#!/usr/bin/perl -w

#
# dbcol.pm
# Copyright (C) 1991-2022 by John Heidemann <johnh@isi.edu>
#
# This program is distributed under terms of the GNU general
# public license, version 2.  See the file COPYING
# in $dblibdir for details.
#


=head1 NAME

dbcol - select columns from an Fsdb file

=head1 SYNOPSIS

dbcol [-v] [-e -] [column...]

=head1 DESCRIPTION

Select one or more columns from the input database.
If a value is given for empty columns with the -e option,
then any named columns which don't exist will be created.
Otherwise, non-existent columns are an error.

Note:  a safer way to create columns is dbcolcreate.

=head1 OPTIONS

=over 4

=item B<-r> or B<--relaxed-errors>

Relaxed error checking: ignore columns that aren't there.

=item B<-v> or B<--invert-match>

Output all columns except those listed (like grep -v).

=item B<-a> or B<--all>

Output all columns, in addition to those listed.
(Thus C<-a foo> will move column foo to the first column.)

=item B<-e> EmptyValue or B<--empty>

Specify the value newly created columns get.

=item B<--saveoutput $OUT_REF>

Save output writer (for integration with other fsdb filters).

=back

=for comment
begin_standard_fsdb_options

and the standard fsdb options:

=over 4

=item B<-d>

Enable debugging output.

=item B<-i> or B<--input> InputSource

Read from InputSource, typically a file, or - for standard input,
or (if in Perl) a IO::Handle, Fsdb::IO or Fsdb::BoundedQueue objects.

=item B<-o> or B<--output> OutputDestination

Write to OutputDestination, typically a file, or - for standard output,
or (if in Perl) a IO::Handle, Fsdb::IO or Fsdb::BoundedQueue objects.

=item B<--autorun> or B<--noautorun>

By default, programs process automatically,
but Fsdb::Filter objects in Perl do not run until you invoke
the run() method.
The C<--(no)autorun> option controls that behavior within Perl.

=item B<--header> H

Use H as the full Fsdb header, rather than reading a header from
then input.

=item B<--help>

Show help.

=item B<--man>

Show full manual.

=back

=for comment
end_standard_fsdb_options


=head1 SAMPLE USAGE

=head2 Input:

    #fsdb account passwd uid gid fullname homedir shell
    johnh * 2274 134 John_Heidemann /home/johnh /bin/bash
    greg * 2275 134 Greg_Johnson /home/greg /bin/bash
    root * 0 0 Root /root /bin/bash
    # this is a simple database

=head2 Command:

    cat DATA/passwd.fsdb account | dbcol account

=head2 Output:

    #fsdb      account
    johnh
    greg
    root
    # this is a simple database
    #  | dbcol account


=head1 SEE ALSO

L<dbcolcreate(1)>,
L<Fsdb(3)>

=cut


# WARNING: This code is derived from dbcol.pm; that is the master copy.

use Fsdb::Filter::dbcol;
my $f = new Fsdb::Filter::dbcol(@ARGV);
$f->setup_run_finish;  # or could just --autorun
exit 0;


=head1 AUTHOR and COPYRIGHT

Copyright (C) 1991-2022 by John Heidemann <johnh@isi.edu>

This program is distributed under terms of the GNU general
public license, version 2.  See the file COPYING
with the distribution for details.

=cut

1;