How do I copy out the last line written in a file?

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question: ⭐ (files)

Replies are listed 'Best First'.
Re: How do I copy out the last line written in a file?⭐ by Fastolfe (Vicar) on Sep 19, 2000 at 01:53 UTC
There are three commonly proposed methods to do this: Read the entire file `@array = <FILE>; $last_line = $array[$#array];` [download] This involves reading the entire file before examining the last line, which can be costly in memory and performance for large files. Seek to the end and backtrack `seek(FILE, -81, 2); # 81 bytes from the end, which should +be enough @lines = <FILE>; $last_line = $lines[$#lines]; # similar to above, but we don't read +much` [download] Use File::ReadBackwards `tie *FILE, File::ReadBackwards 'input_file'; while (<FILE>) { # line-by-line starting from the end }` [download] This latter method is supposed to be efficient and fast, so I imagine it uses some variation of the seek() method above.	[reply] [d/l] [select]
Re: Answer: How do I copy out the last line written in a file? by Anonymous Monk on May 03, 2007 at 01:56 UTC
When a file is read into an array the last element in the array array-1 would give you what you are looking for. Shashidhar Iddamsetty	[reply]
Re^2: Answer: How do I copy out the last line written in a file? by blazar (Canon) on May 03, 2007 at 10:18 UTC
When a file is read into an array the last element in the array array-1 would give you what you are looking for. To put it more clearly, and in actual Perl rather than some pseudo-language, the first example above, i.e. `@array = <FILE>; $last_line = $array[$#array];` [download] could be rewritten like `@array = <FILE>; $last_line = $array[-1];` [download] or even without creating an intermediate `@array`: `my $last_line = (<FILE>)[-1];` [download] Incidentally, I put a my in front of that as a reminder of the good rule of always staying strict.	[reply] [d/l] [select]
Re: How do I copy out the last line written in a file?⭐ by merlyn (Sage) on Sep 19, 2000 at 02:07 UTC
And don't forget File::Tail, which can keep up with the file as it grows (of which this request is often a part).	[reply]
Re: How do I copy out the last line written in a file? by I0 (Priest) on Nov 17, 2004 at 00:38 UTC
use Tie::File: `use Tie::File; sub last_line_of_file { my $file = shift; tie my @array, 'Tie::File', $file or die "read $file - $!"; $array[-1] }` [download]	[reply] [d/l]