IO::Scalar(3pm) User Contributed Perl Documentation IO::Scalar(3pm)
NAME
IO::Scalar - IO:: interface for reading/writing a scalar
SYNOPSIS
Perform I/O on strings, using the basic OO interface...
use 5.005;
use IO::Scalar;
$data = "My message:\n";
### Open a handle on a string, and append to it:
$SH = new IO::Scalar \$data;
$SH->print("Hello");
$SH->print(", world!\nBye now!\n");
print "The string is now: ", $data, "\n";
### Open a handle on a string, read it line-by-line, then close it:
$SH = new IO::Scalar \$data;
while (defined($_ = $SH->getline)) {
print "Got line: $_";
}
$SH->close;
### Open a handle on a string, and slurp in all the lines:
$SH = new IO::Scalar \$data;
print "All lines:\n", $SH->getlines;
### Get the current position (either of two ways):
$pos = $SH->getpos;
$offset = $SH->tell;
### Set the current position (either of two ways):
$SH->setpos($pos);
$SH->seek($offset, 0);
### Open an anonymous temporary scalar:
$SH = new IO::Scalar;
$SH->print("Hi there!");
print "I printed: ", ${$SH->sref}, "\n"; ### get at value
Don't like OO for your I/O? No problem. Thanks to the magic of an
invisible tie(), the following now works out of the box, just as it
does with IO::Handle:
use 5.005;
use IO::Scalar;
$data = "My message:\n";
### Open a handle on a string, and append to it:
$SH = new IO::Scalar \$data;
print $SH "Hello";
print $SH ", world!\nBye now!\n";
print "The string is now: ", $data, "\n";
### Open a handle on a string, read it line-by-line, then close it:
$SH = new IO::Scalar \$data;
while (<$SH>) {
print "Got line: $_";
}
close $SH;
### Open a handle on a string, and slurp in all the lines:
$SH = new IO::Scalar \$data;
print "All lines:\n", <$SH>;
### Get the current position (WARNING: requires 5.6):
$offset = tell $SH;
### Set the current position (WARNING: requires 5.6):
seek $SH, $offset, 0;
### Open an anonymous temporary scalar:
$SH = new IO::Scalar;
print $SH "Hi there!";
print "I printed: ", ${$SH->sref}, "\n"; ### get at value
And for you folks with 1.x code out there: the old tie() style still
works, though this is unnecessary and deprecated:
use IO::Scalar;
### Writing to a scalar...
my $s;
tie *OUT, 'IO::Scalar', \$s;
print OUT "line 1\nline 2\n", "line 3\n";
print "String is now: $s\n"
### Reading and writing an anonymous scalar...
tie *OUT, 'IO::Scalar';
print OUT "line 1\nline 2\n", "line 3\n";
tied(OUT)->seek(0,0);
while (<OUT>) {
print "Got line: ", $_;
}
Stringification works, too!
my $SH = new IO::Scalar \$data;
print $SH "Hello, ";
print $SH "world!";
print "I printed: $SH\n";
DESCRIPTION
This class is part of the IO::Stringy distribution; see IO::Stringy for
change log and general information.
The IO::Scalar class implements objects which behave just like
IO::Handle (or FileHandle) objects, except that you may use them to
write to (or read from) scalars. These handles are automatically
tiehandle'd (though please see "WARNINGS" for information relevant to
your Perl version).
Basically, this:
my $s;
$SH = new IO::Scalar \$s;
$SH->print("Hel", "lo, "); ### OO style
$SH->print("world!\n"); ### ditto
Or this:
my $s;
$SH = tie *OUT, 'IO::Scalar', \$s;
print OUT "Hel", "lo, "; ### non-OO style
print OUT "world!\n"; ### ditto
Causes $s to be set to:
"Hello, world!\n"
PUBLIC INTERFACE
Construction
new [ARGS...]
Class method. Return a new, unattached scalar handle. If any
arguments are given, they're sent to open().
open [SCALARREF]
Instance method. Open the scalar handle on a new scalar, pointed
to by SCALARREF. If no SCALARREF is given, a "private" scalar is
created to hold the file data.
Returns the self object on success, undefined on error.
opened
Instance method. Is the scalar handle opened on something?
close
Instance method. Disassociate the scalar handle from its
underlying scalar. Done automatically on destroy.
Input and output
flush
Instance method. No-op, provided for OO compatibility.
fileno
Instance method. No-op, returns undef
getc
Instance method. Return the next character, or undef if none
remain.
getline
Instance method. Return the next line, or undef on end of string.
Can safely be called in an array context. Currently, lines are
delimited by "\n".
getlines
Instance method. Get all remaining lines. It will croak() if
accidentally called in a scalar context.
print ARGS...
Instance method. Print ARGS to the underlying scalar.
Warning: this continues to always cause a seek to the end of the
string, but if you perform seek()s and tell()s, it is still safer
to explicitly seek-to-end before subsequent print()s.
read BUF, NBYTES, [OFFSET]
Instance method. Read some bytes from the scalar. Returns the
number of bytes actually read, 0 on end-of-file, undef on error.
write BUF, NBYTES, [OFFSET]
Instance method. Write some bytes to the scalar.
sysread BUF, LEN, [OFFSET]
Instance method. Read some bytes from the scalar. Returns the
number of bytes actually read, 0 on end-of-file, undef on error.
syswrite BUF, NBYTES, [OFFSET]
Instance method. Write some bytes to the scalar.
Seeking/telling and other attributes
autoflush
Instance method. No-op, provided for OO compatibility.
binmode
Instance method. No-op, provided for OO compatibility.
clearerr
Instance method. Clear the error and EOF flags. A no-op.
eof Instance method. Are we at end of file?
seek OFFSET, WHENCE
Instance method. Seek to a given position in the stream.
sysseek OFFSET, WHENCE
Instance method. Identical to "seek OFFSET, WHENCE", q.v.
tell
Instance method. Return the current position in the stream, as a
numeric offset.
setpos POS
Instance method. Set the current position, using the opaque value
returned by "getpos()".
getpos
Instance method. Return the current position in the string, as an
opaque object.
sref
Instance method. Return a reference to the underlying scalar.
WARNINGS
Perl's TIEHANDLE spec was incomplete prior to 5.005_57; it was missing
support for "seek()", "tell()", and "eof()". Attempting to use these
functions with an IO::Scalar will not work prior to 5.005_57.
IO::Scalar will not have the relevant methods invoked; and even worse,
this kind of bug can lie dormant for a while. If you turn warnings on
(via $^W or "perl -w"), and you see something like this...
attempt to seek on unopened filehandle
...then you are probably trying to use one of these functions on an
IO::Scalar with an old Perl. The remedy is to simply use the OO
version; e.g.:
$SH->seek(0,0); ### GOOD: will work on any 5.005
seek($SH,0,0); ### WARNING: will only work on 5.005_57 and beyond
VERSION
$Id: Scalar.pm,v 1.6 2005/02/10 21:21:53 dfs Exp $
AUTHORS
Primary Maintainer
Dianne Skoll (dfs@roaringpenguin.com).
Principal author
Eryq (eryq@zeegee.com). President, ZeeGee Software Inc
(http://www.zeegee.com).
Other contributors
The full set of contributors always includes the folks mentioned in
"CHANGE LOG" in IO::Stringy. But just the same, special thanks to the
following individuals for their invaluable contributions (if I've
forgotten or misspelled your name, please email me!):
Andy Glew, for contributing "getc()".
Brandon Browning, for suggesting "opened()".
David Richter, for finding and fixing the bug in "PRINTF()".
Eric L. Brine, for his offset-using read() and write() implementations.
Richard Jones, for his patches to massively improve the performance of
"getline()" and add "sysread" and "syswrite".
B. K. Oxley (binkley), for stringification and inheritance
improvements, and sundry good ideas.
Doug Wilson, for the IO::Handle inheritance and automatic tie-ing.
SEE ALSO
IO::String, which is quite similar but which was designed more-recently
and with an IO::Handle-like interface in mind, so you could mix OO- and
native-filehandle usage without using tied().
Note: as of version 2.x, these classes all work like their IO::Handle
counterparts, so we have comparable functionality to IO::String.
perl v5.28.1 2019-02-28 IO::Scalar(3pm)
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