== 'Argument list too long' is a misleading message

If you try to run a command with too many command line arguments, you
get an 'Argument list too long' error (technically you get an _E2BIG_
error from the kernel, which is then mapped into this error string by
your shell). There's a bunch of workarounds for this problem, such as
using _xargs_.

However, the error message is actually somewhat misleading. As old
Unix hands know (and new ones generally don't), the kernel's size
limit on _exec()_ is on ~~the combination of arguments and environment
variables~~. If you accidentally wind up with a huge environment and try
to start a program with even a few arguments, you'll fall over. (And if the
environment is big enough, you can't start any programs at all.)

Modern shells make this a more mysterious failure since they have so
many built in commands, which means that you can get a substantial way
into a shell script before you try to run an external command and fail.
The net result is that you can spend a bunch of time scratching your
head and trying to figure out why an innocent command with only a couple
of arguments is getting this error.

(If you need to figure out what the big environment variables are in the
Bourne shell, it is useful to know that the _export_ command without
any arguments lists all the environment variables, and it is a built-in
command so you can still use it in this situation. If you are trying to
use _tcsh_, you're on your own.)

=== Sidebar: why I'm so aware of this issue

Most people run into this issue only very rarely, because you need both
a very large shell variable or three *and* to have them exported to the
environment. Just pulling an unexpectedly large amount of data into a
variable to process it won't hit this. However, I use a shell that
automatically exports all shell variables into the environment, so
any time I pull a big value into a shell variable I run into this.

My workaround is simple; when I run external commands I null the variable
for the command, like so:

>  BIGVAR='' command ...

This is normally used to add some environment variables just for a
command, but it works fine to take them away too.

(This also works in the Bourne shell, although you are much less likely
to need it.)