I'm working on a makefile rule and wish to unset the environment variable MAKEFILES before invoking make again recursively. On other BSD systems, I do it like this:
env -u MAKEFLAGS $(MAKE) $(SUBDIR_ARGS)
On Linux, I do it like this:
env --unset=MAKEFLAGS $(MAKE) $(SUBDIR_ARGS)
However, neither style is working on Macintosh OS X Mavericks, although, I would expect the BSD style used elsewhere to work.
The error I get with the BSD style invocation is:
env: illegal option -- u
How can I unset an environment variable before invoking a command on OS X and why doesn't the BSD style used elsewhere work?
Here is Mac's man page for env:
ENV(1) BSD General Commands Manual ENV(1)
NAME
env -- set and print environment
SYNOPSIS
env [-i] [name=value ...] [utility [argument ...]]
DESCRIPTION
env executes utility after modifying the environment as specified on the command line. The option name=value specifies an environmental variable, name, with a value of value. The option `-i' causes env to completely ignore the environment it inherits.
If no utility is specified, env prints out the names and values of the variables in the environment, with one name=value pair per line.
DIAGNOSTICS
If the utility is invoked, the exit status of env shall be the exit status of utility; otherwise, the env utility exits with one of the following values:
0 The env utility completed successfully
1-125 An error occurred in the env utility.
126 The utility specified by utility was found, but could not be invoked.
127 The utility specified by utility could not be found.
COMPATIBILITY
The historic - option has been deprecated but is still supported in this implementation.
SEE ALSO
execvp(3), environ(7)
STANDARDS
The env utility conforms to IEEE Std 1003.2-1992 (``POSIX.2'').
BUGS
env doesn't handle commands with equal (``='') signs in their names, for obvious reasons.
BSD August 27, 1993 BSD
Use the unset
command. From the man pages:
unset
Remove variable or function names - the opposite of set.
Syntax
unset [-fv] [name ...]
Key
-v Each name refers to a shell variable.(default)
-f Each name refers to a shell function, and the function definition is removed.
Example
$ unset myvariable
Each unset variable or function is removed from the environment passed to subsequent commands. If any of RANDOM, SECONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are unset, they lose their special properties, even if they are subsequently reset.
The exit status is true unless a name is readonly. It is not an error for nothing to be unset.
unset is a bash built in command.
"Look Dave, I can see you're really upset about this" ~ HAL (Space 2001)