See the current Perl documentation for write.
Here is our local, out-dated (pre-5.6) version:
write - print a picture record
Writes a formatted record (possibly multi-line) to the specified
FILEHANDLE, using the format associated with that
file. By default the format for a file is the one having the same name as
the filehandle, but the format for the current output channel (see the select() function) may be set explicitly by assigning the name of the format to the
Top of form processing is handled automatically: if there is insufficient room on the current page for the formatted record, the page is advanced by writing a form feed, a special top-of-page format is used to format the new page header, and then the record is written. By default the top-of-page format is the name of the filehandle with
``_TOP'' appended, but it may be dynamically set to the format of your choice by assigning the name to the
$^ variable while the filehandle is selected. The number of lines remaining on
the current page is in variable
$-, which can be set to
0 to force a new page.
If FILEHANDLE is unspecified, output goes to the current default output channel, which starts out as STDOUT but may be changed by the select() operator. If the FILEHANDLE is an EXPR, then the expression is evaluated and the resulting string is used to look up the name of the FILEHANDLE at run time. For more on formats, see the perlform manpage.
Note that write is NOT the opposite of read(). Unfortunately.