February 2012
Intermediate to advanced
1184 pages
37h 17m
English
Content preview from Programming Perl, 4th Editionsysread
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sysread 
sysreadFILEHANDLE,SCALAR,LENGTH,OFFSETsysreadFILEHANDLE,SCALAR,LENGTH
This function tries to read LENGTH characters
of data into variable SCALAR from the
specified FILEHANDLE using a low-level
syscall, read(2). The function returns the number
of characters read, or 0 at EOF.[251] The sysread function
returns undef on error.
SCALAR will grow or shrink to the length
actually read. The OFFSET, if specified, says
where in the string to start putting the characters so that you can read
into the middle of a string that’s being used as a buffer. For an
example of using OFFSET, see syswrite. An exception is raised if
LENGTH is negative or if
OFFSET points outside the string.
If the filehandle has no encoding layer, then the characters read in are no larger than 255, so they are effectively bytes.
Be prepared to handle the problems (like interrupted syscalls)
that standard I/O normally handles
for you. Because it bypasses standard I/O, do not mix sysread with other kinds of reads, ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.