util::which (public)

 util::which prog

Defined in packages/acs-tcl/tcl/utilities-procs.tcl

Use environment variable PATH to search for the specified executable program. Replacement for UNIX command "which", avoiding exec. exec which: 3368.445 microseconds per iteration ::util::which: 282.372 microseconds per iteration In addition of being more than 10 time faster than the version via exec, this version is less platform dependent.

prog - name of the program to be located on the search path
fully qualified name including path, when specified program is found, or otherwise empty string
Gustaf Neumann
Source code:
    switch $::tcl_platform(platform) {
        windows {
            # Notice: Windows has an alternative search environment 
            #         via registry. Maybe it is necessary in the future
            #         to locate the program via registry (sketch below)
            # package require registry
            # set key {HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths}
            # set entries [registry keys $key $prog.*]
            # if {[llength $entries]>0} {
            #   set fullkey "$key\\[lindex $entries 0]"
            #   return [registry get $fullkey ""]
            # }
            # return ""
            set searchdirs [split $::env(PATH) \;] 
            set exts       [list .exe .dll .com .bat]
        default { 
            set searchdirs [split $::env(PATH) :] 
            set exts       [list ""]
    foreach dir $searchdirs {
        set fullname [file join $dir $prog]
        foreach ext $exts {
            if {[file executable $fullname$ext]} {
                return $fullname$ext
    return ""
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