PerlIO::scalar(3perl) Perl Programmers Reference Guide PerlIO::scalar(3perl)

PerlIO::scalar - in-memory IO, scalar IO

my $scalar = '';
...
open my $fh, "<",  \$scalar or die;
open my $fh, ">",  \$scalar or die;
open my $fh, ">>", \$scalar or die;

or

my $scalar = '';
...
open my $fh, "<:scalar",  \$scalar or die;
open my $fh, ">:scalar",  \$scalar or die;
open my $fh, ">>:scalar", \$scalar or die;

A filehandle is opened but the file operations are performed "in-memory" on a scalar variable. All the normal file operations can be performed on the handle. The scalar is considered a stream of bytes. Currently fileno($fh) returns -1.

Attempting to open a read-only scalar for writing will fail, and if warnings are enabled, produce a warning.

"PerlIO::scalar" only exists to use XSLoader to load C code that provides support for treating a scalar as an "in memory" file. One does not need to explicitly "use PerlIO::scalar".
2021-05-23 perl v5.34.0