=head1 NAME
-perlfaq5 - Files and Formats ($Revision: 1.37 $, $Date: 2005/08/10 15:55:23 $)
+perlfaq5 - Files and Formats ($Revision: 3606 $)
=head1 DESCRIPTION
Use select() to choose the desired handle, then set its
per-filehandle variables.
- $old_fh = select(OUTPUT_HANDLE);
- $| = 1;
- select($old_fh);
+ $old_fh = select(OUTPUT_HANDLE);
+ $| = 1;
+ select($old_fh);
Some idioms can handle this in a single statement:
- select((select(OUTPUT_HANDLE), $| = 1)[0]);
+ select((select(OUTPUT_HANDLE), $| = 1)[0]);
- $| = 1, select $_ for select OUTPUT_HANDLE;
+ $| = 1, select $_ for select OUTPUT_HANDLE;
Some modules offer object-oriented access to handles and their
variables, although they may be overkill if this is the only
thing you do with them. You can use IO::Handle:
- use IO::Handle;
- open(DEV, ">/dev/printer"); # but is this?
- DEV->autoflush(1);
+ use IO::Handle;
+ open(DEV, ">/dev/printer"); # but is this?
+ DEV->autoflush(1);
or IO::Socket:
- use IO::Socket; # this one is kinda a pipe?
- my $sock = IO::Socket::INET->new( 'www.example.com:80' ) ;
+ use IO::Socket; # this one is kinda a pipe?
+ my $sock = IO::Socket::INET->new( 'www.example.com:80' );
- $sock->autoflush();
+ $sock->autoflush();
=head2 How do I change one line in a file/delete a line in a file/insert a line in the middle of a file/append to the beginning of a file?
X<file, editing>
If your text file doesn't end with a newline, then it's not really a
proper text file, so this may report one fewer line than you expect.
- $lines = 0;
- open(FILE, $filename) or die "Can't open `$filename': $!";
- while (sysread FILE, $buffer, 4096) {
- $lines += ($buffer =~ tr/\n//);
- }
- close FILE;
+ $lines = 0;
+ open(FILE, $filename) or die "Can't open `$filename': $!";
+ while (sysread FILE, $buffer, 4096) {
+ $lines += ($buffer =~ tr/\n//);
+ }
+ close FILE;
This assumes no funny games with newline translations.
modifying the appropriate variables directly, you can get the same
behavior within a larger program. For example:
- # ...
- {
- local($^I, @ARGV) = ('.orig', glob("*.c"));
- while (<>) {
- if ($. == 1) {
- print "This line should appear at the top of each file\n";
- }
- s/\b(p)earl\b/${1}erl/i; # Correct typos, preserving case
- print;
- close ARGV if eof; # Reset $.
- }
- }
- # $^I and @ARGV return to their old values here
+ # ...
+ {
+ local($^I, @ARGV) = ('.orig', glob("*.c"));
+ while (<>) {
+ if ($. == 1) {
+ print "This line should appear at the top of each file\n";
+ }
+ s/\b(p)earl\b/${1}erl/i; # Correct typos, preserving case
+ print;
+ close ARGV if eof; # Reset $.
+ }
+ }
+ # $^I and @ARGV return to their old values here
This block modifies all the C<.c> files in the current directory,
leaving a backup of the original data from each file in a new
Otherwise, you can use the File::Temp module.
- use File::Temp qw/ tempfile tempdir /;
+ use File::Temp qw/ tempfile tempdir /;
- $dir = tempdir( CLEANUP => 1 );
- ($fh, $filename) = tempfile( DIR => $dir );
+ $dir = tempdir( CLEANUP => 1 );
+ ($fh, $filename) = tempfile( DIR => $dir );
- # or if you don't need to know the filename
+ # or if you don't need to know the filename
- $fh = tempfile( DIR => $dir );
+ $fh = tempfile( DIR => $dir );
The File::Temp has been a standard module since Perl 5.6.1. If you
don't have a modern enough Perl installed, use the C<new_tmpfile>
class method from the IO::File module to get a filehandle opened for
reading and writing. Use it if you don't need to know the file's name:
- use IO::File;
- $fh = IO::File->new_tmpfile()
+ use IO::File;
+ $fh = IO::File->new_tmpfile()
or die "Unable to make new temporary file: $!";
If you're committed to creating a temporary file by hand, use the
process ID and/or the current time-value. If you need to have many
temporary files in one process, use a counter:
- BEGIN {
+ BEGIN {
use Fcntl;
my $temp_dir = -d '/tmp' ? '/tmp' : $ENV{TMPDIR} || $ENV{TEMP};
my $base_name = sprintf("%s/%d-%d-0000", $temp_dir, $$, time());
+
sub temp_file {
- local *FH;
- my $count = 0;
- until (defined(fileno(FH)) || $count++ > 100) {
+ local *FH;
+ my $count = 0;
+ until (defined(fileno(FH)) || $count++ > 100) {
$base_name =~ s/-(\d+)$/"-" . (1 + $1)/e;
# O_EXCL is required for security reasons.
sysopen(FH, $base_name, O_WRONLY|O_EXCL|O_CREAT);
- }
- if (defined(fileno(FH))
+ }
+
+ if (defined(fileno(FH))
return (*FH, $base_name);
- } else {
+ }
+ else {
return ();
}
}
- }
+ }
=head2 How can I manipulate fixed-record-length files?
X<fixed-length> X<file, fixed-length records>
some fixed-format input lines, in this case from the output of a normal,
Berkeley-style ps:
- # sample input line:
- # 15158 p5 T 0:00 perl /home/tchrist/scripts/now-what
- my $PS_T = 'A6 A4 A7 A5 A*';
- open my $ps, '-|', 'ps';
- print scalar <$ps>;
- my @fields = qw( pid tt stat time command );
- while (<$ps>) {
- my %process;
- @process{@fields} = unpack($PS_T, $_);
+ # sample input line:
+ # 15158 p5 T 0:00 perl /home/tchrist/scripts/now-what
+ my $PS_T = 'A6 A4 A7 A5 A*';
+ open my $ps, '-|', 'ps';
+ print scalar <$ps>;
+ my @fields = qw( pid tt stat time command );
+ while (<$ps>) {
+ my %process;
+ @process{@fields} = unpack($PS_T, $_);
for my $field ( @fields ) {
- print "$field: <$process{$field}>\n";
+ print "$field: <$process{$field}>\n";
}
print 'line=', pack($PS_T, @process{@fields} ), "\n";
- }
+ }
We've used a hash slice in order to easily handle the fields of each row.
Storing the keys in an array means it's easy to operate on them as a
group or loop over them with for. It also avoids polluting the program
with global variables and using symbolic references.
-=head2 How can I make a filehandle local to a subroutine? How do I pass filehandles between subroutines? How do I make an array of filehandles?
+=head2 How can I make a filehandle local to a subroutine? How do I pass filehandles between subroutines? How do I make an array of filehandles?
X<filehandle, local> X<filehandle, passing> X<filehandle, reference>
As of perl5.6, open() autovivifies file and directory handles
process_file( $fh );
+If you like, you can store these filehandles in an array or a hash.
+If you access them directly, they aren't simple scalars and you
+need to give C<print> a little help by placing the filehandle
+reference in braces. Perl can only figure it out on its own when
+the filehandle reference is a simple scalar.
+
+ my @fhs = ( $fh1, $fh2, $fh3 );
+
+ for( $i = 0; $i <= $#fhs; $i++ ) {
+ print {$fhs[$i]} "just another Perl answer, \n";
+ }
+
+
Before perl5.6, you had to deal with various typeglob idioms
which you may see in older code.
in a place that a filehandle is expected. Here are ways
to get indirect filehandles:
- $fh = SOME_FH; # bareword is strict-subs hostile
- $fh = "SOME_FH"; # strict-refs hostile; same package only
- $fh = *SOME_FH; # typeglob
- $fh = \*SOME_FH; # ref to typeglob (bless-able)
- $fh = *SOME_FH{IO}; # blessed IO::Handle from *SOME_FH typeglob
+ $fh = SOME_FH; # bareword is strict-subs hostile
+ $fh = "SOME_FH"; # strict-refs hostile; same package only
+ $fh = *SOME_FH; # typeglob
+ $fh = \*SOME_FH; # ref to typeglob (bless-able)
+ $fh = *SOME_FH{IO}; # blessed IO::Handle from *SOME_FH typeglob
Or, you can use the C<new> method from one of the IO::* modules to
create an anonymous filehandle, store that in a scalar variable,
and use it as though it were a normal filehandle.
- use IO::Handle; # 5.004 or higher
- $fh = IO::Handle->new();
+ use IO::Handle; # 5.004 or higher
+ $fh = IO::Handle->new();
Then use any of those as you would a normal filehandle. Anywhere that
Perl is expecting a filehandle, an indirect filehandle may be used
the C<< <FH> >> diamond operator will accept either a named filehandle
or a scalar variable containing one:
- ($ifh, $ofh, $efh) = (*STDIN, *STDOUT, *STDERR);
- print $ofh "Type it: ";
- $got = <$ifh>
- print $efh "What was that: $got";
+ ($ifh, $ofh, $efh) = (*STDIN, *STDOUT, *STDERR);
+ print $ofh "Type it: ";
+ $got = <$ifh>
+ print $efh "What was that: $got";
If you're passing a filehandle to a function, you can write
the function in two ways:
- sub accept_fh {
- my $fh = shift;
- print $fh "Sending to indirect filehandle\n";
- }
+ sub accept_fh {
+ my $fh = shift;
+ print $fh "Sending to indirect filehandle\n";
+ }
Or it can localize a typeglob and use the filehandle directly:
- sub accept_fh {
- local *FH = shift;
- print FH "Sending to localized filehandle\n";
- }
+ sub accept_fh {
+ local *FH = shift;
+ print FH "Sending to localized filehandle\n";
+ }
Both styles work with either objects or typeglobs of real filehandles.
(They might also work with strings under some circumstances, but this
is risky.)
- accept_fh(*STDOUT);
- accept_fh($handle);
+ accept_fh(*STDOUT);
+ accept_fh($handle);
In the examples above, we assigned the filehandle to a scalar variable
before using it. That is because only simple scalar variables, not
something other than a simple scalar variable as a filehandle is
illegal and won't even compile:
- @fd = (*STDIN, *STDOUT, *STDERR);
- print $fd[1] "Type it: "; # WRONG
- $got = <$fd[0]> # WRONG
- print $fd[2] "What was that: $got"; # WRONG
+ @fd = (*STDIN, *STDOUT, *STDERR);
+ print $fd[1] "Type it: "; # WRONG
+ $got = <$fd[0]> # WRONG
+ print $fd[2] "What was that: $got"; # WRONG
With C<print> and C<printf>, you get around this by using a block and
an expression where you would place the filehandle:
- print { $fd[1] } "funny stuff\n";
- printf { $fd[1] } "Pity the poor %x.\n", 3_735_928_559;
- # Pity the poor deadbeef.
+ print { $fd[1] } "funny stuff\n";
+ printf { $fd[1] } "Pity the poor %x.\n", 3_735_928_559;
+ # Pity the poor deadbeef.
That block is a proper block like any other, so you can put more
complicated code there. This sends the message out to one of two places:
- $ok = -x "/bin/cat";
- print { $ok ? $fd[1] : $fd[2] } "cat stat $ok\n";
- print { $fd[ 1+ ($ok || 0) ] } "cat stat $ok\n";
+ $ok = -x "/bin/cat";
+ print { $ok ? $fd[1] : $fd[2] } "cat stat $ok\n";
+ print { $fd[ 1+ ($ok || 0) ] } "cat stat $ok\n";
This approach of treating C<print> and C<printf> like object methods
calls doesn't work for the diamond operator. That's because it's a
would work, but only because readline() requires a typeglob. It doesn't
work with objects or strings, which might be a bug we haven't fixed yet.
- $got = readline($fd[0]);
+ $got = readline($fd[0]);
Let it be noted that the flakiness of indirect filehandles is not
related to whether they're strings, typeglobs, objects, or anything else.
This subroutine will add commas to your number:
sub commify {
- local $_ = shift;
- 1 while s/^([-+]?\d+)(\d{3})/$1,$2/;
- return $_;
- }
+ local $_ = shift;
+ 1 while s/^([-+]?\d+)(\d{3})/$1,$2/;
+ return $_;
+ }
This regex from Benjamin Goldberg will add commas to numbers:
- s/(^[-+]?\d+?(?=(?>(?:\d{3})+)(?!\d))|\G\d{3}(?=\d))/$1,/g;
+ s/(^[-+]?\d+?(?=(?>(?:\d{3})+)(?!\d))|\G\d{3}(?=\d))/$1,/g;
It is easier to see with comments:
- s/(
- ^[-+]? # beginning of number.
- \d+? # first digits before first comma
- (?= # followed by, (but not included in the match) :
- (?>(?:\d{3})+) # some positive multiple of three digits.
- (?!\d) # an *exact* multiple, not x * 3 + 1 or whatever.
- )
- | # or:
- \G\d{3} # after the last group, get three digits
- (?=\d) # but they have to have more digits after them.
- )/$1,/xg;
+ s/(
+ ^[-+]? # beginning of number.
+ \d+? # first digits before first comma
+ (?= # followed by, (but not included in the match) :
+ (?>(?:\d{3})+) # some positive multiple of three digits.
+ (?!\d) # an *exact* multiple, not x * 3 + 1 or whatever.
+ )
+ | # or:
+ \G\d{3} # after the last group, get three digits
+ (?=\d) # but they have to have more digits after them.
+ )/$1,/xg;
=head2 How can I translate tildes (~) in a filename?
X<tilde> X<tilde expansion>
Because you're using something like this, which truncates the file and
I<then> gives you read-write access:
- open(FH, "+> /path/name"); # WRONG (almost always)
+ open(FH, "+> /path/name"); # WRONG (almost always)
Whoops. You should instead use this, which will fail if the file
doesn't exist.
- open(FH, "+< /path/name"); # open for update
+ open(FH, "+< /path/name"); # open for update
Using ">" always clobbers or creates. Using "<" never does
either. The "+" doesn't change this.
Here are examples of many kinds of file opens. Those using sysopen()
all assume
- use Fcntl;
+ use Fcntl;
To open file for reading:
- open(FH, "< $path") || die $!;
- sysopen(FH, $path, O_RDONLY) || die $!;
+ open(FH, "< $path") || die $!;
+ sysopen(FH, $path, O_RDONLY) || die $!;
To open file for writing, create new file if needed or else truncate old file:
- open(FH, "> $path") || die $!;
- sysopen(FH, $path, O_WRONLY|O_TRUNC|O_CREAT) || die $!;
- sysopen(FH, $path, O_WRONLY|O_TRUNC|O_CREAT, 0666) || die $!;
+ open(FH, "> $path") || die $!;
+ sysopen(FH, $path, O_WRONLY|O_TRUNC|O_CREAT) || die $!;
+ sysopen(FH, $path, O_WRONLY|O_TRUNC|O_CREAT, 0666) || die $!;
To open file for writing, create new file, file must not exist:
- sysopen(FH, $path, O_WRONLY|O_EXCL|O_CREAT) || die $!;
- sysopen(FH, $path, O_WRONLY|O_EXCL|O_CREAT, 0666) || die $!;
+ sysopen(FH, $path, O_WRONLY|O_EXCL|O_CREAT) || die $!;
+ sysopen(FH, $path, O_WRONLY|O_EXCL|O_CREAT, 0666) || die $!;
To open file for appending, create if necessary:
- open(FH, ">> $path") || die $!;
- sysopen(FH, $path, O_WRONLY|O_APPEND|O_CREAT) || die $!;
- sysopen(FH, $path, O_WRONLY|O_APPEND|O_CREAT, 0666) || die $!;
+ open(FH, ">> $path") || die $!;
+ sysopen(FH, $path, O_WRONLY|O_APPEND|O_CREAT) || die $!;
+ sysopen(FH, $path, O_WRONLY|O_APPEND|O_CREAT, 0666) || die $!;
To open file for appending, file must exist:
- sysopen(FH, $path, O_WRONLY|O_APPEND) || die $!;
+ sysopen(FH, $path, O_WRONLY|O_APPEND) || die $!;
To open file for update, file must exist:
- open(FH, "+< $path") || die $!;
- sysopen(FH, $path, O_RDWR) || die $!;
+ open(FH, "+< $path") || die $!;
+ sysopen(FH, $path, O_RDWR) || die $!;
To open file for update, create file if necessary:
- sysopen(FH, $path, O_RDWR|O_CREAT) || die $!;
- sysopen(FH, $path, O_RDWR|O_CREAT, 0666) || die $!;
+ sysopen(FH, $path, O_RDWR|O_CREAT) || die $!;
+ sysopen(FH, $path, O_RDWR|O_CREAT, 0666) || die $!;
To open file for update, file must not exist:
- sysopen(FH, $path, O_RDWR|O_EXCL|O_CREAT) || die $!;
- sysopen(FH, $path, O_RDWR|O_EXCL|O_CREAT, 0666) || die $!;
+ sysopen(FH, $path, O_RDWR|O_EXCL|O_CREAT) || die $!;
+ sysopen(FH, $path, O_RDWR|O_EXCL|O_CREAT, 0666) || die $!;
To open a file without blocking, creating if necessary:
- sysopen(FH, "/foo/somefile", O_WRONLY|O_NDELAY|O_CREAT)
+ sysopen(FH, "/foo/somefile", O_WRONLY|O_NDELAY|O_CREAT)
or die "can't open /foo/somefile: $!":
Be warned that neither creation nor deletion of files is guaranteed to
Unless you have a particular reason to use the two argument form you
should use the three argument form of open() which does not treat any
charcters in the filename as special.
-
+
open FILE, "<", " file "; # filename is " file "
open FILE, ">", ">file"; # filename is ">file"
If your operating system supports a proper mv(1) utility or its
functional equivalent, this works:
- rename($old, $new) or system("mv", $old, $new);
+ rename($old, $new) or system("mv", $old, $new);
It may be more portable to use the File::Copy module instead.
You just copy to the new file to the new name (checking return
A common bit of code B<NOT TO USE> is this:
- sleep(3) while -e "file.lock"; # PLEASE DO NOT USE
- open(LCK, "> file.lock"); # THIS BROKEN CODE
+ sleep(3) while -e "file.lock"; # PLEASE DO NOT USE
+ open(LCK, "> file.lock"); # THIS BROKEN CODE
This is a classic race condition: you take two steps to do something
which must be done in one. That's why computer hardware provides an
atomic test-and-set instruction. In theory, this "ought" to work:
- sysopen(FH, "file.lock", O_WRONLY|O_EXCL|O_CREAT)
+ sysopen(FH, "file.lock", O_WRONLY|O_EXCL|O_CREAT)
or die "can't open file.lock: $!";
except that lamentably, file creation (and deletion) is not atomic
Anyway, this is what you can do if you can't help yourself.
- use Fcntl qw(:DEFAULT :flock);
- sysopen(FH, "numfile", O_RDWR|O_CREAT) or die "can't open numfile: $!";
- flock(FH, LOCK_EX) or die "can't flock numfile: $!";
- $num = <FH> || 0;
- seek(FH, 0, 0) or die "can't rewind numfile: $!";
- truncate(FH, 0) or die "can't truncate numfile: $!";
- (print FH $num+1, "\n") or die "can't write numfile: $!";
- close FH or die "can't close numfile: $!";
+ use Fcntl qw(:DEFAULT :flock);
+ sysopen(FH, "numfile", O_RDWR|O_CREAT) or die "can't open numfile: $!";
+ flock(FH, LOCK_EX) or die "can't flock numfile: $!";
+ $num = <FH> || 0;
+ seek(FH, 0, 0) or die "can't rewind numfile: $!";
+ truncate(FH, 0) or die "can't truncate numfile: $!";
+ (print FH $num+1, "\n") or die "can't write numfile: $!";
+ close FH or die "can't close numfile: $!";
Here's a much better web-page hit counter:
- $hits = int( (time() - 850_000_000) / rand(1_000) );
+ $hits = int( (time() - 850_000_000) / rand(1_000) );
If the count doesn't impress your friends, then the code might. :-)
If you're just trying to patch a binary, in many cases something as
simple as this works:
- perl -i -pe 's{window manager}{window mangler}g' /usr/bin/emacs
+ perl -i -pe 's{window manager}{window mangler}g' /usr/bin/emacs
However, if you have fixed sized records, then you might do something more
like this:
- $RECSIZE = 220; # size of record, in bytes
- $recno = 37; # which record to update
- open(FH, "+<somewhere") || die "can't update somewhere: $!";
- seek(FH, $recno * $RECSIZE, 0);
- read(FH, $record, $RECSIZE) == $RECSIZE || die "can't read record $recno: $!";
- # munge the record
- seek(FH, -$RECSIZE, 1);
- print FH $record;
- close FH;
+ $RECSIZE = 220; # size of record, in bytes
+ $recno = 37; # which record to update
+ open(FH, "+<somewhere") || die "can't update somewhere: $!";
+ seek(FH, $recno * $RECSIZE, 0);
+ read(FH, $record, $RECSIZE) == $RECSIZE || die "can't read record $recno: $!";
+ # munge the record
+ seek(FH, -$RECSIZE, 1);
+ print FH $record;
+ close FH;
Locking and error checking are left as an exercise for the reader.
Don't forget them or you'll be quite sorry.
If you want to retrieve the time at which the file was last
read, written, or had its meta-data (owner, etc) changed,
-you use the B<-M>, B<-A>, or B<-C> file test operations as
+you use the B<-A>, B<-M>, or B<-C> file test operations as
documented in L<perlfunc>. These retrieve the age of the
file (measured against the start-time of your program) in
days as a floating point number. Some platforms may not have
Here's an example:
- $write_secs = (stat($file))[9];
- printf "file %s updated at %s\n", $file,
+ $write_secs = (stat($file))[9];
+ printf "file %s updated at %s\n", $file,
scalar localtime($write_secs);
If you prefer something more legible, use the File::stat module
(part of the standard distribution in version 5.004 and later):
- # error checking left as an exercise for reader.
- use File::stat;
- use Time::localtime;
- $date_string = ctime(stat($file)->mtime);
- print "file $file updated at $date_string\n";
+ # error checking left as an exercise for reader.
+ use File::stat;
+ use Time::localtime;
+ $date_string = ctime(stat($file)->mtime);
+ print "file $file updated at $date_string\n";
The POSIX::strftime() approach has the benefit of being,
in theory, independent of the current locale. See L<perllocale>
read and write times from its first argument to all the rest
of them.
- if (@ARGV < 2) {
- die "usage: cptimes timestamp_file other_files ...\n";
- }
- $timestamp = shift;
- ($atime, $mtime) = (stat($timestamp))[8,9];
- utime $atime, $mtime, @ARGV;
+ if (@ARGV < 2) {
+ die "usage: cptimes timestamp_file other_files ...\n";
+ }
+ $timestamp = shift;
+ ($atime, $mtime) = (stat($timestamp))[8,9];
+ utime $atime, $mtime, @ARGV;
Error checking is, as usual, left as an exercise for the reader.
If you only have to do this once, you can print individually
to each filehandle.
- for $fh (FH1, FH2, FH3) { print $fh "whatever\n" }
+ for $fh (FH1, FH2, FH3) { print $fh "whatever\n" }
=head2 How can I read in an entire file all at once?
X<slurp> X<file, slurping>
use File::Slurp;
$all_of_it = read_file($filename); # entire file in scalar
- @all_lines = read_file($filename); # one line perl element
+ @all_lines = read_file($filename); # one line perl element
The customary Perl approach for processing all the lines in a file is to
do so one line at a time:
- open (INPUT, $file) || die "can't open $file: $!";
- while (<INPUT>) {
- chomp;
- # do something with $_
- }
- close(INPUT) || die "can't close $file: $!";
+ open (INPUT, $file) || die "can't open $file: $!";
+ while (<INPUT>) {
+ chomp;
+ # do something with $_
+ }
+ close(INPUT) || die "can't close $file: $!";
This is tremendously more efficient than reading the entire file into
memory as an array of lines and then processing it one element at a time,
which is often--if not almost always--the wrong approach. Whenever
you see someone do this:
- @lines = <INPUT>;
+ @lines = <INPUT>;
you should think long and hard about why you need everything loaded at
once. It's just not a scalable solution. You might also find it more
You can read the entire filehandle contents into a scalar.
- {
+ {
local(*INPUT, $/);
open (INPUT, $file) || die "can't open $file: $!";
$var = <INPUT>;
- }
+ }
That temporarily undefs your record separator, and will automatically
close the file at block exit. If the file is already open, just use this:
- $var = do { local $/; <INPUT> };
+ $var = do { local $/; <INPUT> };
For ordinary files you can also use the read function.
interface (POSIX), you can use the following code, which you'll note
turns off echo processing as well.
- #!/usr/bin/perl -w
- use strict;
- $| = 1;
- for (1..4) {
- my $got;
- print "gimme: ";
- $got = getone();
- print "--> $got\n";
- }
+ #!/usr/bin/perl -w
+ use strict;
+ $| = 1;
+ for (1..4) {
+ my $got;
+ print "gimme: ";
+ $got = getone();
+ print "--> $got\n";
+ }
exit;
- BEGIN {
+ BEGIN {
use POSIX qw(:termios_h);
my ($term, $oterm, $echo, $noecho, $fd_stdin);
$noecho = $oterm & ~$echo;
sub cbreak {
- $term->setlflag($noecho);
- $term->setcc(VTIME, 1);
- $term->setattr($fd_stdin, TCSANOW);
- }
-
+ $term->setlflag($noecho);
+ $term->setcc(VTIME, 1);
+ $term->setattr($fd_stdin, TCSANOW);
+ }
+
sub cooked {
- $term->setlflag($oterm);
- $term->setcc(VTIME, 0);
- $term->setattr($fd_stdin, TCSANOW);
- }
+ $term->setlflag($oterm);
+ $term->setcc(VTIME, 0);
+ $term->setattr($fd_stdin, TCSANOW);
+ }
sub getone {
- my $key = '';
- cbreak();
- sysread(STDIN, $key, 1);
- cooked();
- return $key;
- }
+ my $key = '';
+ cbreak();
+ sysread(STDIN, $key, 1);
+ cooked();
+ return $key;
+ }
- }
+ }
- END { cooked() }
+ END { cooked() }
The Term::ReadKey module from CPAN may be easier to use. Recent versions
include also support for non-portable systems as well.
- use Term::ReadKey;
- open(TTY, "</dev/tty");
- print "Gimme a char: ";
- ReadMode "raw";
- $key = ReadKey 0, *TTY;
- ReadMode "normal";
- printf "\nYou said %s, char number %03d\n",
- $key, ord $key;
+ use Term::ReadKey;
+ open(TTY, "</dev/tty");
+ print "Gimme a char: ";
+ ReadMode "raw";
+ $key = ReadKey 0, *TTY;
+ ReadMode "normal";
+ printf "\nYou said %s, char number %03d\n",
+ $key, ord $key;
=head2 How can I tell whether there's a character waiting on a filehandle?
It's very system dependent. Here's one solution that works on BSD
systems:
- sub key_ready {
- my($rin, $nfd);
- vec($rin, fileno(STDIN), 1) = 1;
- return $nfd = select($rin,undef,undef,0);
- }
+ sub key_ready {
+ my($rin, $nfd);
+ vec($rin, fileno(STDIN), 1) = 1;
+ return $nfd = select($rin,undef,undef,0);
+ }
If you want to find out how many characters are waiting, there's
also the FIONREAD ioctl call to be looked at. The I<h2ph> tool that
can be C<require>d. FIONREAD ends up defined as a function in the
I<sys/ioctl.ph> file:
- require 'sys/ioctl.ph';
+ require 'sys/ioctl.ph';
- $size = pack("L", 0);
- ioctl(FH, FIONREAD(), $size) or die "Couldn't call ioctl: $!\n";
- $size = unpack("L", $size);
+ $size = pack("L", 0);
+ ioctl(FH, FIONREAD(), $size) or die "Couldn't call ioctl: $!\n";
+ $size = unpack("L", $size);
If I<h2ph> wasn't installed or doesn't work for you, you can
I<grep> the include files by hand:
- % grep FIONREAD /usr/include/*/*
- /usr/include/asm/ioctls.h:#define FIONREAD 0x541B
+ % grep FIONREAD /usr/include/*/*
+ /usr/include/asm/ioctls.h:#define FIONREAD 0x541B
Or write a small C program using the editor of champions:
- % cat > fionread.c
- #include <sys/ioctl.h>
- main() {
- printf("%#08x\n", FIONREAD);
- }
- ^D
- % cc -o fionread fionread.c
- % ./fionread
- 0x4004667f
+ % cat > fionread.c
+ #include <sys/ioctl.h>
+ main() {
+ printf("%#08x\n", FIONREAD);
+ }
+ ^D
+ % cc -o fionread fionread.c
+ % ./fionread
+ 0x4004667f
And then hard code it, leaving porting as an exercise to your successor.
- $FIONREAD = 0x4004667f; # XXX: opsys dependent
+ $FIONREAD = 0x4004667f; # XXX: opsys dependent
- $size = pack("L", 0);
- ioctl(FH, $FIONREAD, $size) or die "Couldn't call ioctl: $!\n";
- $size = unpack("L", $size);
+ $size = pack("L", 0);
+ ioctl(FH, $FIONREAD, $size) or die "Couldn't call ioctl: $!\n";
+ $size = unpack("L", $size);
FIONREAD requires a filehandle connected to a stream, meaning that sockets,
pipes, and tty devices work, but I<not> files.
First try
- seek(GWFILE, 0, 1);
+ seek(GWFILE, 0, 1);
The statement C<seek(GWFILE, 0, 1)> doesn't change the current position,
but it does clear the end-of-file condition on the handle, so that the
If you check L<perlfunc/open>, you'll see that several of the ways
to call open() should do the trick. For example:
- open(LOG, ">>/foo/logfile");
- open(STDERR, ">&LOG");
+ open(LOG, ">>/foo/logfile");
+ open(STDERR, ">&LOG");
Or even with a literal numeric descriptor:
numeric descriptor as with MHCONTEXT above. But if you really have
to, you may be able to do this:
- require 'sys/syscall.ph';
- $rc = syscall(&SYS_close, $fd + 0); # must force numeric
- die "can't sysclose $fd: $!" unless $rc == -1;
+ require 'sys/syscall.ph';
+ $rc = syscall(&SYS_close, $fd + 0); # must force numeric
+ die "can't sysclose $fd: $!" unless $rc == -1;
Or, just use the fdopen(3S) feature of open():
- {
+ {
local *F;
open F, "<&=$fd" or die "Cannot reopen fd=$fd: $!";
close F;
- }
+ }
=head2 Why can't I use "C:\temp\foo" in DOS paths? Why doesn't `C:\temp\foo.exe` work?
X<filename, DOS issues>
Here's an algorithm from the Camel Book:
- srand;
- rand($.) < 1 && ($line = $_) while <>;
+ srand;
+ rand($.) < 1 && ($line = $_) while <>;
This has a significant advantage in space over reading the whole file
in. You can find a proof of this method in I<The Art of Computer
Saying
- print "@lines\n";
+ print "@lines\n";
joins together the elements of C<@lines> with a space between them.
If C<@lines> were C<("little", "fluffy", "clouds")> then the above
statement would print
- little fluffy clouds
+ little fluffy clouds
but if each element of C<@lines> was a line of text, ending a newline
character C<("little\n", "fluffy\n", "clouds\n")> then it would print:
- little
- fluffy
- clouds
+ little
+ fluffy
+ clouds
If your array contains lines, just print them:
- print @lines;
+ print @lines;
+
+=head1 REVISION
+
+Revision: $Revision: 3606 $
+
+Date: $Date: 2006-03-06 12:05:47 +0100 (lun, 06 mar 2006) $
+
+See L<perlfaq> for source control details and availability.
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
+Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
other authors as noted. All rights reserved.
This documentation is free; you can redistribute it and/or modify it
projects / p5sagit/p5-mst-13.2.git / blobdiff