PERLFAQ8(1)
NNAAMMEE
perlfaq8 - System Interaction ($Revision: 1.21 $, $Date:
1997/04/24 22:44:19 $)
DDEESSCCRRIIPPTTIIOONN
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.
HHooww ddoo II ffiinndd oouutt wwhhiicchh ooppeerraattiinngg ssyysstteemm II''mm rruunnnniinngg
uunnddeerr??
The $^O variable ($OSTYPE if you use English) contains the
operating system that your perl binary was built for.
HHooww ccoommee 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.
HHooww ddoo II ddoo ffaannccyy ssttuuffff wwiitthh tthhee kkeeyybbooaarrdd//ssccrreeeenn//mmoouussee??
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
HHooww ddoo II aasskk tthhee uusseerr ffoorr aa ppaasssswwoorrdd??
(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 ssttttyy 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.
HHooww ddoo II rreeaadd aanndd wwrriittee tthhee sseerriiaall ppoorrtt??
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.
HHooww ddoo II ddeeccooddee eennccrryypptteedd ppaasssswwoorrdd ffiilleess??
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).
HHooww ddoo II ssttaarrtt aa pprroocceessss iinn tthhee bbaacckkggrroouunndd??
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 &").
HHooww ddoo II ttrraapp ccoonnttrrooll cchhaarraacctteerrss//ssiiggnnaallss??
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.
HHooww ddoo II mmooddiiffyy tthhee sshhaaddooww ppaasssswwoorrdd ffiillee oonn aa UUnniixx ssyysstteemm??
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).
HHooww ddoo II sseett tthhee ttiimmee aanndd ddaattee??
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";
HHooww ccaann II 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
.
HHooww ccaann II mmeeaassuurree ttiimmee uunnddeerr aa sseeccoonndd??
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] );
HHooww ccaann II ddoo aann 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.
WWhhyy ddooeessnn''tt mmyy ssoocckkeettss pprrooggrraamm wwoorrkk uunnddeerr SSyysstteemm VV
((SSoollaarriiss))?? WWhhaatt ddooeess tthhee eerrrroorr mmeessssaaggee """"PPrroottooccooll nnoott
ssuuppppoorrtteedd"""" mmeeaann??
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.
HHooww ccaann II ccaallll mmyy ssyysstteemm''ss uunniiqquuee CC ffuunnccttiioonnss ffrroomm PPeerrll??
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.
WWhheerree ddoo II ggeett tthhee iinncclluuddee ffiilleess ttoo ddoo 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 mmaakkee ppeerrll instead of a plain mmaakkee to
rebuild perl with a new static extension).
WWhhyy ddoo sseettuuiidd ppeerrll ssccrriippttss ccoommppllaaiinn aabboouutt kkeerrnneell pprroobblleemmss??
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.
HHooww ccaann II ooppeenn aa ppiippee bbootthh ttoo aanndd ffrroomm aa ccoommmmaanndd??
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).
WWhhyy ccaann''tt II ggeett tthhee oouuttppuutt ooff aa ccoommmmaanndd wwiitthh 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`;
HHooww ccaann II ccaappttuurree SSTTDDEERRRR ffrroomm aann eexxtteerrnnaall ccoommmmaanndd??
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 oonnllyy
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).
WWhhyy ddooeessnn''tt 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.
WWhhaatt''ss wwrroonngg wwiitthh uussiinngg bbaacckkttiicckkss iinn aa vvooiidd ccoonntteexxtt??
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 $? to see whether the program even ran correctly.
Even if you wrote
print `cat /etc/termcap`;
In most cases, this could and probably should be written
as
system("cat /etc/termcap") == 0
or die "cat program failed!";
Which will get the output quickly (as its generated,
instead of only at the end ) and also check the return
value.
system() also provides direct control over whether shell
wildcard processing may take place, whereas backticks do
not.
HHooww ccaann II ccaallll bbaacckkttiicckkss wwiitthhoouutt sshheellll pprroocceessssiinngg??
This is a bit tricky. Instead of writing
@ok = `grep @opts '$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.
WWhhyy ccaann''tt mmyy ssccrriipptt rreeaadd ffrroomm SSTTDDIINN aafftteerr II ggaavvee iitt EEOOFF
((^^DD oonn UUnniixx,, ^^ZZ oonn MMSS--DDOOSS))??
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.
HHooww ccaann II ccoonnvveerrtt mmyy sshheellll ssccrriipptt ttoo ppeerrll??
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.
CCaann II uussee ppeerrll ttoo rruunn aa tteellnneett oorr ffttpp sseessssiioonn??
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;
HHooww ccaann II wwrriittee eexxppeecctt iinn PPeerrll??
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.
IIss tthheerree aa wwaayy ttoo hhiiddee ppeerrll''ss ccoommmmaanndd lliinnee ffrroomm pprrooggrraammss
ssuucchh aass """"ppss""""??
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]";
II {{cchhaannggeedd ddiirreeccttoorryy,, mmooddiiffiieedd mmyy eennvviirroonnmmeenntt}} iinn aa ppeerrll
ssccrriipptt.. HHooww ccoommee tthhee cchhaannggee ddiissaappppeeaarreedd wwhheenn II eexxiitteedd tthhee
ssccrriipptt?? HHooww ddoo II ggeett mmyy cchhaannggeess ttoo bbee vviissiibbllee??
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.
HHooww ddoo II cclloossee aa pprroocceessss''ss ffiilleehhaannddllee wwiitthhoouutt wwaaiittiinngg ffoorr
iitt ttoo ccoommpplleettee??
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.
HHooww ddoo II ffoorrkk aa ddaaeemmoonn pprroocceessss??
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;
HHooww ddoo II mmaakkee mmyy pprrooggrraamm rruunn wwiitthh sshh aanndd ccsshh??
See the eg/nih script (part of the perl source
distribution).
HHooww ddoo II ffiinndd oouutt iiff II''mm rruunnnniinngg iinntteerraaccttiivveellyy oorr nnoott??
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";
}
HHooww ddoo II ttiimmeeoouutt aa ssllooww eevveenntt??
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.
HHooww ddoo II sseett CCPPUU lliimmiittss??
Use the BSD::Resource module from CPAN.
HHooww ddoo II aavvooiidd zzoommbbiieess oonn aa UUnniixx ssyysstteemm??
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.
HHooww ddoo II uussee aann SSQQLL ddaattaabbaassee??
There are a number of excellent interfaces to SQL
databases. See the DBD::* modules available from
http://www.perl.com/CPAN/modules/dbperl/DBD .
HHooww ddoo II mmaakkee aa 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.
HHooww ddoo II ooppeenn aa ffiillee wwiitthhoouutt bblloocckkiinngg??
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: $!":
HHooww ddoo II iinnssttaallll aa CCPPAANN mmoodduullee??
The easiest way is to have the CPAN module do it for you.
This module comes with perl version 5.004 and later. To
manually install the CPAN module, or any well-behaved CPAN
module for that matter, follow these steps:
1 Unpack the source into a temporary area.
2
perl Makefile.PL
3
make
4
make test
5
make install
If your version of perl is compiled without dynamic
loading, then you just need to replace step 3 (mmaakkee) with
mmaakkee ppeerrll and you will get a new perl binary with your
extension linked in.
See the ExtUtils::MakeMaker manpage for more details on
building extensions, the question "How do I keep my own
module/library directory?"
HHooww ddoo II kkeeeepp mmyy oowwnn mmoodduullee//lliibbrraarryy ddiirreeccttoorryy??
When you build modules, use the PREFIX option when
generating Makefiles:
perl Makefile.PL PREFIX=/u/mydir/perl
then either set the PERL5LIB environment variable before
you run scripts that use the modules/libraries (see the
perlrun manpage) or say
use lib '/u/mydir/perl';
See Perl's the lib manpage for more information.
HHooww ddoo II aadddd tthhee ddiirreeccttoorryy mmyy pprrooggrraamm lliivveess iinn ttoo tthhee
mmoodduullee//lliibbrraarryy sseeaarrcchh ppaatthh??
use FindBin;
use lib "$FindBin:Bin";
use your_own_modules;
HHooww ddoo II aadddd aa ddiirreeccttoorryy ttoo mmyy iinncclluuddee ppaatthh aatt rruunnttiimmee??
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.
HHooww ddoo II ggeett oonnee kkeeyy ffrroomm tthhee tteerrmmiinnaall aatt aa ttiimmee,, uunnddeerr PPOOSSIIXX??
#!/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() }
AAUUTTHHOORR AANNDD CCOOPPYYRRIIGGHHTT
Copyright (c) 1997 Tom Christiansen and Nathan Torkington.
All rights reserved. See the perlfaq manpage for
distribution information.