Boulder::Stream(3) User Contributed Perl Documentation Boulder::Stream(3)NAMEBoulder::Stream - Read and write tag/value data from an input stream
SYNOPSIS
#!/bin/perl
# Read a series of People records from STDIN.
# Add an "Eligible" tag to all those whose
# Age >= 35 and Friends list includes "Fred"
use Boulder::Stream;
# filestream way:
my $stream = Boulder::Stream->newFh;
while ( my $record = <$stream> ) {
next unless $record->Age >= 35;
my @friends = $record->Friends;
next unless grep {$_ eq 'Fred'} @friends;
$record->insert(Eligible => 'yes');
print $stream $record;
}
# object oriented way:
my $stream = Boulder::Stream->new;
while (my $record = $stream->get ) {
next unless $record->Age >= 35;
my @friends = $record->Friends;
next unless grep {$_ eq 'Fred'} @friends;
$record->insert(Eligible => 'yes');
print $stream $record;
}
DESCRIPTIONBoulder::Stream provides stream-oriented access to Boulder IO
hierarchical tag/value data. It can be used in a magic tied filehandle
mode, as shown in the synopsis, or in object-oriented mode. Using tied
filehandles, Stone objects are read from input using the standard <>
operator. Stone objects printed to the tied filehandle appear on the
output stream in Boulder format.
By default, data is read from the magic ARGV filehandle (STDIN or a
list of files provided on the command line) and written to STDOUT.
This can be changed to the filehandles of your choice.
Pass through behavior
When using the object-oriented form of Boulder::Stream, tags which
aren't specifically requested by the get() method are passed through to
output unchanged. This allows pipes of programs to be constructed
easily. Most programs will want to put the tags back into the boulder
stream once they're finished, potentially adding their own. Of course
some programs will want to behave differently. For example, a database
query program will generate but not read a boulderio stream, while a
report generator will read but not write the stream.
This convention allows the following type of pipe to be set up:
query_database | find_vector | find_dups | \
| blast_sequence | pick_primer | mail_report
If all the programs in the pipe follow the conventions, then it will be
possible to interpose other programs, such as a repetitive element
finder, in the middle of the pipe without disturbing other components.
SKELETON BOULDER PROGRAM
Here is a skeleton example.
#!/bin/perl
use Boulder::Stream;
my $stream = Boulder::Stream->newFh;
while ( my $record = <$stream> ) {
next unless $record->Age >= 35;
my @friends = $record->Friends;
next unless grep {$_ eq 'Fred'} @friends;
$record->insert(Eligible => 'yes');
print $stream $record;
}
The code starts by creating a Boulder::Stream object to handle the I/O.
It reads from the stream one record at a time, returning a Stone
object. We recover the Age and Friends tags, and continue looping
unless the Age is greater or equal to 35, and the list of Friends
contains "Fred". If these criteria match, then we insert a new tag
named Eligible and print the record to the stream. The output may look
like this:
Name=Janice
Age=36
Eligible=yes
Friends=Susan
Friends=Fred
Friends=Ralph
=
Name=Ralph
Age=42
Eligible=yes
Friends=Janice
Friends=Fred
=
Name=Susan
Age=35
Eligible=yes
Friends=Susan
Friends=Fred
=
Note that in this case only records that meet the criteria are echoed
to standard output. The object-oriented version of the program looks
like this:
#!/bin/perl
use Boulder::Stream;
my $stream = Boulder::Stream->new;
while ( my $record = $stream->get('Age','Friends') ) {
next unless $record->Age >= 35;
my @friends = $record->Friends;
next unless grep {$_ eq 'Fred'} @friends;
$record->insert(Eligible => 'yes');
$stream->put($record);
}
The get() method is used to fetch Stones containing one or more of the
indicated tags. The put() method is used to send the result to
standard output. The pass-through behavior might produce a set of
records like this one:
Name=Janice
Age=36
Eligible=yes
Friends=Susan
Friends=Fred
Friends=Ralph
=
Name=Phillip
Age=30
=
Name=Ralph
Age=42
Eligible=yes
Friends=Janice
Friends=Fred
=
Name=Barbara
Friends=Agatha
Friends=Janice
=
Name=Susan
Age=35
Eligible=yes
Friends=Susan
Friends=Fred
=
Notice that there are now two records ("Phillip" and "Barbara") that do
not contain the Eligible tag.
Boulder::Stream METHODS
$stream = Boulder::Stream->new(*IN,*OUT)
$stream = Boulder::Stream->new(-in=>*IN,-out=>*OUT)
The new() method creates a new Boulder::Stream object. You can provide
input and output filehandles. If you leave one or both undefined new()
will default to standard input or standard output. You are free to use
files, pipes, sockets, and other types of file handles. You may
provide the filehandle arguments as bare words, globs, or glob refs.
You are also free to use the named argument style shown in the second
heading.
$fh = Boulder::Stream->newFh(-in=>*IN, -out=>*OUT)
Returns a filehandle object tied to a Boulder::Stream object. Reads on
the filehandle perform a get(). Writes invoke a put().
To retrieve the underlying Boulder::Stream object, call Perl's built-in
tied() function:
$stream = tied $fh;
$stone = $stream->get(@taglist)
@stones = $stream->get(@taglist)
Every time get() is called, it will return a new Stone object. The
Stone will be created from the input stream, using just the tags
provided in the argument list. Pass no tags to receive whatever tags
are present in the input stream.
If none of the tags that you specify are in the current boulder record,
you will receive an empty Stone. At the end of the input stream, you
will receive undef.
If called in an array context, get() returns a list of all stones from
the input stream that contain one or more of the specified tags.
$stone = $stream->read_record(@taglist)
Identical to get(>, but the name is longer.
$stream->put($stone)
Write a Stone to the output filehandle.
$stream->write_record($stone)
Identical to put(), but the name is longer.
Useful State Variables in a Boulder::Stream
Every Boulder::Stream has several state variables that you can adjust.
Fix them in this fashion:
$a = new Boulder::Stream;
$a->{delim}=':';
$a->{record_start}='[';
$a->{record_end}=']';
$a->{passthru}=undef;
· delim
This is the delimiter character between tags and values, "=" by
default.
· record_start
This is the start of nested record character, "{" by default.
· record_end
This is the end of nested record character, "}" by default.
· passthru
This determines whether unrecognized tags should be passed through
from the input stream to the output stream. This is 'true' by
default. Set it to undef to override this behavior.
BUGS
Because the delim, record_start and record_end characters in the
Boulder::Stream object are used in optimized (once-compiled) pattern
matching, you cannot change these values once get() has once been
called. To change the defaults, you must create the Boulder::Stream,
set the characters, and only then begin reading from the input stream.
For the same reason, different Boulder::Stream objects cannot use
different delimiters.
AUTHOR
Lincoln D. Stein <lstein@cshl.org>, Cold Spring Harbor Laboratory, Cold
Spring Harbor, NY. This module can be used and distributed on the same
terms as Perl itself.
SEE ALSO
Boulder, Boulder::Blast, Boulder::Genbank, Boulder::Medline,
Boulder::Unigene, Boulder::Omim, Boulder::SwissProt
perl v5.14.1 2001-06-11 Boulder::Stream(3)
