Index: openacs-4/packages/acs-tcl/tcl/utilities-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-tcl/tcl/utilities-procs.tcl,v
diff -u -r1.189.2.171 -r1.189.2.172
--- openacs-4/packages/acs-tcl/tcl/utilities-procs.tcl	28 Nov 2023 15:55:08 -0000	1.189.2.171
+++ openacs-4/packages/acs-tcl/tcl/utilities-procs.tcl	26 Feb 2024 11:09:06 -0000	1.189.2.172
@@ -3239,7 +3239,7 @@
     set sv 1
 
     try {
-        exec -ignorestderr diff -f $old_f $new_f
+        exec -ignorestderr [util::which diff] -f $old_f $new_f
     } on error {output} {
     } on ok {output} {
     }
@@ -3445,37 +3445,53 @@
 
     @author Gustaf Neumann
 } {
-    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 $::env(PATH) :]
-            set exts       [list ""]
-        }
+    set key ::acs::which($prog)
+
+    if {[info exists $key]} {
+        return [set $key]
     }
-    foreach dir $searchdirs {
-        set fullname [ad_file join $dir $prog]
-        foreach ext $exts {
-            if {[ad_file executable $fullname$ext]} {
-                return $fullname$ext
+    if {$prog ne ""} {
+        
+        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 ""]
+            }
+        }       
+        set names [lmap ext $exts {set _ $prog$ext}]
+        if {[ad_file pathtype $prog] ne "relative"} {
+            set fullNames $names
+        } else {
+            set fullNames {}
+            foreach dir $searchdirs {
+                foreach name $names {
+                    lappend fullNames [ad_file join $dir $name]
+                }
+            }
         }
+        foreach fullName $fullNames {
+            if {[ad_file executable $fullName]} {
+                return [set $key $fullName]
+            }
+        }
     }
     return ""
 }
Index: openacs-4/packages/acs-tcl/tcl/test/acs-tcl-test-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-tcl/tcl/test/acs-tcl-test-procs.tcl,v
diff -u -r1.71.2.59 -r1.71.2.60
--- openacs-4/packages/acs-tcl/tcl/test/acs-tcl-test-procs.tcl	23 Feb 2024 13:14:08 -0000	1.71.2.59
+++ openacs-4/packages/acs-tcl/tcl/test/acs-tcl-test-procs.tcl	26 Feb 2024 11:09:06 -0000	1.71.2.60
@@ -1549,40 +1549,100 @@
 # This test could be used to make sure binaries in use in the code are
 # actually available to the system.
 #
-# aa_register_case -cats {
-#     smoke production_safe
-# } -procs {
-#     util::which
-#     apm_tar_cmd
-#     apm_gzip_cmd
-#     db_get_pgbin
-#     db_name
-# } acs_tcl_exec_dependencies {
-#     Test external command dependencies for this package.
-# } {
-#     set commands [list \
-#                       [::util::which [apm_tar_cmd]] \
-#                       [::util::which [apm_gzip_cmd]] \
-#                       [parameter::get -parameter "HtmlDocBin" -default "/usr/bin/htmldoc"] \
-#                       [::util::which pdfinfo] \
-#                       [::util::which diff] \
-#                       [::util::which dot] \
-#                       [::util::which gzip] \
-#                       [::util::which curl] \
-#                      ]
 
-#     if {[db_name] eq "PostgreSQL"} {
-#         #
-#         # On a Posgtgres-enabled installation, we also want psql.
-#         #
-#         lappend commands [file join [db_get_pgbin] psql]
-#     }
+ad_proc -private _acs_tcl__acs_tcl_external_dependencies_helper {} {
+} {
+    lappend required \
+        [apm_gzip_cmd] \
+        [apm_tar_cmd] \
+        [image::identify_binary] \
+        [image::convert_binary] \
+        convert \
+        curl \
+        egrep \
+        file \
+        gzip \
+        gzip \
+        identify \
+        tar 
+        
+    lappend optional \
+        [parameter::get -parameter "HtmlDocBin" -default "htmldoc"] \
+        aspell \
+        clamdscan \
+        date \
+        diff \
+        dot \
+        find \
+        hostname \
+        ispell \
+        openssl \
+        pdfinfo \
+        qrencode \
+        tail \
+        tesseract \
+        tidy \
+        uptime \
+        wget \
+        xargs \
+        zdump 
+    
+    if {[db_name] eq "PostgreSQL"} {
+        #
+        # On a Posgtgres-enabled installation, we also want psql.
+        #
+        lappend required [file join [db_get_pgbin] psql]
+    }
+    return [list required $required optional $optional]
+}
 
-#     foreach cmd $commands {
-#         aa_true "'$cmd' is executable" [file executable $cmd]
-#     }
-# }
+aa_register_case -cats {
+    smoke production_safe
+} -procs {
+    util::which
+    apm_tar_cmd
+    apm_gzip_cmd
+    db_get_pgbin
+    db_name
+    image::identify_binary
+    image::convert_binary
+} acs_tcl_exec_required_dependencies {
+    Test availability of required external commands.
+} {
+    set d [_acs_tcl__acs_tcl_external_dependencies_helper]
 
+    foreach cmd [dict get $d required] {
+        set fullCmd [::util::which $cmd]
+        aa_true "'$cmd' exists" {$fullCmd ne ""}
+        if {$fullCmd ne ""} {
+            aa_true "'$cmd' is executable" [file executable $fullCmd]
+        }
+    }
+}
+
+aa_register_case -cats {
+    smoke production_safe
+} -error_level warning -procs {
+    util::which
+    apm_tar_cmd
+    apm_gzip_cmd
+    db_get_pgbin
+    db_name
+    image::identify_binary
+    image::convert_binary
+} acs_tcl_exec_optional_dependencies {
+    Test availability of optional external commands.
+} {
+    set d [_acs_tcl__acs_tcl_external_dependencies_helper]
+
+    foreach cmd [dict get $d optional] {
+        set fullCmd [::util::which $cmd]
+        aa_true "'$cmd' exists" {$fullCmd ne ""}
+        if {$fullCmd ne ""} {
+            aa_true "'$cmd' is executable" [file executable $fullCmd]
+        }
+    }
+}
 # Local variables:
 #    mode: tcl
 #    tcl-indent-level: 4