Dumbing Down scp

The tool scp, UNIX for secure copy, is a wrapper around ssh, secure shell. It lets you move files from one machine to another through an encrypted connection with a command line syntax similar to that of the standard cp, local copy, command. I use it 100 times a day.

The command line syntax for scp is at its most basic:

scp <source> <destination>

Either the source, destination, or both can be on a remote computer. To denote that one just prefixes the file name with "username@machinename:". So this command:

scp myfile ry4an@elsewhere:/home/ry4an/myfile

would copy the contents of the local file named 'myfile' to a remote system named 'elsewhere' and place it in the directory /home/ry4an with the name myfile.

As a shortcut one can omit the destination directory and filename, in which case they default to the home directory of the specified user and the same filename as the original. Nice, simple, handy, straightforward.

However, when you're an idiot in a rush like me in addition to skipping the destination directory and filename you also skip the colon, yielding a command like:

scp myfile ry4an@elsewhere

When you make that mistake scp decides that what you wanted to do was take the local file named 'myfile' and copy it to another local file named 'ry4an@elsewhere'. That's certainly consistent with their syntax -- no colon, no remote system, but it is never what I want.

Instead I go to the 'elsewhere' machine and start looking for 'myfile' and it's not there, and I'm very puzzled because scp didn't give me any error messages. I don't know of anyone who has ever wanted scp to do a local copy, but for some reason the scp developers took extra time to add that feature. I want to remove it.

The best way would be to edit the scp source and neuter the part that does local copies. The problem with that is I'd have to modify the scp program on lots of machines, many of which I have no control over.

So, as a cheesy work around I spent a few seconds writing a bash shell function that refuses to invoke scp if there is no colon in the command line. It's a crappy band-aid on what's definitely a user-error problem, but it's already saved me from making the same frustrating mistake 10 times since I wrote it last week. Here it is in case anyone else has the same un-problem I do:

function scp () { if echo $* | grep -v -q -s : ; then
  echo scp: missing colon /usr/bin/scp
  /usr/bin/scp $@

Just put that in your .bashrc and forever be saved from having a drive full of user@elsewhere files. Or don't; I don't care about you.