perlfaq8 - System Interaction ($Revision: 1.26 $, $Date: 1998/08/05 12:20:28 $)
This section of the Perl FAQ covers questions involving operating system interaction. This involves interprocess communication (IPC), control over the user-interface (keyboard, screen and pointing devices), and most anything else not related to data manipulation.
Read the FAQs and documentation specific to the port of perl to your operating system (eg, the perlvms manpage, the perlplan9 manpage, ...). These should contain more detailed information on the vagaries of your perl.
The $^O variable ($OSNAME if you use English) contains the operating system that your perl binary was built for.
Because that's what it does: it replaces your currently running program with a different one. If you want to keep going (as is probably the case if you're asking this question) use
system() instead.
How you access/control keyboards, screens, and pointing devices (``mice'') is system-dependent. Try the following modules:
Term::Cap Standard perl distribution
Term::ReadKey CPAN
Term::ReadLine::Gnu CPAN
Term::ReadLine::Perl CPAN
Term::Screen CPAN
Term::Cap Standard perl distribution
Curses CPAN
Term::ANSIColor CPAN
Tk CPAN
Some of these specific cases are shown below.
In general, you don't, because you don't know whether the recipient has a color-aware display device. If you know that they have an ANSI terminal that understands color, you can use the Term::ANSIColor module from CPAN:
use Term::ANSIColor;
print color("red"), "Stop!\n", color("reset");
print color("green"), "Go!\n", color("reset");
Or like this:
use Term::ANSIColor qw(:constants);
print RED, "Stop!\n", RESET;
print GREEN, "Go!\n", RESET;
Controlling input buffering is a remarkably system-dependent matter. If most systems, you can just use the stty command as shown in getc, but as you see, that's already getting you into portability snags.
open(TTY, "+</dev/tty") or die "no tty: $!";
system "stty cbreak </dev/tty >/dev/tty 2>&1";
$key = getc(TTY); # perhaps this works
# OR ELSE
sysread(TTY, $key, 1); # probably this does
system "stty -cbreak </dev/tty >/dev/tty 2>&1";
The Term::ReadKey module from CPAN offers an easy-to-use interface that should be more efficient than shelling out to stty for each key. It even includes limited support for Windows.
use Term::ReadKey;
ReadMode('cbreak');
$key = ReadKey(0);
ReadMode('normal');
However, that requires that you have a working C compiler and can use it to build and install a CPAN module. Here's a solution using the standard POSIX module, which is already on your systems (assuming your system supports POSIX).
use HotKey;
$key = readkey();
And here's the HotKey module, which hides the somewhat mystifying calls to manipulate the POSIX termios structures.
# HotKey.pm
package HotKey;
@ISA = qw(Exporter);
@EXPORT = qw(cbreak cooked readkey);
use strict;
use POSIX qw(:termios_h);
my ($term, $oterm, $echo, $noecho, $fd_stdin);
$fd_stdin = fileno(STDIN);
$term = POSIX::Termios->new();
$term->getattr($fd_stdin);
$oterm = $term->getlflag();
$echo = ECHO | ECHOK | ICANON;
$noecho = $oterm & ~$echo;
sub cbreak {
$term->setlflag($noecho); # ok, so i don't want echo either
$term->setcc(VTIME, 1);
$term->setattr($fd_stdin, TCSANOW);
}
sub cooked {
$term->setlflag($oterm);
$term->setcc(VTIME, 0);
$term->setattr($fd_stdin, TCSANOW);
}
sub readkey {
my $key = '';
cbreak();
sysread(STDIN, $key, 1);
cooked();
return $key;
}
END { cooked() }
1;
The easiest way to do this is to read a key in nonblocking mode with the Term::ReadKey module from CPAN, passing it an argument of -1 to indicate not to block:
use Term::ReadKey;
ReadMode('cbreak');
if (defined ($char = ReadKey(-1)) ) {
# input was waiting and it was $char
} else {
# no input was waiting
}
ReadMode('normal'); # restore normal tty settings
If you only have to so infrequently, use system:
system("clear");
If you have to do this a lot, save the clear string so you can print it 100 times without calling a program 100 times:
$clear_string = `clear`;
print $clear_string;
If you're planning on doing other screen manipulations, like cursor positions, etc, you might wish to use Term::Cap module:
use Term::Cap;
$terminal = Term::Cap->Tgetent( {OSPEED => 9600} );
$clear_string = $terminal->Tputs('cl');
If you have Term::ReadKey module installed from CPAN, you can use it to fetch the width and height in characters and in pixels:
use Term::ReadKey;
($wchar, $hchar, $wpixels, $hpixels) = GetTerminalSize();
This is more portable than the raw ioctl, but not as illustrative:
require 'sys/ioctl.ph';
die "no TIOCGWINSZ " unless defined &TIOCGWINSZ;
open(TTY, "+</dev/tty") or die "No tty: $!";
unless (ioctl(TTY, &TIOCGWINSZ, $winsize='')) {
die sprintf "$0: ioctl TIOCGWINSZ (%08x: $!)\n", &TIOCGWINSZ;
}
($row, $col, $xpixel, $ypixel) = unpack('S4', $winsize);
print "(row,col) = ($row,$col)";
print " (xpixel,ypixel) = ($xpixel,$ypixel)" if $xpixel || $ypixel;
print "\n";
(This question has nothing to do with the web. See a different FAQ for that.)
There's an example of this in crypt). First, you put the terminal into ``no echo'' mode, then just read the password normally. You may do this with an old-style
ioctl() function,
POSIX terminal control (see
the POSIX manpage, and Chapter 7 of the Camel), or a call to the stty program, with varying degrees of portability.
You can also do this for most systems using the Term::ReadKey module from CPAN, which is easier to use and in theory more portable.
use Term::ReadKey;
ReadMode('noecho');
$password = ReadLine(0);
This depends on which operating system your program is running on. In the case of Unix, the serial ports will be accessible through files in /dev; on other systems, the devices names will doubtless differ. Several problem areas common to all device interaction are the following
sysopen() and
O_RDWR|O_NDELAY|O_NOCTTY from the Fcntl module (part of the standard perl distribution). See
sysopen for more on this approach.
print DEV "atv1\012"; # wrong, for some devices
print DEV "atv1\015"; # right, for some devices
Even though with normal text files, a ``\n'' will do the trick, there is still no unified scheme for terminating a line that is portable between Unix, DOS/Win, and Macintosh, except to terminate ALL line ends with ``\015\012'', and strip what you don't need from the output. This applies especially to socket I/O and autoflushing, discussed next.
print() them, you'll want to autoflush that filehandle. You can use
select() and the
$| variable to control autoflushing (see perlvar/$
and select):
$oldh = select(DEV);
$| = 1;
select($oldh);
You'll also see code that does this without a temporary variable, as in
select((select(DEV), $| = 1)[0]);
Or if you don't mind pulling in a few thousand lines of code just because you're afraid of a little $| variable:
use IO::Handle;
DEV->autoflush(1);
As mentioned in the previous item, this still doesn't work when using socket I/O between Unix and Macintosh. You'll need to hardcode your line terminators, in that case.
read() or
sysread(), you'll have to arrange for an alarm handler to provide a timeout (see
alarm). If you have a non-blocking open, you'll likely have a non-blocking read, which means you may have to use a 4-arg
select() to determine whether
I/O is ready on that device (see
select.
While trying to read from his caller-id box, the notorious Jamie Zawinski <jwz@netscape.com>, after much gnashing of teeth and fighting with sysread, sysopen, POSIX's tcgetattr business, and various other functions that go bump in the night, finally came up with this:
sub open_modem {
use IPC::Open2;
my $stty = `/bin/stty -g`;
open2( \*MODEM_IN, \*MODEM_OUT, "cu -l$modem_device -s2400 2>&1");
# starting cu hoses /dev/tty's stty settings, even when it has
# been opened on a pipe...
system("/bin/stty $stty");
$_ = <MODEM_IN>;
chop;
if ( !m/^Connected/ ) {
print STDERR "$0: cu printed `$_' instead of `Connected'\n";
}
}
You spend lots and lots of money on dedicated hardware, but this is bound to get you talked about.
Seriously, you can't if they are Unix password files - the Unix password system employs one-way encryption. It's more like hashing than encryption. The best you can check is whether something else hashes to the same string. You can't turn a hash back into the original string. Programs like Crack can forcibly (and intelligently) try to guess passwords, but don't (can't) guarantee quick success.
If you're worried about users selecting bad passwords, you should proactively check when they try to change their password (by modifying
passwd(1), for example).
You could use
system("cmd &")
or you could use fork as documented in fork, with further examples in the perlipc manpage. Some things to be aware of, if you're on a Unix-like system:
$SIG{CHLD} = sub { wait };
See Signals for other examples of code to do this. Zombies are not an issue with system("prog &").
You don't actually ``trap'' a control character. Instead, that character generates a signal which is sent to your terminal's currently foregrounded process group, which you then trap in your process. Signals are documented in Signals and chapter 6 of the Camel.
Be warned that very few
C libraries are re-entrant. Therefore, if you attempt to
print() in a handler that got invoked during another stdio operation your internal structures will likely be in an inconsistent state, and your program will dump core. You can sometimes avoid this by using
syswrite() instead of
print().
Unless you're exceedingly careful, the only safe things to do inside a signal handler are: set a variable and exit. And in the first case, you should only set a variable in such a way that
malloc() is not called (eg, by setting a variable that already has a value).
For example:
$Interrupted = 0; # to ensure it has a value
$SIG{INT} = sub {
$Interrupted++;
syswrite(STDERR, "ouch\n", 5);
}
However, because syscalls restart by default, you'll find that if you're in a ``slow'' call, such as
<FH>,
read(),
connect(), or
wait(), that the only way to terminate them is by ``longjumping'' out; that is, by raising an exception. See the time-out handler for a blocking
flock() in
Signals or chapter 6 of the Camel.
If perl was installed correctly, and your shadow library was written
properly, the getpw*() functions described in the perlfunc manpage should in theory provide (read-only) access to entries in the shadow
password file. To change the file, make a new shadow password file (the
format varies from system to system - see passwd(5) for specifics) and use
pwd_mkdb(8) to install it
(see pwd_mkdb(5) for more details).
Assuming you're running under sufficient permissions, you should be able to set the system-wide date and time by running the
date(1) program. (There is no way to set the time and date on a per-process basis.) This mechanism will work for Unix,
MS-DOS, Windows, and
NT; the
VMS equivalent is
set time.
However, if all you want to do is change your timezone, you can probably get away with setting an environment variable:
$ENV{TZ} = "MST7MDT"; # unixish
$ENV{'SYS$TIMEZONE_DIFFERENTIAL'}="-5" # vms
system "trn comp.lang.perl.misc";
If you want finer granularity than the 1 second that the
sleep() function provides, the easiest way is to use the
select() function as documented in
select. If your system has itimers and
syscall() support, you can
check out the old example in http://www.perl.com/CPAN/doc/misc/ancient/tutorial/eg/itimers.pl
.
In general, you may not be able to. The Time::HiRes module (available from CPAN) provides this functionality for some systems.
In general, you may not be able to. But if your system supports both the
syscall() function in Perl as well as a system call like
gettimeofday(2), then you may be able to do something like this:
require 'sys/syscall.ph';
$TIMEVAL_T = "LL";
$done = $start = pack($TIMEVAL_T, ());
syscall( &SYS_gettimeofday, $start, 0)) != -1
or die "gettimeofday: $!";
##########################
# DO YOUR OPERATION HERE #
##########################
syscall( &SYS_gettimeofday, $done, 0) != -1
or die "gettimeofday: $!";
@start = unpack($TIMEVAL_T, $start);
@done = unpack($TIMEVAL_T, $done);
# fix microseconds
for ($done[1], $start[1]) { $_ /= 1_000_000 }
$delta_time = sprintf "%.4f", ($done[0] + $done[1] )
-
($start[0] + $start[1] );
Release 5 of Perl added the
END block, which can be used to simulate
atexit(). Each package's
END block is called when the program or thread ends (see
the perlmod manpage manpage for more details).
For example, you can use this to make sure your filter program managed to finish its output without filling up the disk:
END {
close(STDOUT) || die "stdout close failed: $!";
}
The END block isn't called when untrapped signals kill the program, though, so if you use END blocks you should also use
use sigtrap qw(die normal-signals);
Perl's exception-handling mechanism is its
eval() operator. You can use
eval() as setjmp and
die() as longjmp. For details of this, see the section on signals, especially the time-out handler for a blocking
flock() in
Signals and chapter 6 of the Camel.
If exception handling is all you're interested in, try the exceptions.pl library (part of the standard perl distribution).
If you want the
atexit() syntax (and an
rmexit() as well), try the AtExit module available from
CPAN.
Some Sys-V based systems, notably Solaris 2.X, redefined some of the standard socket constants. Since these were constant across all architectures, they were often hardwired into perl code. The proper way to deal with this is to ``use Socket'' to get the correct values.
Note that even though SunOS and Solaris are binary compatible, these values are different. Go figure.
In most cases, you write an external module to do it - see the answer to ``Where can
I learn about linking
C with Perl? [h2xs, xsubpp]''. However, if the function is a system call, and your system supports
syscall(), you can use the syscall function (documented in
the perlfunc manpage).
Remember to check the modules that came with your distribution, and CPAN as well - someone may already have written a module to do it.
Historically, these would be generated by the h2ph tool, part of the standard perl distribution. This program converts
cpp(1) directives in
C header files to files containing subroutine definitions, like &SYS_getitimer, which you can use as arguments to your functions. It doesn't work perfectly, but it usually gets most of the job done. Simple files like
errno.h, syscall.h, and socket.h were fine, but the hard ones like ioctl.h nearly always need to hand-edited. Here's how to install the *.ph files:
1. become super-user
2. cd /usr/include
3. h2ph *.h */*.h
If your system supports dynamic loading, for reasons of portability and sanity you probably ought to use h2xs (also part of the standard perl distribution). This tool converts C header files to Perl extensions. See the perlxstut manpage for how to get started with h2xs.
If your system doesn't support dynamic loading, you still probably ought to use h2xs. See the perlxstut manpage and MakeMaker for more information (in brief, just use make perl instead of a plain make to rebuild perl with a new static extension).
Some operating systems have bugs in the kernel that make setuid scripts inherently insecure. Perl gives you a number of options (described in the perlsec manpage) to work around such systems.
The IPC::Open2 module (part of the standard perl distribution) is an easy-to-use approach that internally uses
pipe(),
fork(), and
exec() to do the job. Make sure you read the deadlock warnings in its documentation, though (see
Open2). See Bidirectional Communication with Another Process and Bidirectional Communication with Yourself
You may also use the IPC::Open3 module (part of the standard perl distribution), but be warned that it has a different order of arguments from IPC::Open2 (see Open3).
You're confusing the purpose of
system() and backticks (``).
system() runs a command and returns exit status information (as a 16 bit value: the low 7 bits are the signal the process died from, if any, and the high 8 bits are the actual exit value). Backticks (``) run a command and return what it sent to
STDOUT.
$exit_status = system("mail-users");
$output_string = `ls`;
There are three basic ways of running external commands:
system $cmd; # using system()
$output = `$cmd`; # using backticks (``)
open (PIPE, "cmd |"); # using open()
With
system(), both
STDOUT and
STDERR will go the same place as the script's versions of these, unless the command redirects them. Backticks and
open() read
only the
STDOUT of your command.
With any of these, you can change file descriptors before the call:
open(STDOUT, ">logfile");
system("ls");
or you can use Bourne shell file-descriptor redirection:
$output = `$cmd 2>some_file`;
open (PIPE, "cmd 2>some_file |");
You can also use file-descriptor redirection to make STDERR a duplicate of STDOUT:
$output = `$cmd 2>&1`;
open (PIPE, "cmd 2>&1 |");
Note that you cannot simply open STDERR to be a dup of STDOUT in your Perl program and avoid calling the shell to do the redirection. This doesn't work:
open(STDERR, ">&STDOUT");
$alloutput = `cmd args`; # stderr still escapes
This fails because the
open() makes
STDERR go to where
STDOUT was going at the time of the
open(). The backticks then make
STDOUT go to a string, but don't change
STDERR (which still goes to the old
STDOUT).
Note that you must use Bourne shell (sh(1)) redirection syntax in backticks, not
csh(1)! Details on why Perl's
system() and backtick and pipe opens all use the Bourne shell are in http://www.perl.com/CPAN/doc/FMTEYEWTK/versus/csh.whynot . To capture a command's
STDERR and
STDOUT together:
$output = `cmd 2>&1`; # either with backticks
$pid = open(PH, "cmd 2>&1 |"); # or with an open pipe
while (<PH>) { } # plus a read
To capture a command's STDOUT but discard its STDERR:
$output = `cmd 2>/dev/null`; # either with backticks
$pid = open(PH, "cmd 2>/dev/null |"); # or with an open pipe
while (<PH>) { } # plus a read
To capture a command's STDERR but discard its STDOUT:
$output = `cmd 2>&1 1>/dev/null`; # either with backticks
$pid = open(PH, "cmd 2>&1 1>/dev/null |"); # or with an open pipe
while (<PH>) { } # plus a read
To exchange a command's STDOUT and STDERR in order to capture the STDERR but leave its STDOUT to come out our old STDERR:
$output = `cmd 3>&1 1>&2 2>&3 3>&-`; # either with backticks
$pid = open(PH, "cmd 3>&1 1>&2 2>&3 3>&-|");# or with an open pipe
while (<PH>) { } # plus a read
To read both a command's STDOUT and its STDERR separately, it's easiest and safest to redirect them separately to files, and then read from those files when the program is done:
system("program args 1>/tmp/program.stdout 2>/tmp/program.stderr");
Ordering is important in all these examples. That's because the shell processes file descriptor redirections in strictly left to right order.
system("prog args 1>tmpfile 2>&1");
system("prog args 2>&1 1>tmpfile");
The first command sends both standard out and standard error to the temporary file. The second command sends only the old standard output there, and the old standard error shows up on the old standard out.
It does, but probably not how you expect it to. On systems that follow the standard
fork()/exec() paradigm (such as Unix), it works like this:
open() causes a
fork(). In the parent,
open() returns with the process
ID of the child. The child
exec()s the command to be piped to/from. The parent can't know whether the
exec() was successful or not - all it can return is whether the
fork() succeeded or not. To find out if the command succeeded, you have to catch
SIGCHLD and
wait() to get the exit status. You should also catch
SIGPIPE if you're writing to the child -- you may not have found out the
exec() failed by the time you write. This is documented in
the perlipc manpage.
On systems that follow the
spawn() paradigm,
open()
might do what you expect - unless perl uses a shell to start your command. In this case the
fork()/exec() description still applies.
Strictly speaking, nothing. Stylistically speaking, it's not a good way to write maintainable code because backticks have a (potentially humungous) return value, and you're ignoring it. It's may also not be very efficient, because you have to read in all the lines of output, allocate memory for them, and then throw it away. Too often people are lulled to writing:
`cp file file.bak`;
And now they think ``Hey, I'll just always use backticks to run programs.'' Bad idea: backticks are for capturing a program's output; the
system() function is for running programs.
Consider this line:
`cat /etc/termcap`;
You haven't assigned the output anywhere, so it just wastes memory (for a
little while). Plus you forgot to check $? to see whether the program even ran correctly. Even if you wrote
print `cat /etc/termcap`;
In most cases, this could and probably should be written as
system("cat /etc/termcap") == 0
or die "cat program failed!";
Which will get the output quickly (as its generated, instead of only at the end) and also check the return value.
system() also provides direct
control over whether shell wildcard processing may take place, whereas
backticks do not.
This is a bit tricky. Instead of writing
@ok = `grep @opts '$search_string' @filenames`;
You have to do this:
my @ok = ();
if (open(GREP, "-|")) {
while (<GREP>) {
chomp;
push(@ok, $_);
}
close GREP;
} else {
exec 'grep', @opts, $search_string, @filenames;
}
Just as with
system(), no shell escapes happen when you
exec() a list.
There are more examples of this Safe Pipe Opens.
Because some stdio's set error and eof flags that need clearing. The
POSIX module defines
clearerr() that you can use. That is the technically correct way to do it. Here are some less reliable workarounds:
Try keeping around the seekpointer and go there, like this:
$where = tell(LOG);
seek(LOG, $where, 0);
If that doesn't work, try seeking to a different part of the file and then back.
Learn Perl and rewrite it. Seriously, there's no simple converter. Things that are awkward to do in the shell are easy to do in Perl, and this very awkwardness is what would make a shell->perl converter nigh-on impossible to write. By rewriting it, you'll think about what you're really trying to do, and hopefully will escape the shell's pipeline datastream paradigm, which while convenient for some matters, causes many inefficiencies.
Try the Net::FTP, TCP::Client, and Net::Telnet modules (available from CPAN). http://www.perl.com/CPAN/scripts/netstuff/telnet.emul.shar will also help for emulating the telnet protocol, but Net::Telnet is quite probably easier to use..
If all you want to do is pretend to be telnet but don't need the initial telnet handshaking, then the standard dual-process approach will suffice:
use IO::Socket; # new in 5.004
$handle = IO::Socket::INET->new('www.perl.com:80')
|| die "can't connect to port 80 on www.perl.com: $!";
$handle->autoflush(1);
if (fork()) { # XXX: undef means failure
select($handle);
print while <STDIN>; # everything from stdin to socket
} else {
print while <$handle>; # everything from socket to stdout
}
close $handle;
exit;
Once upon a time, there was a library called chat2.pl (part of the standard perl distribution), which never really got finished. If you find it somewhere, don't use it. These days, your best bet is to look at the Expect module available from CPAN, which also requires two other modules from CPAN, IO::Pty and IO::Stty.
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 the perlvar manpage. This won't work on all operating systems, though. Daemon programs like
sendmail place their state there, as in:
$0 = "orcus [accepting connections]";
eval()ing the script's output in your shell; check out the comp.unix.questions
FAQ for details.
Assuming your system supports such things, just send an appropriate signal to the process (see kill. It's common to first send a TERM signal, wait a little bit, and then send a KILL signal to finish it off.
If by daemon process you mean one that's detached (disassociated from its tty), then the following process is reported to work on most Unixish systems. Non-Unix users should check their Your_OS::Process module for other solutions.
Open /dev/tty and use the the TIOCNOTTY ioctl on it. See tty(4) for details. Or better yet, you can just use the POSIX::setsid() function, so you don't have to worry about process groups.
fork && exit;
See the eg/nih script (part of the perl source distribution).
Good question. Sometimes -t STDIN and -t STDOUT can give clues, sometimes not.
if (-t STDIN && -t STDOUT) {
print "Now what? ";
}
On POSIX systems, you can test whether your own process group matches the current process group of your controlling terminal as follows:
use POSIX qw/getpgrp tcgetpgrp/;
open(TTY, "/dev/tty") or die $!;
$tpgrp = tcgetpgrp(TTY);
$pgrp = getpgrp();
if ($tpgrp == $pgrp) {
print "foreground\n";
} else {
print "background\n";
}
Use the
alarm() function, probably in
conjunction with a signal handler, as documented Signals and chapter 6 of the Camel. You may instead use the more flexible Sys::AlarmCall module available from
CPAN.
Use the BSD::Resource module from CPAN.
Use the reaper code from Signals to call
wait() when a
SIGCHLD is received, or else use the double-fork technique described in
fork.
There are a number of excellent interfaces to SQL databases. See the DBD::* modules available from http://www.perl.com/CPAN/modules/dbperl/DBD . A lot of information on this can be found at http://www.hermetica.com/technologia/perl/DBI/index.html .
You can't. You need to imitate the
system() call (see the perlipc manpage for sample code) and then have a signal handler for the
INT signal that passes the signal on to the
subprocess. Or you can check for it:
$rc = system($cmd);
if ($rc & 127) { die "signal death" }
If you're lucky enough to be using a system that supports non-blocking reads (most Unixish systems do), you need only to use the
O_NDELAY or
O_NONBLOCK flag from the Fcntl module in conjunction with
sysopen():
use Fcntl;
sysopen(FH, "/tmp/somefile", O_WRONLY|O_NDELAY|O_CREAT, 0644)
or die "can't open /tmp/somefile: $!":
The easiest way is to have the CPAN module do it for you. This module comes with perl version 5.004 and later. To manually install the CPAN module, or any well-behaved CPAN module for that matter, follow these steps:
Unpack the source into a temporary area.
perl Makefile.PL
make
make test
make install
If your version of perl is compiled without dynamic loading, then you just need to replace step 3 (make) with make perl and you will get a new perl binary with your extension linked in.
See MakeMaker for more details on building extensions. See also the next question.
Perl offers several different ways to include code from one file into another. Here are the deltas between the various inclusion constructs:
1) do $file is like eval `cat $file`, except the former:
1.1: searches @INC and updates %INC.
1.2: bequeaths an *unrelated* lexical scope on the eval'ed code.
2) require $file is like do $file, except the former:
2.1: checks for redundant loading, skipping already loaded files.
2.2: raises an exception on failure to find, compile, or execute $file.
3) require Module is like require "Module.pm", except the former:
3.1: translates each "::" into your system's directory separator.
3.2: primes the parser to disambiguate class Module as an indirect object.
4) use Module is like require Module, except the former:
4.1: loads the module at compile time, not run-time.
4.2: imports symbols and semantics from that package to the current one.
In general, you usually want use and a proper Perl module.
When you build modules, use the PREFIX option when generating Makefiles:
perl Makefile.PL PREFIX=/u/mydir/perl
then either set the PERL5LIB environment variable before you run scripts that use the modules/libraries (see the perlrun manpage) or say
use lib '/u/mydir/perl';
See Perl's the lib manpage for more information.
use FindBin;
use lib "$FindBin::Bin";
use your_own_modules;
Here are the suggested ways of modifying your include path:
the PERLLIB environment variable
the PERL5LIB environment variable
the perl -Idir commpand line flag
the use lib pragma, as in
use lib "$ENV{HOME}/myown_perllib";
The latter is particularly useful because it knows about machine dependent architectures. The lib.pm pragmatic module was first included with the 5.002 release of Perl.
Copyright (c) 1997, 1998 Tom Christiansen and Nathan Torkington. All rights reserved.
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