[6804] in Perl-Users-Digest
Perl-Users Digest, Issue: 429 Volume: 8
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Mon May 5 02:17:25 1997
Date: Sun, 4 May 97 23:04:42 -0700
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Sun, 4 May 1997 Volume: 8 Number: 429
Today's topics:
Perl FAQ part 8 of 0..9: System Interaction [Periodic P <perlfaq-suggestions@mox.perl.com>
Perl FAQ part 9 of 0..9: Networking [Periodic Posting] <perlfaq-suggestions@mox.perl.com>
Perl on Win95? <peter@webcanada.com>
Digest Administrivia (Last modified: 8 Mar 97) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: 4 May 1997 22:00:54 GMT
From: PerlFAQ <perlfaq-suggestions@mox.perl.com>
Subject: Perl FAQ part 8 of 0..9: System Interaction [Periodic Posting]
Message-Id: <5kj0um$9p5$1@csnews.cs.colorado.edu>
NAME
perlfaq8 - System Interaction
($Revision: 1.21 $, $Date: 1997/04/24 22:44:19 $)
DESCRIPTION
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.
How do I find out which operating system I'm running under?
The $^O variable ($OSTYPE if you use English) contains the operating
system that your perl binary was built for.
How come exec() doesn't return?
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 do I do fancy stuff with the keyboard/screen/mouse?
How you access/control keyboards, screens, and pointing devices
("mice") is system-dependent. Try the following modules:
Keyboard
Term::Cap Standard perl distribution
Term::ReadKey CPAN
Term::ReadLine::Gnu CPAN
Term::ReadLine::Perl CPAN
Term::Screen CPAN
Screen
Term::Cap Standard perl distribution
Curses CPAN
Term::ANSIColor CPAN
Mouse
Tk CPAN
How do I ask the user for a password?
(This question has nothing to do with the web. See a different FAQ for
that.)
There's an example of this in the "crypt" entry in the perlfunc
manpage). 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.
How do I read and write the serial port?
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
lockfiles
Your system may use lockfiles to control multiple access. Make
sure you follow the correct protocol. Unpredictable behaviour can
result from multiple processes reading from one device.
open mode
If you expect to use both read and write operations on the device,
you'll have to open it for update (see the section on "open" in
the perlfunc manpage for details). You may wish to open it without
running the risk of blocking by using sysopen() and
`O_RDWR|O_NDELAY|O_NOCTTY' from the Fcntl module (part of the
standard perl distribution). See the section on "sysopen" in the
perlfunc manpage for more on this approach.
end of line
Some devices will be expecting a "\r" at the end of each line
rather than a "\n". In some ports of perl, "\r" and "\n" are
different from their usual (Unix) ASCII values of "\012" and
"\015". You may have to give the numeric values you want directly,
using octal ("\015"), hex ("0x0D"), or as a control-character
specification ("\cM").
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.
flushing output
If you expect characters to get to your device when you print()
them, you'll want to autoflush that filehandle, as in the older
use FileHandle;
DEV->autoflush(1);
and the newer
use IO::Handle;
DEV->autoflush(1);
You can use select() and the `$|' variable to control autoflushing
(see the section on "$|" in the perlvar manpage and the "select"
entry in the perlfunc manpage):
$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]);
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.
non-blocking input
If you are doing a blocking read() or sysread(), you'll have to
arrange for an alarm handler to provide a timeout (see the "alarm"
entry in the perlfunc manpage). 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 the section on "select" in the perlfunc manpage.
How do I decode encrypted password files?
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. 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).
How do I start a process in the background?
You could use
system("cmd &")
or you could use fork as documented in the section on "fork" in the
perlfunc manpage, with further examples in the perlipc manpage. Some
things to be aware of, if you're on a Unix-like system:
STDIN, STDOUT and STDERR are shared
Both the main process and the backgrounded one (the "child"
process) share the same STDIN, STDOUT and STDERR filehandles. If
both try to access them at once, strange things can happen. You
may want to close or reopen these for the child. You can get
around this with `open'ing a pipe (see the section on "open" in
the perlfunc manpage) but on some systems this means that the
child process cannot outlive the parent.
Signals
You'll have to catch the SIGCHLD signal, and possibly SIGPIPE too.
SIGCHLD is sent when the backgrounded process finishes. SIGPIPE is
sent when you write to a filehandle whose child process has closed
(an untrapped SIGPIPE can cause your program to silently die).
This is not an issue with `system("cmd&")'.
Zombies
You have to be prepared to "reap" the child process when it
finishes
$SIG{CHLD} = sub { wait };
See the section on "Signals" in the perlipc manpage for other
examples of code to do this. Zombies are not an issue with
`system("prog &")'.
How do I trap control characters/signals?
You don't actually "trap" a control character. Instead, that character
generates a signal, which you then trap. Signals are documented in the
section on "Signals" in the perlipc manpage 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 the section on "Signals" in the perlipc manpage or chapter
6 of the Camel.
How do I modify the shadow password file on a Unix system?
If perl was installed correctly, the getpw*() functions described in
the perlfunc manpage provide (read-only) access to the shadow password
file. To change the file, make a new shadow password file (the format
varies from system to system - see the passwd(5) manpage for
specifics) and use pwd_mkdb(8) to install it (see the pwd_mkdb(5)
manpage for more details).
How do I set the time and date?
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";
How can I sleep() or alarm() for under a second?
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 the section on "select" in the perlfunc manpage. 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 .
How can I measure time under a second?
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 you 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] );
How can I do an atexit() or setjmp()/longjmp()? (Exception handling)
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). It
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 the section on "Signals" in the perlipc manpage 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.
Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean?
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.
How can I call my system's unique C functions from Perl?
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.
Where do I get the include files to do ioctl() or syscall()?
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 the
ExtUtils::MakeMaker manpage for more information (in brief, just use
make perl instead of a plain make to rebuild perl with a new static
extension).
Why do setuid perl scripts complain about kernel problems?
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.
How can I open a pipe both to and from a command?
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 the IPC::Open2 manpage).
Why can't I get the output of a command with system()?
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 8 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`;
How can I capture STDERR from an external command?
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 .
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 the IPC::Open3 manpage).
Why doesn't open() return an error when a pipe open fails?
It does, but probably not how you expect it to. On systems that follow
the standard fork()/exec() paradigm (eg, 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.
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 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.
How can I call backticks without shell processing?
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.
Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)?
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:
1 Try keeping around the seekpointer and go there, like this:
$where = tell(LOG);
seek(LOG, $where, 0);
2 If that doesn't work, try seeking to a different part of the file and
then back.
3 If that doesn't work, try seeking to a different part of the file,
reading something, and then seeking back.
4 If that doesn't work, give up on your stdio package and use sysread.
How can I convert my shell script to perl?
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.
Can I use perl to run a telnet or ftp session?
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;
How can I write expect in Perl?
Once upon a time, there was a library called chat2.pl (part of the
standard perl distribution), which never really got finished. These
days, your best bet is to look at the Comm.pl library available from
CPAN.
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 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]";
I {changed directory, modified my environment} in a perl script. How come the change disappeared when I exited the script? How do I get my changes to be visible?
Unix
In the strictest sense, it can't be done -- the script executes as
a different process from the shell it was started from. Changes to
a process are not reflected in its parent, only in its own
children created after the change. There is shell magic that may
allow you to fake it by eval()ing the script's output in your
shell; check out the comp.unix.questions FAQ for details.
VMS Change to %ENV persist after Perl exits, but directory changes do not.
How do I close a process's filehandle without waiting for it to complete?
Assuming your system supports such things, just send an appropriate
signal to the process (see the section on "kill" in the perlfunc
manpage. It's common to first send a TERM signal, wait a little bit,
and then send a KILL signal to finish it off.
How do I fork a daemon process?
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 the tty(4)
manpage for details.
* Change directory to /
* Reopen STDIN, STDOUT, and STDERR so they're not connected to the old
tty.
* Background yourself like this:
fork && exit;
How do I make my program run with sh and csh?
See the eg/nih script (part of the perl source distribution).
How do I find out if I'm running interactively or not?
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";
}
How do I timeout a slow event?
Use the alarm() function, probably in conjunction with a signal
handler, as documented the section on "Signals" in the perlipc manpage
and chapter 6 of the Camel. You may instead use the more flexible
Sys::AlarmCall module available from CPAN.
How do I set CPU limits?
Use the BSD::Resource module from CPAN.
How do I avoid zombies on a Unix system?
Use the reaper code from the section on "Signals" in the perlipc
manpage to call wait() when a SIGCHLD is received, or else use the
double-fork technique described in the "fork" entry in the perlfunc
manpage.
How do I use an SQL database?
There are a number of excellent interfaces to SQL databases. See the
DBD::* modules available from
http://www.perl.com/CPAN/modules/dbperl/DBD .
How do I make a system() exit on control-C?
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.
How do I open a file without blocking?
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: $!":
How do I install a CPAN module?
The easiest way is to have the CPAN module do it for you. This module
comes with perl version 5.004 and later. To manually install the CPAN
module, or any well-behaved CPAN module for that matter, follow these
steps:
1 Unpack the source into a temporary area.
2 perl Makefile.PL
3 make
4 make test
5 make install
If your version of perl is compiled without dynamic loading, then you
just need to replace step 3 (make) with make perl and you will get a
new perl binary with your extension linked in.
See the ExtUtils::MakeMaker manpage for more details on building
extensions, the question "How do I keep my own module/library
directory?"
How do I keep my own module/library directory?
When you build modules, use the PREFIX option when generating
Makefiles:
perl Makefile.PL PREFIX=/u/mydir/perl
then either set the PERL5LIB environment variable before you run
scripts that use the modules/libraries (see the perlrun manpage) or
say
use lib '/u/mydir/perl';
See Perl's the lib manpage for more information.
How do I add the directory my program lives in to the module/library search path?
use FindBin;
use lib "$FindBin:Bin";
use your_own_modules;
How do I add a directory to my include path at runtime?
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.
How do I get one key from the terminal at a time, under POSIX?
#!/usr/bin/perl -w
use strict;
$| = 1;
for (1..4) {
my $got;
print "gimme: ";
$got = getone();
print "--> $got\n";
}
exit;
BEGIN {
use POSIX qw(:termios_h);
my ($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);
$term->setcc(VTIME, 1);
$term->setattr($fd_stdin, TCSANOW);
}
sub cooked {
$term->setlflag($oterm);
$term->setcc(VTIME, 0);
$term->setattr($fd_stdin, TCSANOW);
}
sub getone {
my $key = '';
cbreak();
sysread(STDIN, $key, 1);
cooked();
return $key;
}
}
END { cooked() }
AUTHOR AND COPYRIGHT
Copyright (c) 1997 Tom Christiansen and Nathan Torkington. All rights
reserved. See the perlfaq manpage for distribution information.
--
Tom Christiansen tchrist@jhereg.perl.com
_doprnt(pat, args, &fakebuf); /* what a kludge */
--Larry Wall, from util.c in the v5.0 perl distribution
------------------------------
Date: 4 May 1997 22:01:41 GMT
From: PerlFAQ <perlfaq-suggestions@mox.perl.com>
Subject: Perl FAQ part 9 of 0..9: Networking [Periodic Posting]
Message-Id: <5kj105$9pa$1@csnews.cs.colorado.edu>
NAME
perlfaq9 - Networking
($Revision: 1.16 $, $Date: 1997/04/23 18:12:06 $)
DESCRIPTION
This section deals with questions related to networking, the internet,
and a few on the web.
My CGI script runs from the command line but not the browser. Can you help me fix it?
Sure, but you probably can't afford our contracting rates :-)
Seriously, if you can demonstrate that you've read the following FAQs
and that your problem isn't something simple that can be easily
answered, you'll probably receive a courteous and useful reply to your
question if you post it on comp.infosystems.www.authoring.cgi (if it's
something to do with HTTP, HTML, or the CGI protocols). Questions that
appear to be Perl questions but are really CGI ones that are posted to
comp.lang.perl.misc may not be so well received.
The useful FAQs are:
http://www.perl.com/perl/faq/idiots-guide.html
http://www3.pair.com/webthing/docs/cgi/faqs/cgifaq.shtml
http://www.perl.com/perl/faq/perl-cgi-faq.html
http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html
http://www.boutell.com/faq/
How do I remove HTML from a string?
The most correct way (albeit not the fastest) is to use HTML::Parse
from CPAN (part of the libwww-perl distribution, which is a must-have
module for all web hackers).
Many folks attempt a simple-minded regular expression approach, like
`s/<.*?>//g', but that fails in many cases because the tags may
continue over line breaks, they may contain quoted angle-brackets, or
HTML comment may be present. Plus folks forget to convert entities,
like `<' for example.
Here's one "simple-minded" approach, that works for most files:
#!/usr/bin/perl -p0777
s/<(?:[^>'"]*|(['"]).*?\1)*>//gs
If you want a more complete solution, see the 3-stage striphtml
program in
http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/striphtml.gz
.
How do I extract URLs?
A quick but imperfect approach is
#!/usr/bin/perl -n00
# qxurl - tchrist@perl.com
print "$2\n" while m{
< \s*
A \s+ HREF \s* = \s* (["']) (.*?) \1
\s* >
}gsix;
This version does not adjust relative URLs, understand alternate
bases, deal with HTML comments, deal with HREF and NAME attributes in
the same tag, or accept URLs themselves as arguments. It also runs
about 100x faster than a more "complete" solution using the LWP suite
of modules, such as the
http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/xurl.gz
program.
How do I download a file from the user's machine? How do I open a file on another machine?
In the context of an HTML form, you can use what's known as
multipart/form-data encoding. The CGI.pm module (available from CPAN)
supports this in the start_multipart_form() method, which isn't the
same as the startform() method.
How do I make a pop-up menu in HTML?
Use the <SELECT> and <OPTION> tags. The CGI.pm module (available from
CPAN) supports this widget, as well as many others, including some
that it cleverly synthesizes on its own.
How do I fetch an HTML file?
One approach, if you have the lynx text-based HTML browser installed
on your system, is this:
$html_code = `lynx -source $url`;
$text_data = `lynx -dump $url`;
The libwww-perl (LWP) modules from CPAN provide a more powerful way to
do this. They work through proxies, and don't require lynx:
# print HTML from a URL
use LWP::Simple;
getprint "http://www.sn.no/libwww-perl/";
# print ASCII from HTML from a URL
use LWP::Simple;
use HTML::Parse;
use HTML::FormatText;
my ($html, $ascii);
$html = get("http://www.perl.com/");
defined $html
or die "Can't fetch HTML from http://www.perl.com/";
$ascii = HTML::FormatText->new->format(parse_html($html));
print $ascii;
how do I decode or create those %-encodings on the web?
Here's an example of decoding:
$string = "http://altavista.digital.com/cgi-bin/query?pg=q&what=news&fmt=.&q=%2Bcgi-bin+%2Bperl.exe";
$string =~ s/%([a-fA-F0-9]{2})/chr(hex($1))/ge;
Encoding is a bit harder, because you can't just blindly change all
the non-alphanumunder character (`\W') into their hex escapes. It's
important that characters with special meaning like `/' and `?' *not*
be translated. Probably the easiest way to get this right is to avoid
reinventing the wheel and just use the URI::Escape module, which is
part of the libwww-perl package (LWP) available from CPAN.
How do I redirect to another page?
Instead of sending back a `Content-Type' as the headers of your reply,
send back a `Location:' header. Officially this should be a `URI:'
header, so the CGI.pm module (available from CPAN) sends back both:
Location: http://www.domain.com/newpage
URI: http://www.domain.com/newpage
Note that relative URLs in these headers can cause strange effects
because of "optimizations" that servers do.
How do I put a password on my web pages?
That depends. You'll need to read the documentation for your web
server, or perhaps check some of the other FAQs referenced above.
How do I edit my .htpasswd and .htgroup files with Perl?
The HTTPD::UserAdmin and HTTPD::GroupAdmin modules provide a
consistent OO interface to these files, regardless of how they're
stored. Databases may be text, dbm, Berkley DB or any database with a
DBI compatible driver. HTTPD::UserAdmin supports files used by the
`Basic' and `Digest' authentication schemes. Here's an example:
use HTTPD::UserAdmin ();
HTTPD::UserAdmin
->new(DB => "/foo/.htpasswd")
->add($username => $password);
How do I make sure users can't enter values into a form that cause my CGI script to do bad things?
Read the CGI security FAQ, at http://www-
genome.wi.mit.edu/WWW/faqs/www-security-faq.html, and the Perl/CGI FAQ
at http://www.perl.com/CPAN/doc/FAQs/cgi/perl-cgi-faq.html.
In brief: use tainting (see the perlsec manpage), which makes sure
that data from outside your script (eg, CGI parameters) are never used
in `eval' or `system' calls. In addition to tainting, never use the
single-argument form of system() or exec(). Instead, supply the
command and arguments as a list, which prevents shell globbing.
How do I parse an email header?
For a quick-and-dirty solution, try this solution derived from page
222 of the 2nd edition of "Programming Perl":
$/ = '';
$header = <MSG>;
$header =~ s/\n\s+/ /g; # merge continuation lines
%head = ( UNIX_FROM_LINE, split /^([-\w]+):\s*/m, $header );
That solution doesn't do well if, for example, you're trying to
maintain all the Received lines. A more complete approach is to use
the Mail::Header module from CPAN (part of the MailTools package).
How do I decode a CGI form?
A lot of people are tempted to code this up themselves, so you've
probably all seen a lot of code involving `$ENV{CONTENT_LENGTH}' and
`$ENV{QUERY_STRING}'. It's true that this can work, but there are also
a lot of versions of this floating around that are quite simply
broken!
Please do not be tempted to reinvent the wheel. Instead, use the
CGI.pm or CGI_Lite.pm (available from CPAN), or if you're trapped in
the module-free land of perl1 .. perl4, you might look into cgi-lib.pl
(available from http://www.bio.cam.ac.uk/web/form.html).
How do I check a valid email address?
You can't.
Without sending mail to the address and seeing whether it bounces (and
even then you face the halting problem), you cannot determine whether
an email address is valid. Even if you apply the email header
standard, you can have problems, because there are deliverable
addresses that aren't RFC-822 (the mail header standard) compliant,
and addresses that aren't deliverable which are compliant.
Many are tempted to try to eliminate many frequently-invalid email
addresses with a simple regexp, such as `/^[\w.-]+\@([\w.-]\.)+\w+$/'.
However, this also throws out many valid ones, and says nothing about
potential deliverability, so is not suggested. Instead, see
http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/ckaddr.gz ,
which actually checks against the full RFC spec (except for nested
comments), looks for addresses you may not wish to accept email to
(say, Bill Clinton or your postmaster), and then makes sure that the
hostname given can be looked up in DNS. It's not fast, but it works.
Here's an alternative strategy used by many CGI script authors: Check
the email address with a simple regexp (such as the one above). If the
regexp matched the address, accept the address. If the regexp didn't
match the address, request confirmation from the user that the email
address they entered was correct.
How do I decode a MIME/BASE64 string?
The MIME-tools package (available from CPAN) handles this and a lot
more. Decoding BASE64 becomes as simple as:
use MIME::base64;
$decoded = decode_base64($encoded);
A more direct approach is to use the unpack() function's "u" format
after minor transliterations:
tr#A-Za-z0-9+/##cd; # remove non-base64 chars
tr#A-Za-z0-9+/# -_#; # convert to uuencoded format
$len = pack("c", 32 + 0.75*length); # compute length byte
print unpack("u", $len . $_); # uudecode and print
How do I return the user's email address?
On systems that support getpwuid, the $< variable and the
Sys::Hostname module (which is part of the standard perl
distribution), you can probably try using something like this:
use Sys::Hostname;
$address = sprintf('%s@%s', getpwuid($<), hostname);
Company policies on email address can mean that this generates
addresses that the company's email system will not accept, so you
should ask for users' email addresses when this matters. Furthermore,
not all systems on which Perl runs are so forthcoming with this
information as is Unix.
The Mail::Util module from CPAN (part of the MailTools package)
provides a mailaddress() function that tries to guess the mail address
of the user. It makes a more intelligent guess than the code above,
using information given when the module was installed, but it could
still be incorrect. Again, the best way is often just to ask the user.
How do I send/read mail?
Sending mail: the Mail::Mailer module from CPAN (part of the MailTools
package) is UNIX-centric, while Mail::Internet uses Net::SMTP which is
not UNIX-centric. Reading mail: use the Mail::Folder module from CPAN
(part of the MailFolder package) or the Mail::Internet module from
CPAN (also part of the MailTools package).
# sending mail
use Mail::Internet;
use Mail::Header;
# say which mail host to use
$ENV{SMTPHOSTS} = 'mail.frii.com';
# create headers
$header = new Mail::Header;
$header->add('From', 'gnat@frii.com');
$header->add('Subject', 'Testing');
$header->add('To', 'gnat@frii.com');
# create body
$body = 'This is a test, ignore';
# create mail object
$mail = new Mail::Internet(undef, Header => $header, Body => \[$body]);
# send it
$mail->smtpsend or die;
How do I find out my hostname/domainname/IP address?
A lot of code has historically cavalierly called the ``hostname`'
program. While sometimes expedient, this isn't very portable. It's one
of those tradeoffs of convenience versus portability.
The Sys::Hostname module (part of the standard perl distribution) will
give you the hostname after which you can find out the IP address
(assuming you have working DNS) with a gethostbyname() call.
use Socket;
use Sys::Hostname;
my $host = hostname();
my $addr = inet_ntoa(scalar(gethostbyname($name)) || 'localhost');
Probably the simplest way to learn your DNS domain name is to grok it
out of /etc/resolv.conf, at least under Unix. Of course, this assumes
several things about your resolv.conf configuration, including that it
exists.
(We still need a good DNS domain name-learning method for non-Unix
systems.)
How do I fetch a news article or the active newsgroups?
Use the Net::NNTP or News::NNTPClient modules, both available from
CPAN. This can make tasks like fetching the newsgroup list as simple
as:
perl -MNews::NNTPClient
-e 'print News::NNTPClient->new->list("newsgroups")'
How do I fetch/put an FTP file?
LWP::Simple (available from CPAN) can fetch but not put. Net::FTP
(also available from CPAN) is more complex but can put as well as
fetch.
How can I do RPC in Perl?
A DCE::RPC module is being developed (but is not yet available), and
will be released as part of the DCE-Perl package (available from
CPAN). No ONC::RPC module is known.
AUTHOR AND COPYRIGHT
Copyright (c) 1997 Tom Christiansen and Nathan Torkington. All rights
reserved. See the perlfaq manpage for distribution information.
--
Tom Christiansen tchrist@jhereg.perl.com
"There is no reason for any individual to have a computer in their
home." (Ken Olson, President, Digital Equipment, 1977)
------------------------------
Date: Sun, 04 May 1997 22:49:05 -0400
From: Peter <peter@webcanada.com>
Subject: Perl on Win95?
Message-Id: <336D4AA1.37F5@webcanada.com>
Hello..
I'm trying to see if I can install PERL to run under Windows 95...
I would like to correspond with people who have experience installing
it, particularily to help *with* the install (ie. how to do it<G>) and
any small problems that may come up.
Appreciate all e-mail replies (peter@webcanada.com).
Thanks,
Peter.
------------------------------
Date: 8 Mar 97 21:33:47 GMT (Last modified)
From: Perl-Request@ruby.oce.orst.edu (Perl-Users-Digest Admin)
Subject: Digest Administrivia (Last modified: 8 Mar 97)
Message-Id: <null>
Administrivia:
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The Meta-FAQ, an article containing information about the FAQ, is
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------------------------------
End of Perl-Users Digest V8 Issue 429
*************************************
