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