if {([package vcompare [package provide Tcl] 7.6] < 0)
          && [string match unix $tcl_platform(platform)]} {

    # The subcommands copy, delete, rename, and mkdir were added to
    # the Tcl command 'file' in Tcl version 7.6.  The following command
    # approximates them on Unix platforms.  It may not agree with
    # the Tcl 7.6+ command 'file' in all of its functionality (notably
    # the way it reports errors).  Further refinements should be made as
    # needed.
    rename file Tcl7.5_file
    proc file {option args} {
        switch -glob -- $option {
            c* {
                if {[string first $option copy] != 0} {
                    return [uplevel [list Tcl7.5_file $option] $args]
                }
                # Translate -force into -f
                if {[string match -force [lindex $args 0]]} {
                    set args [lreplace $args 0 0 -f]
                }
                uplevel exec cp $args
            }
            de* {
                if {[string first $option delete] != 0} {
                    return [uplevel [list Tcl7.5_file $option] $args]
                }
                if {[string match -force [lindex $args 0]]} {
                    set args [lreplace $args 0 0 -f]
                }
                catch {uplevel exec rm $args}
            }
            mk* {
                if {[string first $option mkdir] != 0} {
                    return [uplevel [list Tcl7.5_file $option] $args]
                }
                uplevel exec mkdir $args
            }
            ren* {
                if {[string first $option rename] != 0} {
                    return [uplevel [list Tcl7.5_file $option] $args]
                }
                if {[string match -force [lindex $args 0]]} {
                    set args [lreplace $args 0 0 -f]
                }
                uplevel exec mv $args
            }
            default {
                uplevel [list Tcl7.5_file $option] $args
            }
        }
    }
  }

  if {[package vcompare [package provide Tcl] 8] < 0} {

    # The subcommands nativename and attributes were added to
    # the Tcl command 'file' in Tcl version 8.0.  Here is an approximation
    # for earlier Tcl versions:
    rename file Tcl7.6_file
    ;proc file {option args} {
        switch -glob -- $option {
            att* {
                if {[string first $option attributes] != 0} {
                    uplevel [list Tcl7.6_file $option] $args
                }
                return -code error "Tcl [package provide Tcl] does not support\
			\[file attributes\].\n\tUpgrade to Tcl 8.0 to use it."
            }
            n* {
                if {[string first $option nativename] != 0} {
                    uplevel [list Tcl7.6_file $option] $args
                }
                if {![llength $args]} {
                    return -code error "wrong # args: should be\
                	    \"file nativename name ?arg ...?\""
                }
                set fcomps [file split [lindex $args 0]]
                # Take care of tilde substitution
                set first [lindex $fcomps 0]
                if {[string match ~* $first]} {
                    set first [file join [file dirname $first] [file tail $first]]
                }
                set result [eval file join [list $first] [lrange $fcomps 1 end]]
                global tcl_platform
                if {[string match windows $tcl_platform(platform)]} {
                    regsub -all -- / $result \\ result
                }
                return $result
            }
            default {
                uplevel [list Tcl7.6_file $option] $args
            }
        }
    }
  }

----
[Category Porting]