How to change the PATH

Motivation:

You plan to make your own programs.
You will put them in some directory.
Normal choice is put them in $HOME/bin
This directory must be in PATH

To put $HOME/bin in PATH, put this line:

   export PATH=$PATH:$HOME/bin

in this file:

   $HOME/.profile

To test it:

  source $HOME/.profile
  echo $PATH

Or just logout and login again.

Notes

You could also put the line here:
```
   $HOME/.bashrc 
```
See discussion of Linux/Unix configuration files.
You can add more directories to PATH, separated by ":"
You can add current directory "." to PATH.

OS programs and your programs

You type the names of OS programs and your programs.
So some issues arise:

Can your programs use the same name as OS programs?
If you add your dirs to PATH, should they be at start or end of PATH?

Discussion:

Type "which ls" to see location of the OS ls program.
If you write your own "ls" program, and insert it in a dir in the PATH which comes before the OS directory, then you have over-ridden the system ls. All calls to "ls" at the command-line will be calls to your program, not system ls.
This may be ok for you, but other programs that call ls will now be calling your version instead. They may fail in unexpected ways.

Recommended:

If you use your own directory ($HOME/bin) or the current directory (.) in the PATH, put them at end of PATH, not start.
Do not use OS command names. Do "which" before choosing a program name to make sure it does not exist.

Optional experiment: "." in the PATH can be security risk

This is an advanced optional experiment to show that "." in the PATH can be a security risk.
Only advanced users should attempt this.
Do the following experiment with a friend:

Put "." at the start of your PATH.
Get your friend to make their home directory "r-x" for group.
Get your friend to make a program called "ls" in their home directory. The program is:
```
echo "You have been hacked."
echo "I will now rm your files."
```
"cd" to your friend's home directory and type "ls"
Now you see the problem?
"cd" to my home directory, which is "--x" for you, and type "ls".
That is odd too. Why?

Cleanup:

Get your friend to set their home directory back to normal "---" for group.
Remove "." from your PATH or put it at the end.