How can I get the high-res mtime for a symbolic link in Perl?

Question

I want to reproduce the output of ls --full-time from a Perl script to avoid the overhead of calling ls several thousand times. I was hoping to use the stat function and grab all the information from there. However, the timestamp in the ls output uses the high-resolution clock so it includes the number of nanoseconds as well (according to the GNU docs, this is because --full-time is equivalent to --format=long --time-style=full-iso, and the full-iso time style includes the nanoseconds).

I came across the Time::HiRes module, which overrides the standard stat function with one that returns atime/mtime/ctime as floating point numbers, but there's no override for lstat. This is a problem, because calling stat on a symlink returns info for the linked file, not for the link itself.

So my question is this - where can I find a version of lstat that returns atime/mtime/ctime in the same way as Time::HiRes::stat? Failing that, is there another way to get the modtime for a symlink in high resolution (other than calling ls).

Answer 1

Your best bet would be to ask for lstat to be added to Time::HiRes. In fact, you could probably do it yourself. I'd bet that all you need to do is copy the function that starts

void
stat(...)

in HiRes.xs, change stat(...) to lstat(...) & OP_STAT to OP_LSTAT, add lstat to @EXPORT_OK in HiRes.pm, and recompile. Then submit a patch so others can benefit.

Answer 2

If you are willing to use Inline::C, this will work with recent linux

#!/usr/bin/perl

use strict;
use warnings;

use Inline C => <<'EOC';

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

long mtime_nsec(char* fname)
{
    struct stat st;
    if (-1 == lstat(fname, &st))
        return -1;
    return (long)st.st_mtim.tv_nsec;
}
EOC

print mtime_nsec($ARGV[0]);