envpathp - Online in the Cloud

PROGRAM:

NAME

envpath - Advanced operations on path variables

SYNOPSIS

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

DESCRIPTION

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

SIMPLE MODE
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
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*.

CLEARCASE WINKINS

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.

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