How to create custom commands in Unix/Linux? [closed]

1. Create a directory say "bin" under your home directory.

2. Update your path variable to include this bin directory. Put this in .profile or .bash_profle file to make it permanent.

   export PATH=$PATH":$HOME/bin"

3. Create a script say, "hello" and keep it in your bin directory. Give execute permission to the hello script.

   #!/bin/bash    
   echo My first program

4. From any directory, you simply type:

   $ hello
   My first program

Easy, create an alias.

Say you want to write a command to cd into your download directory. And you want to call it cdd.

alias cdd='cd ~/Downloads' 

You can create any command you want.

Here is further information:
http://www.mediacollege.com/linux/command/alias.html

Most, if not all by now, Linux distributions have a little script in ~/.bashrc that looks almost identical to this:

if [ -e ~/.bash_aliases ]
then
. ~/.bash_aliases
fi

This merely means you can create your own commands (also known as 'aliases' usually referred to an existing command with some arguments you always have to use, or a list of commands that have to be executed in order).

Your Linux distribution will most likely not have the .bash_aliases file created in your home, unless you've manually done that already. So to create the file, type in the following command: touch ~/.bash_alisaes

Now that file will be executed automatically every time you fire off a new Terminal.

What you can do now is create a list of aliases and add them to that file for later uses. For example, the rm (remove) command by default does NOT ask you to confirm your request when you tell it to delete a file/directory. However, there is an argument that tells rm to ask you to confirm your request, -i. So, rm -i filePath will display a message asking you if you were sure you want to delete the specified file. Now, if you were to accidentally delete a file, you will very likely forget to include the -i option, and that's where an alias becomes very beneficial. Typing the following command

echo "alias rm='\rm -i'" >> ~/.bash_aliases

will tell Bash that every time you request to delete a file, a confirming message will be displayed to you. Of course, there is a lot more you can do, but this is just the basics.

Afterall, if you feel like wanting to learn how to use some basic command (i.e. cd, touch, rm, mkdir, pushd, popd, etc.) and/or more sophisticated ones, I'd recommend a very good book you can have on your bookshelf as a reference called

a practical guide to linux commands editors and shell programming, by Mark G. Sobell. ISBN: 978-0133085044