没有tail,仅Perl 的解决方案并不是那么不合理。
一种方法是从文件末尾查找,然后从中读取行。如果您没有足够的线条,请从末尾进一步寻找并重试。
sub last_x_lines {
my ($filename, $lineswanted) = @_;
my ($line, $filesize, $seekpos, $numread, @lines);
open F, $filename or die "Can't read $filename: $!\n";
$filesize = -s $filename;
$seekpos = 50 * $lineswanted;
$numread = 0;
while ($numread < $lineswanted) {
@lines = ();
$numread = 0;
seek(F, $filesize - $seekpos, 0);
<F> if $seekpos < $filesize; # Discard probably fragmentary line
while (defined($line = <F>)) {
push @lines, $line;
shift @lines if ++$numread > $lineswanted;
}
if ($numread < $lineswanted) {
# We didn't get enough lines. Double the amount of space to read from next time.
if ($seekpos >= $filesize) {
die "There aren't even $lineswanted lines in $filename - I got $numread\n";
}
$seekpos *= 2;
$seekpos = $filesize if $seekpos >= $filesize;
}
}
close F;
return @lines;
}
PS 一个更好的标题应该是“从 Perl 中的大文件末尾读取行”。