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7.7. Caching Open Output Filehandles
7.7.1. Problem
You need more output files open
simultaneously than your system allows.
7.7.2. Solution
Use the
standard FileCache
module:
use FileCache;
cacheout ($path); # each time you use a filehandle
print $path "output";
7.7.3. Discussion
FileCache's
cacheout function lets you work with more output
files than your operating system lets you have open at any one time.
If you use it to open an existing file that FileCache is seeing for
the first time, the file is truncated to length zero, no questions
asked. However, in its opening and closing of files in the
background, cacheout tracks files it has opened
before and does not overwrite them, but appends to them instead. This
does not create directories for you, so if you give it
/usr/local/dates/merino.ewe to open but the
directory /usr/local/dates doesn't exist,
cacheout will die.The cacheout
function checks the value of the C-level constant
NOFILE from the standard system include file
sys/param.h to determine how many concurrently
open files are allowed on your system. This value can be incorrect on
some systems and even missing on a few (for instance, on those where
the maximum number of open file descriptors is a process resource
limit that can be set with the limit or
ulimit commands). If cacheout
can't get a value for NOFILE, set
$FileCache::cacheout_maxopen to be four less than
the correct value, or choose a reasonable number by trial and error.Example 7-1 splits an xferlog
file (created by most FTP servers nowadays) into separate files, each
named after the authenticated user. Fields in
xferlog files are space-separated, with the
fourth field from the last holding the authenticated username.
Example 7-1. splitwulog
#!/usr/bin/perl
# splitwulog - split wuftpd log by authenticated user
use FileCache;
$outdir = "/var/log/ftp/by-user";
while (<>) {
unless (defined ($user = (split)[-4])) {
warn "Invalid line: $.\n";
next;
}
$path = "$outdir/$user";
cacheout $path;
print $path $_;
}
7.7.4. See Also
Documentation for the standard FileCache module (also in Chapter 32
of Programming Perl); the
open function in perlfunc(1)
and in Chapter 29 of Programming Perl
