'''package require''' ''?-'''''exact'''''? package ?version?''

This command is typically invoked by Tcl code that wishes to use a particular version of a particular package. The arguments indicate which package is wanted, and the command ensures that a suitable version of the package is loaded into the interpreter. If the command succeeds, it returns the version number that is loaded; otherwise it generates an error. If both the -'''exact''' switch and the ''version'' argument are specified then only the given version is acceptable. If -'''exact''' is omitted but ''version'' is specified, then versions later than ''version'' are also acceptable as long as they have the same major version number as ''version''. If both -'''exact''' and ''version'' are omitted then any version whatsoever is acceptable. If a version of ''package'' has already been provided (by invoking the '''[package provide]''' command), then its version number must satisfy the criteria given by -'''exact''' and ''version'' and the command returns immediately. Otherwise, the command searches the database
of information provided by previous '''[package ifneeded]''' commands to see if an acceptable version of the package is available. If so, the script for the highest acceptable version number is evaluated in the global namespace; it must do whatever is necessary to load the package, including calling '''[package provide]''' for the package. If the '''[package ifneeded]''' database does not contain an acceptable version of the package and a '''[package unknown]''' command has been specified for the interpreter then that command is evaluated in the global namespace; when it completes, Tcl checks again to see if the package is now provided or if there is a '''[package ifneeded]''' script for it. If all of these steps fail to provide an acceptable version of the package, then the command returns an error.

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See also:

   * [package]
   * [package ifneeded]
   * [package provide]
   * [package require]
   * [package unknown]

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''[escargo] 20 Nov 2003'' - Is there any easy way to tell ''where'' a package is loaded from?
am looking at code that does a '''package require snit 0.9''' and the value returned is '''0.82''',
and it is not at all obvious where that value is coming from.

'''[DGP]''' Use [package ifneeded] to discover what script
was used to load a package.

    package ifneeded snit [package require snit]

That will return the script that loaded snit, which
likely looks something like:

    source /absolute/path/to/snit/snit.tcl

Is that what you were asking?

'''[escargo]''' - Yes (modulo the correction of '''package provide''' to
'''package require''' in the snippet above).  I'm running some experimental
[Snit] code, which is at version 0.9; the version in tcllib1.5 is 0.82 which
seems to satisfy a '''package require snit 0.9'''.

'''[DGP]''' My original code assumed you already had
snit loaded in your interp.  In that case, [package provide]
(or even [package present]) is better than [package require].

And yes, 82 > 9, so 0.82 is a later release than 0.9.
Any package developer that means 0.8.2 should say so.

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But what about the developer who thought that 82 would be less than 90 ?

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