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man : IO::Scalar
IO::Scalar(3p) User Contributed Perl Documentation IO::Scalar(3p)
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";
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### 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
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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.
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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?
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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
David F. Skoll (dfsATroaringpenguin.com).
Principal author
Eryq (eryqATzeegee.com). President, ZeeGee Software Inc
(http://www.zeegee.com).
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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.
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