[Chapter 10] 10.10 Simulated Bourne Shell Functions and Aliases
Author: Jerry Peek, Tim O'Reilly & Mike Loukides
Date: 1998-08-04T21:36:00Z

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| Chapter 10 Aliases |

## 10.10 Simulated Bourne Shell Functions and Aliases

If you have a Bourne shell with no functions (10.9) or aliases (10.2), you can do a lot of the same things with shell variables and the eval (8.10) command.

Let's look at an example. First, here's a shell function named scp (safe copy). If the destination file exists and isn't empty, the function prints an error message instead of copying:

    test
    scp()
    {
       if test ! -s "$2"
       then cp "$1" "$2"
       else echo "scp: cannot copy $1: $2 exists"
       fi
    }

If you use the same scp twice, the first time you'll make bfile. The second time you try, you see the error:

>     $ scp afile bfile
>        ...
>     $ scp afile bfile
>     scp: cannot copy afile: bfile exists

Here's the same scp-stored in a shell variable instead of a function:

>     scp='
>     if test ! -s "$2"
>     then cp "$1" "$2"

>     else echo "scp: cannot copy $1: $2 exists"
>     fi
>     '

Because this fake function uses shell parameters, you have to add an extra step: setting the parameters. Simpler functions are easier to use:

    set
    $ set afile bfile
    $ eval "$scp"
       ...
    $ eval "$scp"
    scp: cannot copy afile: bfile exists

- JP

10.9 Shell Functions |  | 11. The Lessons of History