On Thu, 19 Dec 2013 12:27:09 -0600, Rick T wrote: > The following three lines are from a program that works fine for me. > > # Choose template file > use constant TMPL_FILE => > "/big/dom/xoldserver/www/templates/open_courses3.html"; my $tmpl = new > HTML::Template( filename => TMPL_FILE ); > > I wanted to make the program more portable, which means changing the > name of the server. My idea was to put the following > > my $server = “newserver” > > at the beginning of the code, then have the later lines of code use this > string. That way I’d only have to change the one line when moving to > another server. What I tried first was > > use constant TMPL_FILE => "/big/dom/x” . $server . > “/www/templates/open_courses3.html"; > > This gave me a syntax error, as did several variants I tried. I looked > up “use constant” in Learning Perl but found the discussion over my head > (I’m a beginner!), so I was hoping someone could explain a correct way > to write this code if there is one. > > > Likewise, I’d like some HTML code I use to be more portable. There, the > line that refers to a server is in a form action > > <form action="http://www.oldserver.com/cgi-bin/student_login3.cgi"; > method="post" name="FormName"> > > Again I’d like to declare the server at the top of the code. I realize > this is not strictly speaking a Perl question, but maybe there is a Perl > solution?! >
You haven't posted enough code to replicate the symptoms, but I'm guessing it boils down to: use strict; use warnings; my $server = "newserver"; use constant TMPL_FILE => "/big/dom/x" . $server . "/www/templates/open_courses3.html"; print TMPL_FILE, "\n"; Which results in: % perl foo.pl Use of uninitialized value $server in concatenation (.) or string at foo.pl line 5. /big/dom/x/www/templates/open_courses3.html A little bit of knowledge about how Perl parses and compiles code helps here. use statements are run at compile time, not execution time. The my $server = "newserver"; line is run at execution time, after the use statement is run. Therefore, $server isn't defined when the use statement attempts to create a string with it. The easiest way to fix this is to create a new constant and use that: use constant SERVER => "newserver"; use constant TMPL_FILE => "/big/dom/x" . SERVER . "/www/templates/open_courses3.html"; That gives the expected result: % perl foo.pl /big/dom/xnewserver/www/templates/open_courses3.html Diab -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
