String substitution using the r alias

You can use the r Korn shell alias to modify a command before it is run.

In this case, a substitution parameter of the form Old=new can be used to modify the command before it is run.

The following examples show how to use the r alias:

If command line 940 is ls *.txt, and you want to run ls *.exe, at the prompt, type the following:
```
r txt=exe 940
```
This runs command 940, substituting exe for txt.
If the command on line 940 is the most recent command that starts with a lowercase letter l, you can also type the following:
```
r txt=exe l
```

Note: Only the first occurrence of the Old string is replaced by the New string. Entering the r Korn shell alias without a specific command number or character performs the substitution on the immediately previous command entered.