perlfaq8

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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 opening 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.

       o   Open /dev/tty and use the the TIOCNOTTY ioctl on it.
           See the tty(4) manpage for details.

       o   Change directory to /

       o   Reopen STDIN, STDOUT, and STDERR so they're not
           connected to the old tty.


       o   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.
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