Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!exodus!snave.Eng.Sun.COM!matt
From: matt@snave.Eng.Sun.COM (Matt Evans)
Newsgroups: comp.lang.perl
Subject: new user findings
Message-ID: <13850@exodus.Eng.Sun.COM>
Date: 23 May 91 00:01:41 GMT
Sender: news@exodus.Eng.Sun.COM
Reply-To: matt@snave.Eng.Sun.COM (Matt Evans)
Distribution: na
Organization: Sun Microsystems, Inc.  Mt. View, Ca.
Lines: 144



Hello Perl users;


I've just started using perl (perl 4.0 on SUNOS 4.1.1 sun4c) and I 
have some questions relating to the following problems I
seen ...


=======================
 1) caller command:
=======================


   PERL core dumps on the following 
   code:


#!/usr/local/bin/perl
#---------------------------
# start test (caller) main
#---------------------------

   $prog_dir = "./";
   $prog_name = "not_here";


   open (ERR_LOG,">./perr");

   $proc_name = join ("",$prog_dir,$prog_name);
   if (!( -e $conv_proc_name)) {
	&conv_err ("can't access the program",1);
   }

sub conv_err {

    local($err_msg,$err_code) = @_; # sub arguments


    #
    # local variable declaration
    #

    local($pack);      
    local($file);      
    local($line);      
    local($sub_name); 


    #
    # after debugging the core file, it seems perl
    # dies on the next line
    #


    ($pack,$file,$line,$sub_name) = caller (0);


    if ($err_code == $FATAL_ERR) {
       print ERR_LOG "\n\n ERROR:$pack:$sub_name:$file:$line";
       die "exit test tool";
    }
    else {
          print ERR_LOG "\n\n ERROR:$pack:$sub_name:$file:$line";
    }
   
}

================================
 2) numeric & string equalities
================================

 In reading the camel book, it seems there should be no problem
 in comparing strings and numbers, However the behavior of the 
 following perl code seems inconsistent:


#!/asdf/bin/perl

 $x = "test";
 if ($x == 0) {
    print "x is equal to 0\n";
 }
 if ($x eq "test") {
    print "x is equal to the str \"test\"\n";
 }

 ------------------------------------------

 output:

 x is equal to 0
 x is equal to the str "test"


 Question: Why does $x compare equally to numeric 0? Is this
	   correct behavior?
 

================================
 3) tom christiansen's open2.pl
================================

 This is more of a question and a FYI. I was using the open2.pl
 routine to fire off a process from perl. The routine works
 like a champ, but it has an interesting side effect. This side
 effect actually occurs in the spawned process. The spawned
 process I was running does an fstat on STDIN to tell if it
 has been started interactively from a terminal  or if it
 has been spawned using pipes. (this C program does many things
 differently based on whether it is started from pipes or
 a character device).

   C code snipit:

     if ((sbuf.st_mode & S_IFMT) == S_IFCHR) {
        input_term = TRUE;
     }
     else {
           input_term = FALSE;
     }

 well, if the process is started from perl using open2.pl the
 process thinks it was started from a terminal i.e from above
 the var input_term is assigned to TRUE.

 I wrote  C program to emulate open2.pl with the sequence
 of using pipe,fork then exec. The above process did in fact
 register that it is NOT started from a terminal and the C statement
 (sbuf.st_mode & S_IFMT) is actually equal to S_IFIFO. This is
 also true if a process is started from the sh pipe ('|') .

 So the question goes to all the perl internals wizards:

 Is there any hidden things happening with PERL's pipe, fork 
 and exec commands that would explain the results I'm getting from
 that fstat routine on the spawned program? 
 

thanks in advance for helpin' a perl neophyte!

 
Matt Evans