envpath(1) Advanced operations on path variables


Run this script with the "-help" option for usage details.


Parses the command line, modifies the specified path variable(s), and execs the remaining arguments. There are two modes, simple and advanced:


Simple mode presents an alternative, platform-independent syntax for specifying paths wherein the path separator is ``,'' and environment variables can be expanded with @NAME@. For example

    envpath PATH=@PATH@,/usr/ucb -- printenv PATH

appends "/usr/ucb" to $PATH and execs printenv PATH. The "--" is optional.

You can also specify prepending or appending by using "+=" or "=+" respectively:

    # place /usr/ucb at the front
    envpath PATH+=/usr/ucb -- printenv PATH
    # place /usr/ucb at the back
    envpath PATH=+/usr/ucb -- printenv PATH

Simple mode requires only this script; it does not require Env::Path to be installed.


Advanced mode basically provides command-line access to the features of Env::Path (see), which must be installed. The "-E" flag selects the path variable to operate on and other flags specify operations on it. E.g.

    envpath -E MANPATH -A /tmp -R /usr/share/man -N -U -- man ...

would take MANPATH, append /tmp to it, remove any references to "/usr/share/man", remove any dirs which don't exist ("-N") and remove redundant entries ("-U") before running man.

The -Whence option allows patterns. Thus

    envpath -W "cat*"

would find all programs on PATH which match cat*.


A big part of the motivation for this script was for use with ClearCase builds; iff you know or care about ClearCase read on. Typically, during builds (and not just with ClearCase), pathvars such as PATH, CLASSPATH, and LD_LIBRARY_PATH must be strictly controlled. One choice is to force static values of these into the environment during the build process, another is to simply require/expect users to set their paths appropriately. Each of these can lead to subtle build or runtime errors, however, and makes it hard for new users to get up to speed since their personal environment must be just so.

Another common choice is to use only full pathnames within the Makefile, avoiding reliance on search paths at all. This is often the best way to go but can suppress ClearCase winkins. For example, say you're generating ascii files of some type with a binary executable you just built:

$(INCDIR)/foo.h: $(BINDIR)/foomaker         $(BINDIR)/foomaker ...

The problem with this is that $(BINDIR) likely contains a platform part such as 'solaris' or 'hpux', which makes it impossible to wink in the foo.h file on other platforms even though it's ascii. This same thing could come up even with a standard pre-built utility that's in different places on different platforms; "yacc", for instance, is in /usr/bin on Linux and /usr/ccs/bin on Solaris.

You could modify the path on the fly:

$(INCDIR)/foo.h: $(BINDIR)/foomaker         PATH=$(BINDIR)$(SEP)$$PATH foomaker ...

but this suffers from the same problem: since $(BINDIR) and $PATH are expanded literally within the build script they'll suppress winkins. Here's a solution using envpath:

$(INCDIR)/foo.h: $(BINDIR)/foomaker         envpath PATH=@BINDIR@,@PATH@ foomaker ...

This hides the evaluation of BINDIR and PATH such that clearmake never sees anything but the literals, thus clearing the field for winkins. Of course envpath is capable of doing more than this, but it's the original reason it was written.


David Boyce <dsbperl AT boyski.com>


Copyright (c) 2000-2001 David Boyce. All rights reserved. This Perl program is free software; you may redistribute and/or modify it under the same terms as Perl itself.