Programming Perl, 4th Edition

binmode

binmode FILEHANDLE, IOLAYER
binmode FILEHANDLE

This function arranges for the FILEHANDLE to have the semantics specified by the IOLAYER argument. If IOLAYER is omitted, binary (or “raw”) semantics are applied to the filehandle. If FILEHANDLE is an expression, the value is taken as the name of the filehandle or a reference to a filehandle, as appropriate. The function returns true if it succeeded, false otherwise.

The binmode function should be called after the open but before any I/O is done on the filehandle. The only way to reset the mode on a filehandle is to reopen the file, since the various layers may have treasured up various bits and pieces of data in various buffers. This restriction may be relaxed in the future.

In olden days, binmode was used primarily on operating systems whose runtime libraries distinguished text from binary files. On those systems, the purpose of binmode was to turn off the default text semantics. However, with the advent of Unicode and its many different storage encodings, programs on all systems must take some cognizance of the distinction.

These days there is only one kind of binary file (as far as Perl is concerned), but there are many kinds of text files, which Perl would also like to treat in a single way. So Perl has a single internal format for Unicode text, UTF-8.

Since there are many kinds of text files, text files often need to be translated ...