Author:         Don Porter <[email protected]>
State:          Final
Type:           Project
Vote:           Done
Created:        17-Sep-2022
Tcl-Version:    9.0
Tcl-Branch:	novem
    Vote-Summary:   Accepted 6/0/0
    Votes-For:      DP, JN, SL, FV, KK, KW
    Votes-Against:  none
    Votes-Present:  none

Abstract

This TIP proposes revising the behavior of [glob] to return an empty list without error when no matches are found.

Background

When [glob] finds zero matching files, it raises an error.

% glob noSuchFile
no files matched glob pattern "noSuchFile"

This is unfortunate because when using [glob], finding zero matches is no more an indication of error than finding one or finding 42. Using [catch] to deal with this misfeature was an annoying burden, and in the days before [try] and a strong deployment of --errorcode values, it was burdensome to distinguish the caught circumstance of zero matches from true error conditions like a file system failure, or a syntax error in argument substitution.

The -nocomplain option was added to [glob] long ago. It was in place at least by Tcl 8.0. When present, this option disables the treatment of any empty result as an error.

% glob -nocomplain noSuchFile
%

With this option, the [glob] command could be used more effectively and robustly.

In hindsight, [glob -nocomplain] is the better primitive, and should have been the original behavior of the command. For a new major release, [glob] can become what it should have been in the first place.

Specification

Revise [glob] so that it does not raise an error when no matches are found.

Keep accepting -nocomplain as an option, but it has no effect.

Compatibility

The only compatibility issue is with any programmer who wants [glob] to raise an error when no matches are found. It is believed this will be a very uncommon desire.

Such a programmer can create a proc to post-process an empty list returned by [glob] into an error. Tcl namespaces then allow the programmer to favor his proc over the built-in command, or even to replace the built-in with it when circumstances make that sensible.

Reference Implementation

This change has long been implemented in the novem branch, and should not be difficult to extract and apply.

Copyright