path: root/doc/pkgMkIndex.n

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'\" Copyright (c) 1996 Sun Microsystems, Inc.
'\"
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'\" SCCS: @(#) pkgMkIndex.n 1.8 97/10/31 12:51:13
'\" 
.so man.macros
.TH pkg_mkIndex n 7.6 Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
pkg_mkIndex \- Build an index for automatic loading of packages
.SH SYNOPSIS
.nf
\fBpkg_mkIndex \fIdir\fR \fIpattern \fR?\fIpattern pattern ...\fR?
.fi
.BE

.SH DESCRIPTION
.PP
\fBPkg_mkIndex\fR is a utility procedure that is part of the standard
Tcl library.
It is used to create index files that allow packages to be loaded
automatically when \fBpackage require\fR commands are executed.
To use \fBpkg_mkIndex\fR, follow these steps:
.IP [1]
Create the package(s).
Each package may consist of one or more Tcl script files or binary files.
Binary files must be suitable for loading with the \fBload\fR command
with a single argument;  for example, if the file is \fBtest.so\fR it must
be possible to load this file with the command \fBload test.so\fR.
Each script file must contain a \fBpackage provide\fR command to declare
the package and version number, and each binary file must contain
a call to \fBTcl_PkgProvide\fR.
.IP [2]
Create the index by invoking \fBpkg_mkIndex\fR.
The \fIdir\fR argument gives the name of a directory and each
\fIpattern\fR argument is a \fBglob\fR-style pattern that selects
script or binary files in \fIdir\fR.
\fBPkg_mkIndex\fR will create a file \fBpkgIndex.tcl\fR in \fIdir\fR
with package information about all the files given by the \fIpattern\fR
arguments.
It does this by loading each file and seeing what packages
and new commands appear (this is why it is essential to have
\fBpackage provide\fR commands or \fBTcl_PkgProvide\fR calls
in the files, as described above).
.VS "" br
.IP [3]
Install the package as a subdirectory of one of the directories given by
the \fBtcl_pkgPath\fR variable.  If \fB$tcl_pkgPath\fR contains more
than one directory, machine-dependent packages (e.g., those that
contain binary shared libraries) should normally be installed
under the first directory and machine-independent packages (e.g.,
those that contain only Tcl scripts) should be installed under the
second directory.
The subdirectory should include
the package's script and/or binary files as well as the \fBpkgIndex.tcl\fR
file.  As long as the package is installed as a subdirectory of a
directory in \fB$tcl_pkgPath\fR it will automatically be found during
\fBpackage require\fR commands.
.RS
.LP
If you install the package anywhere else, then you must ensure that
the directory contaiingn the package is in the \fBauto_path\fR global variable
or an immediate subdirectory of one of the directories in \fBauto_path\fR.
\fBAuto_path\fR contains a list of directories that are searched
by both the auto-loader and the package loader; by default it
includes \fB$tcl_pkgPath\fR.
The package loader also checks all of the subdirectories of the
directories in \fBauto_path\fR.
.VE
You can add a directory to \fBauto_path\fR explicitly in your
application, or you can add the directory to your \fBTCLLIBPATH\fR
environment variable:  if this environment variable is present,
Tcl initializes \fBauto_path\fR from it during application startup.
.RE
.IP [4]
Once the above steps have been taken, all you need to do to use a
package is to invoke \fBpackage require\fR.
For example, if versions 2.1, 2.3, and 3.1 of package \fBTest\fR
have been indexed by \fBpkg_mkIndex\fR, the command
\fBpackage require Test\fR will make version 3.1 available
and the command \fBpackage require \-exact Test 2.1\fR will
make version 2.1 available.
There may be many versions of a package in the various index files
in \fBauto_path\fR, but only one will actually be loaded in a given
interpreter, based on the first call to \fBpackage require\fR.
Different versions of a package may be loaded in different
interpreters.

.SH "PACKAGES AND THE AUTO-LOADER"
.PP
The package management facilities overlap somewhat with the auto-loader,
in that both arrange for files to be loaded on-demand.
However, package management is a higher-level mechanism that uses
the auto-loader for the last step in the loading process.
It is generally better to index a package with \fBpkg_mkIndex\fR
rather than \fBauto_mkindex\fR because the package mechanism provides
version control:  several versions of a package can be made available
in the index files, with different applications using different
versions based on \fBpackage require\fR commands.
In contrast, \fBauto_mkindex\fR does not understand versions so
it can only handle a single version of each package. 
It is probably not a good idea to index a given package with both
\fBpkg_mkIndex\fR and \fBauto_mkindex\fR.
If you use \fBpkg_mkIndex\fR to index a package, its commands cannot
be invoked until \fBpackage require\fR has been used to select a
version;  in contrast, packages indexed with \fBauto_mkindex\fR
can be used immediately since there is no version control.

.SH "HOW IT WORKS"
.PP
\fBPkg_mkIndex\fR depends on the \fBpackage unknown\fR command,
the \fBpackage ifneeded\fR command, and the auto-loader.
The first time a \fBpackage require\fR command is invoked,
the \fBpackage unknown\fR script is invoked.
This is set by Tcl initialization to a script that
evaluates all of the \fBpkgIndex.tcl\fR files in the
\fBauto_path\fR.
The \fBpkgIndex.tcl\fR files contain \fBpackage ifneeded\fR
commands for each version of each available package;  these commands
invoke \fBpackage provide\fR commands to announce the
availability of the package, and they setup auto-loader
information to load the files of the package.
A given file of a given version of a given package isn't
actually loaded until the first time one of its commands
is invoked.
Thus, after invoking \fBpackage require\fR you won't see
the package's commands in the interpreter, but you will be able
to invoke the commands and they will be auto-loaded.

.SH KEYWORDS
auto-load, index, package, version