What is the use of "set -u" in .profile?

[Gulam Mohiuddin]

What is the use of "set -u" parameter in the .profile login file.

Thanks.

[Chris Wilshaw]

from the sh-posix man page;

-u Treat unset parameters as an error when substituting.

[Jeff Schussele]

Hi,

From the ksh & sh-posix man page:

-u Treat unset parameters as an error when substituting

Which means I believe that during a command substitution - EX $(command) - that any parameters that may be necessary that are unset will result in an error & not defaulted.

Rgds,
Jeff

[Todd McDaniel_1 · Accepted solution]

In this case "set" is not associated with an editor like EX or VI... but a command line method to either assign a env variables or set env parms...

If you have any named $VAR and they are not defined (ie have no value) they will cause an error message when your .profile is executed as you login.

A $VAR cannot have a null value for your env when invoking your .profile

This is why sometimes you will see an error for "TERM not set" when you login

[Bill Hassell]

The definitions given are correct, but why would you want to use it? From a painful experience where a spelling error deleted /usr/local/bin from 200+ machines, I ALWAYS write scripts with set -u. The shell's default behavior is to treat undefined variables as being set to null. So if you had a script like this:

for MYNAME in $LIST_OF_FILES
do
rm -rf /usr/local/bin/$MYNAM
done

If set -u was executed prior to this code, it will stop before running the rm command because $MYNAME is not = $MYNAM and therefore, $MYNAM is undefined (actually misspelled but still undefined). If set +u is in force (the default) then the script would run:

rm -rf /usr/local/bin/

and the entire directory, all files and subdirectories, would be removed (that's a bad thing!). So to prevent these mistakes, use set -u.

[Jeroen Peereboom]

Bill is right: it's good programming practice to have a set -u.

I wonder however what happens if you login with CDE. and .dtprofile sources .profile and an error occurs. Are you logged in or thrown out?

JP