing an App’

By on 10 Mayıs 2020 in GNU/Linux İpuçları

Before you begin developing an app, it is worth taking the time to properly plan out your development cycle. From defining your intended feature set to load testing, the more work you do before you start coding, the quicker you will be able to progress through the actual development of your app.Below are five essential things to consider before developing your app. The more detailed your initial plans for your app, the smoother the entire development process will go. Before you even think about how to actually code your app, you need to establish exactly what it is going to do and why it is going to be doing it. If you want to develop an app just for the sake of it, this is a great way to teach yourself new skills. But if you are looking at developing an app with an eye to commercializing it, you need to know exactly what you are doing before you begin.

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The Purpose Of Your App

When developing an app for your business, there should be a clear rationale for you doing so. If you are only developing an app because you feel like you are supposed to or because your competitors have beaten you to the punch, the result is almost definitely going to be underwhelming.

On the other hand, if you take the time beforehand to plan your app properly and seriously consider how you can provide real value to your users, you stand a much better chance of critical and commercial success.

Before you can make any detailed plans about what your app will look like and what it will do, you need to be clear with yourself about what its main purpose is.

The Intended Feature Set

Once you have defined the ultimate purpose of your app, you can then begin to think about what features you need to include to achieve it.

Laying out your feature set should be one of the first things you do when you are preparing to develop an app. The features you want to include will have an impact on every other part of the design process.

For example, when it comes to your user interface, you will want to choose something that makes it easy for a user to see and access all of the features your app offers.

Equally, when you are assigning coders to various tasks, knowing what features you are shooting for will enable you to delegate work appropriately. There is no sense in asking a coder to work on a feature that lies well outside of their skill set.

The Price Point

If you are developing an app for a business, most of the time it will be distributed for free. It is important to know upfront whether the app you are working on is going to be provided for free, whether it will cost money, or whether there is an associated subscription cost as the buyer want to save money in all cases.

The price point at which you intend to sell an app will determine how much money you can sink into its development. It will also have a significant impact on the way that the app is marketed.

Fortunately, it is possible for you to have the best of all worlds when it comes to pricing. Many app developers have realized the potential in offering a free version of the app that is funded through advertising alongside a premium version that includes no ads.

The Platform

Before you can properly plan out your app development, you need to establish exactly what platform you are going to be aiming for.

Even if you intend to make your app available on every mobile operating system possible, you will still need to prioritize. In the vast majority of cases, it will make more sense to build your app for one primary platform first and then go about converting it for other platforms.

If you are trying to develop an app for multiple different platforms simultaneously, you are much more likely to run into problems.

Not only this, but you will find yourself having to solve problems for multiple different platforms at once. It is far more efficient to develop for your primary platform and iron out all the kinks before moving on to the next one.

App Load Testing

Developing an app is much more involved than many people realize. Lots of people think that once you have written the code and compiled the binary, your app is done and dusted. On the contrary, it doesn’t matter how talented your coders are or how much regression testing you have undertaken, there is still a range of things that you need to test under specific circumstances.

Load testing is one of many tests that can be used to assess an app’s performance under certain circumstances. Specifically, load testing will tell you how well your app performs when the system running it is under a heavy load and most of its available resources are being used.

For an app that is entirely offline, it is the system resources of the device it is running on that matter.

However, if your app also has online features, the current load placed on your internet connection will also be a factor in determining performance. In this case, many developers use proxies to load test their servers. Some proxy providers offer easy to use options.

Planning is everything in app development. If you take the time beforehand to work out exactly what you are doing and why then you will find the whole process much easier.

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Bash Scripting Part6 – Create and Use Bash Functions

By on 26 Ağustos 2019 in GNU/Linux İpuçları

Before we talk about bash functions, let’s discuss this situation. When writing bash scripts, you’ll find yourself that you are using the same code in multiple places. If you get tired of writing the same lines of code again and again in your bash script, it would be nice to write the block of code once and call it anywhere in your bash script. The bash shell allows you to do just that with Functions. Bash functions are blocks of code that you can reuse them anywhere in your code. Anytime you want to use this block of code in your script, you simply type the function name given to it. We are going to talk about how to create your own bash functions and how to use them in shell scripts.

Continue Reading →

Creating a function

You can define a function like this:

functionName() {

}

The brackets () is required to define the function.

Also, you can define the function using the function keyword, but this keyword is deprecated for POSIX portability.

function functionName() {

# Deprecated definition but still used and working

}

In the second definition, the brackets are not required.

Using Functions

#!/bin/bash

myfunc() {

echo "Using functions"

}

total=1

while [ $total -le 3 ]; do

myfunc

total=$(($total + 1))

done

echo "Loop finished"

myfunc

echo "End of the script"

Here we’ve created a function called myfunc and in order to call it, we just typed its name.

bash functions

The function can be called many times as you want.

Notice: If you try to use a function which is not defined, what will happen?

#!/bin/bash

total=1

while [ $total -le 3 ]; do

myfunc

total=$(($total + 1))

done

echo "Loop End"

myfunc() {

echo "Using function ..."

}

echo "End of the script"

call before declare

Oh, it’s an error because there no such function.

Another notice: bash function name must be unique. Otherwise, the new function will cancel the old function without any errors.

#!/bin/bash

myfunc() {

echo "The first function definition"

}

myfunc

function myfunc() {

echo "The second function definition"

}

myfunc

echo "End of the script"

override definition

As you can see, the second function definition takes control from the first one without any error so take care when defining functions.

Using the return Command

The return command returns an integer from the function.

There are two ways of using the return command; the first way is like this:

#!/bin/bash

myfunc() {

read -p "Enter a value: " value

echo "adding value"

return $(($value + 10))

}

myfunc

echo "The new value is $?"

return command

The myfunc function adds 10 to the  $value variable then show the sum using the $? Variable.

Don’t execute any commands before getting the value of the function, because the variable $? returns the status of the last line.

This return method returns integers. what about returning strings?

Using Function Output

The second way of returning a value from a bash function is command substitution. This way, you can return anything from the function.

#!/bin/bash

myfunc() {

read -p "Enter a value: " value

echo $(($value + 10))

}

result=$(myfunc)

echo "The value is $result"

bash functions output

Passing Parameters

We can deal with bash functions like small snippets that can be reused and that’s OK, but we need to make the function like an engine, we give it something and it returns a result based on what we provide.

You can use the environment variables to process the passed parameters to the function. The function name is declared as $0 variable, and the passed parameters are $1, $2, $3, etc.

You can get the number of passed parameters to the function using the ($#) variable.

We pass parameters like this:

myfunc $val1 10 20

The following example shows how to use the ($#) variable:

#!/bin/bash

addnum() {

if [ $# -gt 2 ]; then

echo "Incorrect parameters passed" # If parameters no equal 2

else

echo $(($1 + $2)) # Otherwise add them

fi

}

echo -n "Adding 10 and 15: "

value=$(addnum 10 15)

echo $value

echo -n "Adding three numbers: "

value=$(addnum 10 15 20)

echo $value

pass parameters

The addnum function gets the passed parameters count. If greater than 2 passed, it returns -1.

If there’s one parameter, the addnum function adds this parameter twice. If 2 parameters passed, the addnum function adds them together, and if you try to add three parameters it will return -1.

If you try to use the passed parameters inside the function, it fails:

#!/bin/bash

myfunc() {

echo $(($1 + $2 + $3 + $4))

}

if [ $# -eq 4 ]; then

value=$(myfunc)

echo "Total= $value"

else

echo "Passed parameters like this: myfunc a b c d"

fi

unknown parameters

Instead, you have to send them to the function like this:

#!/bin/bash

myfunc() {

echo $(($1 + $2 + $3 + $4))

}

if [ $# -eq 4 ]; then

value=$(myfunc $1 $2 $3 $4)

echo "Total= $value"

else

echo "Passed parameters like this: myfunc a b c d"

fi

bash functions parameters

Now it works!!

Processing Variables in Bash Functions

Every variable we use has a scope, the scope is variable visibility to your script.

You can define two types of variables:

  • Global
  • Local

Global Variables

They are visible and valid anywhere in the bash script. You can even get its value from inside the function.

If you declare a global variable within a function, you can get its value from outside the function.

Any variable you declare is a global variable by default. If you define a variable outside the function, you call it inside the function without problems:

#!/bin/bash

myfunc() {

input=$(($input + 10))

}

read -p "Enter a number: " input

myfunc

echo "The new value is: $input"

global variables

If you change the variable value inside the function, the value will be changed outside of the function.

So how to overcome something like this? Use local variables.

Local Variables

If you will use the variable inside the function only, you can declare it as a local variable using the local keyword  like this:

local tmp=$(( $val + 10 ))

So if you have two variables, one inside the function and the other is outside the function and they have the identical name, they won’t affect each other.

#!/bin/bash

myfunc() {

local tmp=$(($val + 10))

echo "The Temp from inside function is $tmp"

}

tmp=4

myfunc

echo "The temp from outside is $tmp"

local variables

When you use the $tmp variable inside the myfunc function, it doesn’t change the value of the $tmp which is outside the function.

Passing Arrays As Parameters

What will happen if you pass an array as a parameter to a function:

#!/bin/bash

myfunc() {

echo "The parameters are: $@"

arr=$1

echo "The received array is ${arr[*]}"

}

my_arr=(5 10 15)

echo "The old array is: ${my_arr[*]}"

myfunc ${my_arr[*]}

pass arrays

The function only takes the first value of the array variable.

You should disassemble the array into its single values, then use these values as function parameters. Finally, pack them into an array in the function like this:

#!/bin/bash

myfunc() {

local new_arr

new_arr=("$@")

echo "Updated value is: ${new_arr[*]}"

}

my_arr=(4 5 6)

echo "Old array is ${my_arr[*]}"

myfunc ${my_arr[*]}

pass arrays solution

The array variable was rebuilt thanks to the function.

Recursive Function

This feature enables the function to call itself from within the function itself.

The classic example of a recursive function is calculating factorials. To calculate the factorial of 3, use the following equation:

3! = 1 * 2 * 3

Instead, we can use the recursive function like this:

x! = x * (x-1)!

So to write the factorial function using bash scripting, it will be like this:

#!/bin/bash

fac_func() {

if [ $1 -eq 1 ]; then

echo 1

else

local tmp=$(($1 - 1))

local res=$(fac_func $tmp)

echo $(($res * $1))

fi

}

read -p "Enter value: " val

res=$(fac_func $val)

echo "The factorial of $val is: $res"

bash recursive function

Using recursive bash functions is so easy!

Creating Libraries

Now we know how to write functions and how to call them, but what if you want to use these bash functions or blocks of code on different bash script files without copying and pasting it on your files.

You can create a library for your functions and point to that library from any file as you need.

By using the source command, you can embed the library file script inside your shell script.

The source command has an alias which is the dot. To source a file in a shell script, write the following line:

. ./myscript

Let’s assume that we have a file called myfuncs that contains the following:

addnum() {

echo $(($1 + $2 + $3 + $4))

}

Now, we will use it in another bash script file like this:

#!/bin/bash

. ./myfuncs

result=$(addnum 10 10 5 5)

echo "Total = $result"

source command

Awesome!! We’ve used the bash functions inside our bash script file, we can also use them in our shell directly.

Use Bash Functions From Command Line

Well, that is easy, if you read the previous post which was about the signals and jobs you will have an idea about how to source our functions file in the bashrc file and hence we can use the functions directly from the bash shell. Cool

Edit the bashrc file at /home/username and add this line:

. /home/likegeeks/Desktop/myfuncs

Make sure you type the correct path.

Now the function is available for us to use in the command line directly:

addnum 10 20

use from shell

Note: you may need to log out and log in to use the bash functions from the shell.

Another note: if you make your function name like any of the built-in commands you will overwrite the default command so you should take care of that.

I hope you like the post. Keep coming back.

Thank you.

0

Bash Scripting Part6 – Create and Use Bash Functions

By on 10 Aralık 2017 in GNU/Linux İpuçları

Before we talk about bash functions, let’s discuss this situation. When writing bash scripts, you’ll find yourself that you are using the same code in multiple places. If you get tired of writing the same lines of code again and again in your bash script, it would be nice to write the block of code once and call it anywhere in your bash script. The bash shell allows you to do just that with Functions. Bash functions are blocks of code that you can reuse them anywhere in your code. Anytime you want to use this block of code in your script, you simply type the function name given to it. We are going to talk about how to create your own bash functions and how to use them in shell scripts.

Continue Reading →

Creating a function

You can create a function like this:

functionName {

}

Or like this:

functionName() {

}

The parenthesis on the second snippet is used to pass values to the function from outside of it, so these values can be used inside the function.

Using Functions

#!/bin/bash

function myfunc {

echo "Using functions"

}

total=1

while [ $total -le 3 ]

do

myfunc

total=$(( $total + 1 ))

done

echo "Loop finished"

myfunc

echo "End of the script"

Here we’ve created a function called myfunc and in order to call it, we just typed its name.

bash functions

The function can be called many times as you want.

Notice: If you try to use a function which is not defined, what will happen?

#!/bin/bash

total=1

while [ $total -le 3 ]

do

myfunc

total=$(( $total + 1 ))

done

echo "Loop End"

function myfunc {

echo "Using function ..."

}

echo "End of the script"

bash functions call before declare

Oh, it’s an error because there no such function.

Another notice: bash function name must be unique. Otherwise, the new function will cancel the old function without any errors.

#!/bin/bash

function myfunc {

echo "The first function definition"

}

myfunc

function myfunc {

echo "The second function definition"

}

myfunc

echo "End of the script"

bash functions override definition

As you can see, the second function definition takes control from the first one without any error so take care when defining functions.

Using the return Command

The return command returns an integer from the function.

There are two ways of using return command; the first way is like this:

#!/bin/bash

function myfunc {

read -p "Enter a value: " value

echo "adding value"

return $(( $value + 10 ))

}

myfunc

echo "The new value is $?"

bash functions return command

The myfunc function adds 10 to the  $value variable then show the sum using the $? Variable.

Don’t execute any commands before getting the value of the function, because the variable $? returns the status of the last line.

This return method returns integers. what about returning strings?

Using Function Output

The second way of returning a value from a bash function is command substitution. This way, you can return anything from the function.

#!/bin/bash

function myfunc {

read -p "Enter a value: " value

echo $(( $value + 10 ))

}

result=$( myfunc)

echo "The value is $result"

bash functions output

Passing Parameters

We can deal with bash functions like small snippets that can be reused and that’s OK, but we need to make the function like an engine, we give it something and it returns a result based on what we provide.

You can use the environment variables to process the passed parameters to the function. The function name is declared as $0 variable, and the passed parameters are $1, $2, $3, etc.

You can get the number of passed parameters to the function using the ($#) variable.

We pass parameters like this:

myfunc $val1 10 20

The following example shows how to use the ($#) variable:

#!/bin/bash

function addnum {

if [ $# -gt 2 ]

then

# If parameters no equal 2

echo "Incorrect parameters passed"

else

# Otherwise add them

echo $(( $1 + $2 ))

fi

}

echo -n "Adding 10 and 15: "

value=$(addnum 10 15)

echo $value

echo -n "Adding three numbers: "

value=$(addnum 10 15 20)

echo $value

bash functions pass parameters

The addnum function gets the passed parameters count. If greater than 2 passed, it returns -1.

If there’s one parameter, the addnum function adds this parameter twice. If 2 parameters passed, the addnum function adds them together, and if you try to add three parameters it will return -1.

If you try to use the passed parameters inside the function, it fails:

#!/bin/bash

function myfunc {

echo $(( $1 + $2 + $3 + $4))

}

if [ $# -eq 4 ]

then

value=$( myfunc)

echo "Total= $value"

else

echo "Passed parameters like this: myfunc a b c d"

fi

bash functions unknown parameters

Instead, you have to send them to the function like this:

#!/bin/bash

function myfunc {

echo $(( $1 + $2 + $3 + $4))

}

if [ $# -eq 4 ]

then

value=$(myfunc $1 $2 $3 $4)

echo "Total= $value"

else

echo "Passed parameters like this: myfunc a b c d"

fi

bash functions parameters

Now it works!!

Processing Variables in Bash Functions

Every variable we use has a scope, the scope is variable visibility to your script.

You can define two types of variables:

  • Global
  • Local

Global Variables

They are visible and valid anywhere in the bash script. You can even get its value from inside the function.

If you declare a global variable within a function, you can get its value from outside the function.

Any variable you declare is a global variable by default. If you define a variable outside the function, you call it inside the function without problems:

#!/bin/bash

function myfunc {

input=$(( $input + 10 ))

}

read -p "Enter a number: " input

myfunc

echo "The new value is: $input"

bash functions global variables

If you change the variable value inside the function, the value will be changed outside of the function.

So how to overcome something like this? Use local variables.

Local Variables

If you will use the variable inside the function only, you can declare it as a local variable using the local keyword  like this:

local tmp=$(( $val + 10 ))

So if you have two variables, one inside the function and the other is outside the function and they have the identical name, they won’t affect each other.

#!/bin/bash

function myfunc {

local tmp=$[ $val + 10 ]

echo "The Temp from inside function is $tmp"

}

tmp=4

myfunc

echo "The temp from outside is $tmp"

bash functions local variables

When you use the $tmp variable inside the myfunc function, it doesn’t change the value of the $tmp which is outside the function.

Passing Arrays As Parameters

What will happen if you pass an array as a parameter to a function:

#!/bin/bash

function myfunc {

echo "The parameters are: $@"

arr=$1

echo "The received array is ${arr[*]}"

}

my_arr=(5 10 15)

echo "The old array is: ${my_arr[*]}"

myfunc $my_arr

bash functions pass arrays

The function only takes the first value of the array variable.

You should disassemble the array into its single values, then use these values as function parameters. Finally, pack them into an array in the function like this:

#!/bin/bash

function myfunc {

local new_arr

new_arr=("$@")

echo "Updated value is: ${new_arr[*]}"

}

my_arr=(4 5 6)

echo "Old array is ${my_arr[*]}"

myfunc ${my_arr[*]}

bash functions pass arrays solution

The array variable was rebuilt thanks to the function.

Recursive Function

This feature enables the function to call itself from within the function itself.

The classic example of a recursive function is calculating factorials. To calculate the factorial of 3, use the following equation:

3! = 1 * 2 * 3

Instead, we can use the recursive function like this:

x! = x * (x-1)!

So to write the factorial function using bash scripting, it will be like this:

#!/bin/bash

function fac_func {

if [ $1 -eq 1 ]

then

echo 1

else

local tmp=$(( $1 - 1 ))

local res=$(fac_func $tmp)

echo $(( $res * $1 ))

fi

}

read -p "Enter value: " val

res=$(fac_func $val)

echo "The factorial of $val is: $res"

bash recursive function

Using recursive bash functions is so easy!

Creating Libraries

Now we know how to write functions and how to call them, but what if you want to use these bash functions or blocks of code on different bash script files without copying and pasting it on your files.

You can create a library for your functions and point to that library from any file as you need.

By using the source command, you can embed the library file script inside your shell script.

The source command has an alias which is the dot. To source a file in a shell script, write the following line:

. ./myscript

Let’s assume that we have a file called myfuncs that contains the following:

function addnum {

echo $(( $1 + $2 + $3 + $4))

}

Now, we will use it in another bash script file like this:

#!/bin/bash

. ./myfuncs

result=$(addnum 10 10 5 5)

echo "Total = $result"

bash functions source command

Awesome!! We’ve used the bash functions inside our bash script file, we can also use them in our shell directly.

Use Bash Functions From Command Line

Well, that is easy, if you read the previous post which was about the signals and jobs you will have an idea about how to source our functions file in the .bashrc file and hence we can use the functions directly from the bash shell. Cool

Edit the .bashrc file and add this line:

. /home/likegeeks/Desktop/myfuncs

Make sure you type the correct path.

Now the function is available for us to use in the command line directly:

$ addnum 10 20

bash functions use from shell

Note: you may need to logout and login to use the bash functions from the shell.

Another note: if you make your function name like any of the built-in commands you will overwrite the default command so you should take care of that.

I hope you like the post. Keep coming back.

Thank you.

likegeeks.com

0