Programming Perl, 4th Edition

read

read FILEHANDLE, SCALAR, LENGTH, OFFSET
read FILEHANDLE, SCALAR, LENGTH

This function tries to read LENGTH characters (meaning codepoints, not graphemes) of data into variable SCALAR from the specified FILEHANDLE. The function returns the number of characters read or 0 at end-of-file. It returns undef on error. SCALAR will grow or shrink to the length actually read. The OFFSET, if specified, determines where in the variable to start putting characters so that you can read into the middle of a string.

To copy data from filehandle FROM into filehandle TO, you could say:

while (read(FROM, $buf, 16384)) {
    print TO $buf;
}

Note the characters: depending on the status of the filehandle, either (8-bit) bytes or characters are read. A byte is just Perl’s way of talking about undecoded codepoints with small values. By default, all filehandles operate on bytes. But, for example, if the filehandle has been opened with the :utf8 I/O layer, the I/O will operate on UTF-8-encoded Unicode characters, not bytes. Similarly for the two-argument form of binmode, the middle argument to open, or via the ...