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#!/usr/bin/perl
use strict;
use warnings;
use feature 'say';
use autodie;
use FindBin '$RealBin';
use lib "$RealBin/lib";
use Vnlog::Util qw(parse_options read_and_preparse_input ensure_all_legends_equivalent close_nondev_inputs reconstruct_substituted_command);
# This comes from the struct option long_options in tail.c in GNU coreutils
my @specs = ( # options with no args
"silent|quiet|q",
"zero-terminated|z",
"verbose|v",
"retry",
"F",
"f",
# options with args
"bytes|c=s",
"lines|n=s",
"sleep-interval|s=f",
"max-unchanged-stats=i",
"pid=i",
# '--follow' and '--follow=...' are valid. '--follow ...' is NOT
# valid. parse_options handles that
"follow:s",
"vnl-tool=s",
"help");
my %options_unsupported = ( 'bytes' => <<'EOF',
vnlog is line-oriented, so I refuse to split lines
EOF
'zero-terminated' => <<'EOF'
vnlog is built on assuming a particular record separator
EOF
);
my ($filenames,$options) = parse_options(\@ARGV, \@specs, 0, <<EOF);
$0 [options] logfile logfile logfile ... < logfile
The most common options are (mostly from the GNU tail manpage)
-n, --lines=[+]NUM
output the last NUM lines, instead of the last 10;
or use -n +NUM to output starting with line NUM
-f, --follow[={name|descriptor}]
output appended data as the file grows;
an absent option argument means 'descriptor'
--vnl-tool tool
Specifies the path to the tool we're wrapping. By default we wrap 'tail',
so most people can omit this
EOF
$options->{'vnl-tool'} //= 'tail';
if( defined $options->{follow} &&
length($options->{follow}) > 0 &&
$options->{follow} ne 'name' &&
$options->{follow} ne 'descriptor' )
{
die "--follow can be given ONLY as --follow=name or --follow=descriptor";
}
for my $key(keys %$options)
{
if($options_unsupported{$key})
{
my $keyname = length($key) == 1 ? "-$key" : "--$key";
die("I don't support $keyname: $options_unsupported{$key}");
}
}
my $inputs = read_and_preparse_input($filenames,
# read all lines, including comments
['cat']);
ensure_all_legends_equivalent($inputs);
say '# ' . join(' ', @{$inputs->[0]{keys}});
# When looking at normal files, tail needs the original filenames to be able to
# do its thing. A pipe filter won't do; especially if we're doing a tail -f. But
# if the thing I'm tailing is a pipe to begin with, I need to give it that pipe.
# The NAME of the device won't do. Thus I call reconstruct_substituted_command()
# telling it to substitute the dev filenames, but leave non-dev filenames alone.
#
# Additionally, since I don't use the file filter anymore, I close those pipes
my $ARGV_new = reconstruct_substituted_command($inputs, $options, [], \@specs, 1);
close_nondev_inputs($inputs);
exec $options->{'vnl-tool'}, @$ARGV_new;
__END__
=head1 NAME
vnl-tail - tail a log file, preserving the legend
=head1 SYNOPSIS
$ read_temperature | tee temp.vnl
# temperature
29.5
30.4
28.3
22.1
... continually produces data
... at the same time, in another terminal
$ vnl-tail -f temp.vnl
# temperature
28.3
22.1
... outputs data as it comes in
=head1 DESCRIPTION
Usage: vnl-tail [options] logfile logfile logfile ... < logfile
This tool runs C<tail> on given vnlog files in various ways. C<vnl-tail> is a
wrapper around the GNU coreutils C<tail> tool. Since this is a wrapper, most
commandline options and behaviors of the C<tail> tool are present; consult the
L<tail(1)> manpage for detail. The differences from GNU coreutils C<tail> are
=over
=item *
The input and output to this tool are vnlog files, complete with a legend
=item *
C<-c> is not supported because vnlog really doesn't want to break up lines
=item *
C<--zero-terminated> is not supported because vnlog assumes
newline-separated records
=item *
By default we call the C<tail> tool to do the actual work. If the underlying
tool has a different name or lives in an odd path, this can be specified by
passing C<--vnl-tool TOOL>
=back
Past that, everything C<tail> does is supported, so see that man page for
detailed documentation.
=head1 COMPATIBILITY
I use GNU/Linux-based systems exclusively, but everything has been tested
functional on FreeBSD and OSX in addition to Debian, Ubuntu and CentOS. I can
imagine there's something I missed when testing on non-Linux systems, so please
let me know if you find any issues.
=head1 SEE ALSO
L<tail(1)>
=head1 REPOSITORY
https://github.com/dkogan/vnlog/
=head1 AUTHOR
Dima Kogan C<< <dima@secretsauce.net> >>
=head1 LICENSE AND COPYRIGHT
Copyright 2018 Dima Kogan C<< <dima@secretsauce.net> >>
This library is free software; you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License as published by the Free
Software Foundation; either version 2.1 of the License, or (at your option) any
later version.
=cut
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