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 vagiaries of your perl.
Term::Cap Standard perl distribution
Term::ReadKey CPAN
Term::ReadLine::Gnu CPAN
Term::ReadLine::Perl CPAN
Term::Screen CPAN
Term::Cap Standard perl distribution
Curses CPAN
Term::ANSIColor CPAN
Tk CPAN
There's an example of this in in crypt). First, you put the terminal into ``no echo'' mode, then just read the password normally. You may do this with an old-style ioctl function, POSIX terminal control (see the POSIX manpage, and Chapter 7 of the Camel), or a call to the stty program, with varying degrees of portability.
You can also do this for most systems using the Term::ReadKey module from CPAN, which is easier to use and in theory more portable.
sysopen and O_RDWR|O_NDELAY|O_NOCTTY from the Fcntl module (part of the standard perl distribution). See
sysopen for more on this approach.
print DEV "atv1\012"; # wrong, for some devices
print DEV "atv1\015"; # right, for some devices
Even though with normal text files, a ``\n'' will do the trick, over the network, there is still no unified scheme for terminating a line that is cross-platform to all of 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.
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 $| and select):
$oldh = select(DEV);
$| = 1;
select($oldh);
You'll also see code that does this without a temporary variable, as in
select((select(DEV), $| = 1)[0]);
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.
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, for example).
system("cmd &")
or you could use fork as documented in fork, with further examples in the perlipc manpage. Some things to be aware of, if you're on a Unix-like system:
$SIG{CHLD} = sub { wait };
See Signals for other examples of code to do this. Zombies are not an issue with system.
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 in an inconsistent state, and your program will dump core. You can sometimes avoid this by using syswrite instead of print.
Unless you're exceedingly careful, the only safe things to do inside a
signal handler are: set a variable and exit. And in the first case, you
should only set a variable in such a way that malloc is not
called (eg, by setting a variable that already has a value).
For example:
$Interrupted = 0; # to ensure it has a value
$SIG{INT} = sub {
$Interrupted++;
syswrite(STDERR, "ouch\n", 5);
}
However, because syscalls restart by default, you'll find that if you're in a ``slow'' call, such as <FH>, read, connect, or wait, that the only way to terminate them is by ``longjumping'' out; that is, by raising an exception. See the time-out handler for a blocking flock in Signals or chapter 6 of the Camel.
pwd_mkdb to install it (see pwd_mkdb(5) for more details).
date 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";
gettimeofday, 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] );
atexit. Each package's END block is called when the program or
thread ends (see the perlmod manpage manpage for more details).
Perl's exception-handling mechanism is its eval operator. You can use eval as setjmp and die as longjmp. For details of this, see the section on signals, especially the time-out handler for a blocking flock in Signals and chapter 6 of the Camel.
If exception handling is all you're interested in, try the exceptions.pl library (part of the standard perl distribution).
If you want the atexit syntax (and an rmexit as
well), try the AtExit module available from CPAN.
Note that even though SunOS and Solaris are binary compatible, these values are different. Go figure.
Remember to check the modules that came with your distribution, and CPAN as well - someone may already have written a module to do it.
cpp
directives in C header files to files containing subroutine definitions,
like &SYS_getitimer, which you can use as arguments to your functions.
It doesn't work perfectly, but it usually gets most of the job done. Simple
files like errno.h, syscall.h, and socket.h were fine, but the hard ones like ioctl.h nearly always need to hand-edited. Here's how to install the *.ph files:
1. become super-user
2. cd /usr/include
3. h2ph *.h */*.h
If your system supports dynamic loading, for reasons of portability and sanity you probably ought to use h2xs (also part of the standard perl distribution). This tool converts C header files to Perl extensions. See the perlxstut manpage for how to get started with h2xs.
If your system doesn't support dynamic loading, you still probably ought to use h2xs. See the perlxstut manpage and MakeMaker for more information (in brief, just use make perl instead of a plain make to rebuild perl with a new static extension).
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! Details on why Perl's system and
backtick and pipe opens all use the Bourne shell are in
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 Open3).
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 execs 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.
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.
`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 $? to see whether the program even ran correctly. Even if you wrote
print `cat /etc/termcap`;
In most cases, this could and probably should be written as
system("cat /etc/termcap") == 0
or die "cat program failed!";
Which will get the output quickly (as its generated, instead of only at the end ) and also check the return value.
System also provides direct control over whether shell wildcard processing may take place, whereas backticks do not.
@ok = `grep @opts '$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, when you exec a list, so no shell escapes happen.
clearerr that you can use. That is the
technically correct way to do it. Here are some less reliable workarounds:
$where = tell(LOG);
seek(LOG, $where, 0);
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]";
evaling the script's output in your shell; check out the
comp.unix.questions FAQ for details.
fork && exit;
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.
-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";
}
sysopen:
use Fcntl;
sysopen(FH, "/tmp/somefile", O_WRONLY|O_NDELAY|O_CREAT, 0644)
or die "can't open /tmp/somefile: $!":
If your version of perl is compiled without dynamic loading, then you just need to replace step 3 (make) with make perl and you will get a new perl binary with your extension linked in.
See MakeMaker for more details on building extensions.