This is an excerpt from the latest version perlfaq8.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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

8.26: Why doesn't open() return an error when a pipe open fails?

If the second argument to a piped open() contains shell metacharacters,
perl fork()s, then exec()s a shell to decode the metacharacters and
eventually run the desired program. If the program couldn't be run, it's
the shell that gets the message, not Perl. All your Perl program can
find out is whether the shell itself could be successfully started. You
can still capture the shell's STDERR and check it for error messages.
See "How can I capture STDERR from an external command?" elsewhere in
this document, or use the IPC::Open3 module.

If there are no shell metacharacters in the argument of open(), Perl
runs the command directly, without using the shell, and can correctly
report whether the command started.

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

This is an excerpt from the latest version perlfaq8.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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

8.33: Is there a way to hide perl's command line from programs such as "ps"?

First of all note that if you're doing this for security reasons (to
avoid people seeing passwords, for example) then you should rewrite your
program so that critical information is never given as an argument.
Hiding the arguments won't make your program completely secure.

To actually alter the visible command line, you can assign to the
variable $0 as documented in perlvar. This won't work on all operating
systems, though. Daemon programs like sendmail place their state there,
as in:

$0 = "orcus [accepting connections]";

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have designed and developed Graphing tools and Math/Stats online
software that is available on internet. Most of my visitor are from US
academia. The list of programs include the following

1. Graphing Rectangular 2D
2. Graphing Rectangular 3D
3. Graphing Polar
4. Graphing 2D Parametric curves
5. Graphing 3D Parametric curves
6. Graphing 3D Parametric surfaces

I'm running build 813 on 'doze XP/Home. I want my Perl script to
determine the directory from which it was run. This is equivalent to
retrieving the command line. For example, from a DOS window I type:

I want the script to be able to retrieve the string "c:\mydir".

There is a Win32 function, Find, that can look for files, but it only
searches the INC directories, so it is not reliable.

Any ideas, please.

This is an excerpt from the latest version perlfaq8.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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

8.27: What's wrong with using backticks in a void context?

Strictly speaking, nothing. Stylistically speaking, it's not a good way
to write maintainable code. Perl has several operators for running
external commands. Backticks are one; they collect the output from the
command for use in your program. The "system" function is another; it
doesn't do this.

Writing backticks in your program sends a clear message to the readers
of your code that you wanted to collect the output of the command. Why
send a clear message that isn't true?

Consider this line:

`cat /etc/termcap`;

You forgot to check $? to see whether the program even ran correctly.
Even if you wrote

This is an excerpt from the latest version perlfaq8.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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

8.39: How do I set CPU limits?

(contributed by Xho)

Use the "BSD::Resource" module from CPAN. As an example:

use BSD::Resource;
setrlimit(RLIMIT_CPU,10,20) or die $!;

This sets the soft and hard limits to 10 and 20 seconds, respectively.
After 10 seconds of time spent running on the CPU (not "wall" time), the
process will be sent a signal (XCPU on some systems) which, if not
trapped, will cause the process to terminate. If that signal is trapped,
then after 10 more seconds (20 seconds in total) the process will be
killed with a non-trappable signal.

See the "BSD::Resource" and your systems documentation for the gory
details.