Add OpenExternal, a function for opening files in the OS

doc/ref/streams.xml

@@ -298,6 +298,19 @@ separation character (usually a comma).
 <#Include Label="PrintCSV">
 
 </Section>
+
+<!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->
+<Section Label="Opening files in the Operating System">
+<Heading>Opening files in the Operating System</Heading>
+
+In some situations it can be desirable to open a file outside of &GAP;,
+for example HTML files, PDFs, or pictures.
+
+<#Include Label="OpenExternal">
+
+</Section>
+
+
 </Chapter>
 
 <!-- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -->

lib/streams.gd

@@ -1232,3 +1232,21 @@ DeclareGlobalFunction( "UnInstallCharReadHookFunc" );
 ##  <#/GAPDoc>
 ##
 DeclareGlobalFunction( "InputFromUser" );
+
+#############################################################################
+##
+#F  OpenExternal( <filename> )
+##
+##  <#GAPDoc Label="OpenExternal">
+##  <ManSection>
+##  <Func Name="OpenExternal" Arg='filename'/>
+##
+##  <Description>
+##  Open the file <A>filename</A> using the standard application for this file
+##  provided by the operating system. This can be used to open files like HTML and PDF
+##  files in the GUI.
+##  </Description>
+##  </ManSection>
+##  <#/GAPDoc>
+##
+DeclareGlobalFunction( "OpenExternal" );

lib/streams.gi

@@ -1388,6 +1388,22 @@ InstallGlobalFunction( InputFromUser,
   end );
 
 
+#############################################################################
+##
+#M  OpenExternal(filename)  . . . . . . . . . . . . open file in external GUI
+##
+InstallGlobalFunction( OpenExternal, function(filename)
+    if ARCH_IS_MAC_OS_X() then
+      Exec(Concatenation("open \"",filename,"\""));
+    elif ARCH_IS_WINDOWS() then
+      Exec(Concatenation("cmd /c start \"",filename,"\""));
+    elif ARCH_IS_WSL() then
+      Exec(Concatenation("explorer.exe \"$(wslpath -a -w \"",filename, "\")\""));
+    else
+      Exec(Concatenation("xdg-open \"",filename,"\""));
+    fi;
+end );
+
 
 #############################################################################
 ##