Tcl 8.3 introduces some new options to ''glob'' which generally make scripts more robust and cross-platform.  For example, they help to avoid incorrect usage like:

 glob $dir/*
 glob [file join $dir *]

which both fail if ''$dir'' contains glob sensitive characters.  The new syntax would be:

 glob -dir $dir *

which besides fixing the above problem has the added benefit of working on MacOS, since '/' is not assumed to be the directory separator.

If you want to write code using the new glob flags/options, such as ''glob -dir $dir -type d *'', obviously your new code will no longer work with older versions of Tcl (e.g. 8.0-8.2).  If you would like a compatibility layer which can be loaded into Tcl 8.0-8.2 (probably even older versions of Tcl too), overriding the old glob to emulate the new one in Tcl 8.3, here it is:

    if {[info tclversion] < 8.3} {
	;proc getOpts {{take_value ""} {set "set"}} {
	    upvar args a
	    upvar opts o
	    while {[string match \-* [set arg [lindex $a 0]]]} {
		set a [lreplace $a 0 0]
		if {$arg == "--"} {
		    return
		} else {
		    if {[set idx [lsearch -regexp $take_value \
		      "^-?[string range $arg 1 end]( .*)?$"]] == -1} {
			set o($arg) 1
		    } else {
			if {[llength [set the_arg \
			  [lindex $take_value $idx]]] == 1} {
			    $set o($arg) [lindex $a 0]
			    set a [lreplace $a 0 0]
			} else {
			    set numargs [expr {[lindex $the_arg 1] -1}]
			    $set o($arg) [lrange $a 0 $numargs]
			    set a [lreplace $a 0 $numargs]
			}
		    }
		}
	    }
	}
	rename glob __glob
	;proc glob {args} {
	    getOpts {-t -types -type -dir -path}
	    # place platform specific file separator in variable 'separator's
	    regexp {Z(.)Z} [file join Z Z] "" separator
	    if {[info exists opts(-join)]} {
		unset opts(-join)
		set args [list [eval file join $args]]
	    }
	    set add ""
	    foreach t {type types} {
		if {[info exists opts(-$t)]} {
		    eval lappend opts(-t) $opts(-$t)
		    unset opts(-$t)
		}
	    }
	    if {[info exists opts(-t)]} {
		if {[set item [lsearch -exact $opts(-t) "d"]] != -1} {
		    set opts(-t) [lreplace $opts(-t) $item $item]
		    set add $separator
		    set isdir 1
		}
	    }
	    if {[set nocomplain [info exists opts(-nocomplain)]]} {
		unset opts(-nocomplain)
	    }
	    if {[info exists opts(-path)]} {
		if {[info exists opts(-dir)]} {
		    if {$nocomplain} {
			return ""
		    } else {
			error "Can't use option '-dir' with '-path'"
		    }
		}
		regsub -all {[][*?\{\}\\]} $opts(-path) {\\&} prefix
		unset opts(-path)
	    } elseif {[info exists opts(-dir)]} {
		regsub -all {[][*?\{\}\\]} $opts(-dir) {\\&} prefix
		append prefix ${separator}
		unset opts(-dir)
	    } else {
		set prefix ""
	    }
	    set res {}
	    foreach arg $args {
		eval lappend res [__glob -nocomplain -- \
		  "${prefix}${arg}${add}"]
	    }
	    if {[info exists opts(-t)]} {
		# we ignore arguments to -t which haven't yet been handled,
		# since they are assumed to be platform specific
		unset opts(-t)
	    }
	    if {[set llen [llength [array names opts]]]} {
		set ok "-nocomplain, -join, -dir <dir>,\
		  -path <path>, -types <list of types>"
		if {$llen > 1} {
		    error "bad switches \"[array names opts]\":\
		      must be $ok or --"
		} else {
		    error "bad switch \"[array names opts]\":\
		      must be $ok or --"
		}
	    } elseif {[llength $res]} {
		if {[info exists isdir]} {
		    foreach r $res {
			lappend newres [string trimright $r $separator]
		    }
		    return $newres
		} else {
		    return $res
		}
	    } elseif {$nocomplain} {
		return ""
	    } else {
		switch -- [llength $args] {
		    0 {
			error "wrong # args: should be \"glob ?switches?\
			  name ?name ...?\""
		    }
		    1 {
			error "no files matched glob pattern \"$args\""
		    }
		    default {
			error "no files matched glob patterns \"$args\""
		    }
		}
	    }
	}
    }
--

I'm confused.  Can you show some old code that breaks?

By the way, I assume you meant to say "if you want your OLD glob code to work ..."

Vince: hopefully the clarification above solves your confusion.  The Tcl 8.3 changes to glob are 100% ''backwards'' compatible.  The goal of this page is to provide ''forwards'' compatibility for people who write 'modern' code but still want those stuck at Tcl 8.0-8.2 to be able to use it.  It handles most common uses of Tcl 8.3's glob.

''This approach deserves its own page IMO: [Forward compatibility] --jcw''