Guide to build CLI with PHP [Hypertext Preprocessor]

What is CLI [Command line interface]?
- CLI is a command-line program that accepts text input to execute operating system functions.
Why to use PHP CLI?
- because there are several advantages in being able to run PHP code from the command line such as:
  - PHP into a general-purpose language to execute on any environment, not only on web servers.
  - no need to learn another language such as Perl, Bash, Awk or python
  - running scheduled (CRON) tasks.
  - making GUI applications with GTK.
  - reuse of your existing components.
  - write very robust scripts for your system using multi-threading capabilities.
  - access system STDIN [input], STDOUT [output], STERR [error].

Sample App

in this Guide, we will use vim editor and you are free to use vscode or anything you like
for php://stdin, php://stdout and php://stderr check Accessing various I/O streams

We need to create our executable file and protect it from running on the web servers.
1. vim [example] -> (filename) then press Enter [notes that we didn't add the extension for the file for protecting it].
2. make our file executable via our OS using the command chmod -x example.
Writing our program.
1. start your file with the following sentence.
  - if you are following this guide using vim press i so you can start typing.
  - #!/usr/bin/env php to make our code executable via PHP installed on our machine.
  - after making sure that our program can execute our PHP code then open your PHP tag and start to write your code.
2. Inputs
  - to read input while starting the CLI app use super global indexed array $_SERVER["argv"]
    - to access first input $_SERVER["argv"][0] the second - to access first input $_SERVER["argv"][1], etc
    - to get count of the parameter passed via starting the CLI app access it using $_SERVER["argc"]
  - after running the CLI app can make it reactive with the user which you are building the app for him use $input = fread(fopen('php://stdin','r'), $length);
    - $length -> length of bytes you want to read
3. Outputs
  - echo $output|| print($output)
  - fwrite(fopen('php://stdout','w'), $output)