MAN page from Old RedHat 5.X perl-5.004-4.i386.rpm
PERLFAQ8
Section: Perl Programmers Reference Guide (1)
Updated: perl 5.004, patch 04
Index NAME
perlfaq8 - System Interaction ($Revision: 1.21 $,
$Date: 1997/04/24 22:44:19 $)
DESCRIPTION
This section of the Perl FAQ covers questions involving operatingsystem interaction. This involves interprocess communication (IPC),control over the user-interface (keyboard, screen and pointingdevices), and most anything else not related to data manipulation.
Read the FAQs and documentation specific to the port of perl to youroperating system (eg, the perlvms manpage, the perlplan9 manpage, ...). These shouldcontain 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 operatingsystem that your perl binary was built for.
How come exec() doesn't return?
Because that's what it does: it replaces your currently runningprogram with a different one. If you want to keep going (as isprobably 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 putthe terminal into ``no echo'' mode, then just read the passwordnormally. You may do this with an old-style ioctl() function, POSIXterminal control (see the POSIX manpage, and Chapter 7 of the Camel), or a callto the stty program, with varying degrees of portability.
You can also do this for most systems using the Term::ReadKey modulefrom 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. Inthe 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 thefollowing
- lockfiles
- Your system may use lockfiles to control multiple access. Make sureyou follow the correct protocol. Unpredictable behaviour can resultfrom 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 fordetails). You may wish to open it without running the risk ofblocking by using sysopen() and O_RDWR|O_NDELAY|O_NOCTTY from theFcntl module (part of the standard perl distribution). Seethe 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 ratherthan a ``\n''. In some ports of perl, ``\r'' and ``\n'' are different fromtheir usual (Unix) ASCII values of ``\012'' and ``\015''. You may have togive 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 isstill no unified scheme for terminating a line that is portablebetween Unix, DOS/Win, and Macintosh, except to terminate ALL lineends with ``\015\012'', and strip what you don't need from the output.This applies especially to socket I/O and autoflushing, discussednext.
- 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 usingsocket I/O between Unix and Macintosh. You'll need to hardcode yourline terminators, in that case.
- non-blocking input
- If you are doing a blocking read() or sysread(), you'll have toarrange for an alarm handler to provide a timeout (seethe alarm entry in the perlfunc manpage). If you have a non-blocking open, you'll likelyhave a non-blocking read, which means you may have to use a 4-argselect() to determine whether I/O is ready on that device (seethe 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 isbound to get you talked about.
Seriously, you can't if they are Unix password files - the Unixpassword system employs one-way encryption. Programs like Crack canforcibly (and intelligently) try to guess passwords, but don't (can't)guarantee quick success.
If you're worried about users selecting bad passwords, you shouldproactively check when they try to change their password (by modifyingpasswd(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, withfurther examples in the
perlipc manpage. Some things to be aware of, if you'reon 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 toaccess them at once, strange things can happen. You may want to closeor reopen these for the child. You can get around this withopening a pipe (see the section on open in the perlfunc manpage) but on some systems thismeans 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 issent when you write to a filehandle whose child process has closed (anuntrapped SIGPIPE can cause your program to silently die). This isnot 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, thatcharacter generates a signal, which you then trap. Signals aredocumented 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 youattempt to print() in a handler that got invoked during another stdiooperation your internal structures will likely be in aninconsistent state, and your program will dump core. You cansometimes avoid this by using syswrite() instead of print().
Unless you're exceedingly careful, the only safe things to do inside asignal 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 notcalled (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 ifyou'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 ablocking
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 inthe
perlfunc manpage provide (read-only) access to the shadow password file.To change the file, make a new shadow password file (the format variesfrom 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 beable 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-processbasis.) 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 canprobably 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 asdocumented 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 (availablefrom
CPAN) provides this functionality for some systems.
In general, you may not be able to. But if you system supports both thesyscall() 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 orthread ends (see the
perlmod manpage manpage for more details). It isn'tcalled 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 canuse
eval() as setjmp and
die() as longjmp. For details of this, seethe 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 theexceptions.pl library (part of the standard perl distribution).
If you want the atexit() syntax (and an rmexit() as well), try theAtExit 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 thestandard socket constants. Since these were constant across allarchitectures, they were often hardwired into perl code. The properway to deal with this is to ``use Socket'' to get the correct values.
Note that even though SunOS and Solaris are binary compatible, thesevalues 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 answerto ``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 inthe
perlfunc manpage).
Remember to check the modules that came with your distribution, andCPAN 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 thestandard perl distribution. This program converts
cpp(1) directivesin 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 andsanity you probably ought to use h2xs (also part of the standard perldistribution). 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 probablyought to use h2xs. See the perlxstut manpage and the ExtUtils::MakeMaker manpage formore information (in brief, just use make perl instead of a plainmake 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 setuidscripts 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 aneasy-to-use approach that internally uses
pipe(),
fork(), and
exec()to do the job. Make sure you read the deadlock warnings in itsdocumentation, 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, andthe high 8 bits are the actual exit value). Backticks (``) run acommand 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 thescript'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 aduplicate of
STDOUT:
$output = `$cmd 2>&1`; open (PIPE, "cmd 2>&1 |");
Note that you
cannot simply open
STDERR to be a dup of
STDOUTin 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 wasgoing at the time of the
open(). The backticks then make
STDOUT go toa string, but don't change
STDERR (which still goes to the old
STDOUT).
Note that you must use Bourne shell (sh(1)) redirection syntax inbackticks, not csh(1)! Details on why Perl's system() and backtickand pipe opens all use the Bourne shell are inhttp://www.perl.com/CPAN/doc/FMTEYEWTK/versus/csh.whynot .
You may also use the IPC::Open3 module (part of the standard perldistribution), but be warned that it has a different order ofarguments 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 thatfollow the standard
fork()/
exec() paradigm (eg, Unix), it works likethis:
open() causes a
fork(). In the parent,
open() returns with theprocess
ID of the child. The child
exec()s the command to be pipedto/from. The parent can't know whether the
exec() was successful ornot - all it can return is whether the
fork() succeeded or not. Tofind out if the command succeeded, you have to catch
SIGCHLD and
wait() to get the exit status. You should also catch
SIGPIPE ifyou'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 whatyou expect - unless perl uses a shell to start your command. In thiscase 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 goodway to write maintainable code because backticks have a (potentiallyhumungous) return value, and you're ignoring it. It's may also not be veryefficient, because you have to read in all the lines of output, allocatememory for them, and then throw it away. Too often people are lulledto 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
$? to see whetherthe program even ran correctly. Even if you wrote
print `cat /etc/termcap`;
In most cases, this could and probably should be written as
system("cat /etc/termcap") == 0 or die "cat program failed!";Which will get the output quickly (as its generated, instead of onlyat the end ) and also check the return value.
system() also provides direct control over whether shell wildcardprocessing may take place, whereas backticks do not.
How can I call backticks without shell processing?
This is a bit tricky. Instead of writing
@ok = `grep @opts '$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 thetechnically correct way to do it. Here are some less reliableworkarounds:
- 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 andthen back.
- 3
- If that doesn't work, try seeking to a different part ofthe 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, andthis very awkwardness is what would make a shell->perl converternigh-on impossible to write. By rewriting it, you'll think about whatyou're really trying to do, and hopefully will escape the shell'spipeline 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.sharwill also help for emulating the telnet protocol, but Net::Telnet isquite probably easier to use..
If all you want to do is pretend to be telnet but don't needthe initial telnet handshaking, then the standard dual-processapproach 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 thestandard perl distribution), which never really got finished. Thesedays, 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 (toavoid people seeing passwords, for example) then you should rewriteyour program so that critical information is never given as anargument. Hiding the arguments won't make your program completelysecure.
To actually alter the visible command line, you can assign to thevariable $0 as documented in the perlvar manpage. This won't work on alloperating systems, though. Daemon programs like sendmail place theirstate 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 adifferent process from the shell it was started from. Changes to aprocess are not reflected in its parent, only in its own childrencreated after the change. There is shell magic that may allow you tofake it by eval()ing the script's output in your shell; check out thecomp.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 signalto the process (see the section on
kill in the
perlfunc manpage. It's common to first send a
TERMsignal, 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 fromits tty), then the following process is reported to work on mostUnixish systems. Non-Unix users should check their Your_OS::Processmodule for other solutions.
- *
- Open /dev/tty and use the the TIOCNOTTY ioctl on it. See the tty(4) manpagefor details.
- *
- Change directory to /
- *
- Reopen STDIN, STDOUT, and STDERR so they're not connected to the oldtty.
- *
- 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 matchesthe 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 signalhandler, as documented the section on
Signals in the
perlipc manpage and chapter 6 of theCamel. You may instead use the more flexible Sys::AlarmCall moduleavailable 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 describedin 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 forsample code) and then have a signal handler for the
INT signal thatpasses 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 supportsnon-blocking reads (most Unixish systems do), you need only to use theO_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: $!":
How do I install a CPAN module?
The easiest way is to have the
CPAN module do it for you. This modulecomes with perl version 5.004 and later. To manually install the
CPANmodule, or any well-behaved
CPAN module for that matter, follow thesesteps:
- 1
- Unpack the source into a temporary area.
- 2
perl Makefile.PL
- 3
make
- 4
make test
- 5
make install
If your version of perl is compiled without dynamic loading, then youjust need to replace step 3 (make) with make perl and you willget a new perl binary with your extension linked in.
See the ExtUtils::MakeMaker manpage for more details on building extensions,the question ``How do I keep my own module/library directory?''
How do I keep my own module/library directory?
When you build modules, use the
PREFIX option when generatingMakefiles:
perl Makefile.PL PREFIX=/u/mydir/perl
then either set the
PERL5LIB environment variable before you runscripts that use the modules/libraries (see the
perlrun manpage) or say
use lib '/u/mydir/perl';
See Perl's the
lib manpage for more information.
How do I add the directory my program lives in to the module/library search path?
use FindBin; use lib "$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 machinedependent architectures. The lib.pm pragmatic module was firstincluded 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.
Index
- NAME
- DESCRIPTION
- How do I find out which operating system I'm running under?
- How come exec() doesn't return?
- How do I do fancy stuff with the keyboard/screen/mouse?
- How do I ask the user for a password?
- How do I read and write the serial port?
- How do I decode encrypted password files?
- How do I start a process in the background?
- How do I trap control characters/signals?
- How do I modify the shadow password file on a Unix system?
- How do I set the time and date?
- How can I sleep() or alarm() for under a second?
- How can I measure time under a second?
- How can I do an atexit() or setjmp()/longjmp()? (Exception handling)
- Why doesn't my sockets program work under System V (Solaris)? What does the error message Protocol not supported mean?
- How can I call my system's unique C functions from Perl?
- Where do I get the include files to do ioctl() or syscall()?
- Why do setuid perl scripts complain about kernel problems?
- How can I open a pipe both to and from a command?
- Why can't I get the output of a command with system()?
- How can I capture STDERR from an external command?
- Why doesn't open() return an error when a pipe open fails?
- What's wrong with using backticks in a void context?
- How can I call backticks without shell processing?
- Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)?
- How can I convert my shell script to perl?
- Can I use perl to run a telnet or ftp session?
- How can I write expect in Perl?
- Is there a way to hide perl's command line from programs such as ps?
- 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?
- How do I close a process's filehandle without waiting for it to complete?
- How do I fork a daemon process?
- How do I make my program run with sh and csh?
- How do I find out if I'm running interactively or not?
- How do I timeout a slow event?
- How do I set CPU limits?
- How do I avoid zombies on a Unix system?
- How do I use an SQL database?
- How do I make a system() exit on control-C?
- How do I open a file without blocking?
- How do I install a CPAN module?
- How do I keep my own module/library directory?
- How do I add the directory my program lives in to the module/library search path?
- How do I add a directory to my include path at runtime?
- How do I get one key from the terminal at a time, under POSIX?
- AUTHOR AND COPYRIGHT
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