=pod

=encoding UTF-8

=head1 NAME

File::ByLine - Line-by-line file access loops

=head1 VERSION

version 1.181861

=head1 SYNOPSIS

  use File::ByLine;

  #
  # Procedural Interface (Simple!)
  #

  # Execute a routine for each line of a file
  dolines { say "Line: $_" } "file.txt";
  forlines "file.txt", sub { say "Line: $_" };

  # Grep (match) lines of a file
  my (@result) = greplines { m/foo/ } "file.txt";

  # Apply a function to each line and return result
  my (@result) = maplines { lc($_) } "file.txt";

  # Parallelized forlines/dolines routines
  # (Note: Requires Parallel::WorkUnit to be installed)
  parallel_dolines { foo($_) } "file.txt", 10;
  parallel_forlines "file.txt", 10, sub { foo($_); };

  # Parallelized maplines and greplines
  my (@result) = parallel_greplines { m/foo/ } "file.txt", 10;
  my (@result) = parallel_maplines  { lc($_) } "file.txt", 10;

  # Read an entire file, split into lines
  my (@result) = readlines "file.txt";


  #
  # Functional Interface
  #

  # Execute a routine for each line of a file
  my $byline = File::ByLine->new();
  $byline->do( sub { say "Line: $_" }, "file.txt");

  # Grep (match) lines of a file
  my $byline = File::ByLine->new();
  my (@result) = $byline->grep( sub { m/foo/ }, "file.txt");

  # Apply a function to each line and return result
  my $byline = File::ByLine->new();
  my (@result) = $byline->map( sub { lc($_) }, "file.txt");

  # Parallelized routines
  # (Note: Requires Parallel::WorkUnit to be installed)
  my $byline = File::ByLine->new();
  $byline->processes(10);
  $byline->do( sub { foo($_) }, "file.txt");
  my (@grep_result) = $byline->grep( sub { m/foo/ }, "file.txt");
  my (@map_result)  = $byline->map( sub { lc($_) }, "file.txt");

  # Skip the header line
  my $byline = File::ByLine->new();
  $byline->skip_header(1);
  $byline->do( sub { foo($_) }, "file.txt");
  my (@grep_result) = $byline->grep( sub { m/foo/ }, "file.txt");
  my (@map_result)  = $byline->map( sub { lc($_) }, "file.txt");

  # Process the header line
  my $byline = File::ByLine->new();
  $byline->header_handler( sub { say $_; } );
  $byline->do( sub { foo($_) }, "file.txt");
  my (@grep_result) = $byline->grep( sub { m/foo/ }, "file.txt");
  my (@map_result)  = $byline->map( sub { lc($_) }, "file.txt");

  # Read an entire file, split into lines
  my (@result) = readlines "file.txt";

  # Alternative way of specifying filenames
  my $byline = File::ByLine->new();
  $byline->file("file.txt")
  $byline->do( sub { foo($_) } );
  my (@grep_result) = $byline->grep( sub { m/foo/ } );
  my (@map_result)  = $byline->map( sub { lc($_) } );

=head1 DESCRIPTION

Finding myself writing the same trivial loops to read files, or relying on
modules like C<Perl6::Slurp> that didn't quite do what I needed (abstracting
the loop), it was clear something easy, simple, and sufficiently Perl-ish was
needed.

=head1 FUNCTIONS

=head2 dolines

  dolines { say "Line: $_" } "file.txt";
  dolines \&func, "file.txt";

This function calls a coderef once for each line in the file.  The file is read
line-by-line, removes the newline character(s), and then executes the coderef.

Each line (without newline) is passed to the coderef as the first parameter and
only parameter to the coderef.  It is also placed into C<$_>.

This function returns the number of lines in the file.

This is similar to C<forlines()>, except for order of arguments.  The author
recommends this form for short code blocks - I.E. a coderef that fits on
one line.  For longer, multi-line code blocks, the author recommends
the C<forlines()> syntax.

=head2 forlines

  forlines "file.txt", sub { say "Line: $_" };
  forlines "file.txt", \&func;

This function calls a coderef once for each line in the file.  The file is read
line-by-line, removes the newline character(s), and then executes the coderef.

Each line (without newline) is passed to the coderef as the first parameter and
only parameter to the coderef.  It is also placed into C<$_>.

This function returns the number of lines in the file.

This is similar to C<dolines()>, except for order of arguments.  The author
recommends this when using longer, multi-line code blocks, even though it is
not orthogonal with the C<maplines()>/C<greplines()> routines.

=head2 parallel_dolines

  my (@result) = parallel_dolines { foo($_) } "file.txt", 10;

Requires L<Parallel::WorkUnit> to be installed.

Three parameters are requied: a codref, a filename, and number of simultanious
child threads to use.

This function performs similar to C<dolines()>, except that it does its'
operations in parallel using C<fork()> and L<Parallel::WorkUnit>.  Because
the code in the coderef is executed in a child process, any changes it makes
to variables in high scopes will not be visible outside that single child.
In general, it will be safest to not modify anything that belongs outside
this scope.

Note that the file will be read in several chunks, with each chunk being
processed in a different thread.  This means that the child threads may be
operating on very different sections of the file simultaniously and no specific
order of execution of the coderef should be expected!

Because of the mechanism used to split the file into chunks for processing,
each thread may process a somewhat different number of lines.  This is
particularly true if there are a mix of very long and very short lines.  The
splitting routine splits the file into roughly equal size chunks by byte
count, not line count.

Otherwise, this function is identical to C<dolines()>.  See the documentation
for C<dolines()> or C<forlines()> for information about how this might differ
from C<parallel_forlines()>.

=head2 parallel_forlines

  my (@result) = parallel_forlines "file.txt", 10, sub { foo($_) };

Requires L<Parallel::WorkUnit> to be installed.

Three parameters are requied: a filename, a codref, and number of simultanious
child threads to use.

This function performs similar to C<forlines()>, except that it does its'
operations in parallel using C<fork()> and L<Parallel::WorkUnit>.  Because
the code in the coderef is executed in a child process, any changes it makes
to variables in high scopes will not be visible outside that single child.
In general, it will be safest to not modify anything that belongs outside
this scope.

Note that the file will be read in several chunks, with each chunk being
processed in a different thread.  This means that the child threads may be
operating on very different sections of the file simultaniously and no specific
order of execution of the coderef should be expected!

Because of the mechanism used to split the file into chunks for processing,
each thread may process a somewhat different number of lines.  This is
particularly true if there are a mix of very long and very short lines.  The
splitting routine splits the file into roughly equal size chunks by byte
count, not line count.

Otherwise, this function is identical to C<forlines()>.  See the documentation
for C<forlines()> or C<dolines()> for information about how this might differ
from C<parallel_dolines()>.

=head2 greplines

  my (@result) = greplines { m/foo/ } "file.txt";

Requires L<Parallel::WorkUnit> to be installed.

This function calls a coderef once for each line in the file, and, based on
the return value of that coderef, returns only the lines where the coderef
evaluates to true.  This is similar to the C<grep> built-in function, except
operating on file input rather than array input.

Each line (without newline) is passed to the coderef as the first parameter and
only parameter to the coderef.  It is also placed into C<$_>.

This function returns the lines for which the coderef evaluates as true.

=head2 parallel_greplines

  my (@result) = parallel_greplines { m/foo/ } "file.txt", 10;

Three parameters are requied: a coderef, filename, and number of simultanious
child threads to use.

This function performs similar to C<greplines()>, except that it does its'
operations in parallel using C<fork()> and L<Parallel::WorkUnit>.  Because
the code in the coderef is executed in a child process, any changes it makes
to variables in high scopes will not be visible outside that single child.
In general, it will be safest to not modify anything that belongs outside
this scope.

If a large amount of data is returned, the overhead of passing the data
from child to parents may exceed the benefit of parallelization.  However,
if there is substantial line-by-line processing, there likely will be a speedup,
but trivial loops will not speed up.

Note that the file will be read in several chunks, with each chunk being
processed in a different thread.  This means that the child threads may be
operating on very different sections of the file simultaniously and no specific
order of execution of the coderef should be expected!  However, the results
will be returned in the same order as C<greplines()> would return them.

Because of the mechanism used to split the file into chunks for processing,
each thread may process a somewhat different number of lines.  This is
particularly true if there are a mix of very long and very short lines.  The
splitting routine splits the file into roughly equal size chunks by byte
count, not line count.

Otherwise, this function is identical to C<greplines()>.

=head2 maplines

  my (@result) = maplines { lc($_) } "file.txt";

This function calls a coderef once for each line in the file, and, returns
an array of return values from those calls.  This follows normal Perl rules -
basically if the coderef returns a list, all elements of that list are added
as distinct elements to the return value array.  If the coderef returns an
empty list, no elements are added.

Each line (without newline) is passed to the coderef as the first parameter and
only parameter to the coderef.  It is also placed into C<$_>.

This is meant to be similar to the built-in C<map> function.

Because of the mechanism used to split the file into chunks for processing,
each thread may process a somewhat different number of lines.  This is
particularly true if there are a mix of very long and very short lines.  The
splitting routine splits the file into roughly equal size chunks by byte
count, not line count.

This function returns the lines for which the coderef evaluates as true.

=head2 parallel_maplines

  my (@result) = parallel_maplines { lc($_) } "file.txt", 10;

Three parameters are requied: a coderef, filename, and number of simultanious
child threads to use.

This function performs similar to C<maplines()>, except that it does its'
operations in parallel using C<fork()> and L<Parallel::WorkUnit>.  Because
the code in the coderef is executed in a child process, any changes it makes
to variables in high scopes will not be visible outside that single child.
In general, it will be safest to not modify anything that belongs outside
this scope.

If a large amount of data is returned, the overhead of passing the data
from child to parents may exceed the benefit of parallelization.  However,
if there is substantial line-by-line processing, there likely will be a speedup,
but trivial loops will not speed up.

Note that the file will be read in several chunks, with each chunk being
processed in a different thread.  This means that the child threads may be
operating on very different sections of the file simultaniously and no specific
order of execution of the coderef should be expected!  However, the results
will be returned in the same order as C<maplines()> would return them.

Otherwise, this function is identical to C<maplines()>.

=head2 readlines

  my (@result) = readlines "file.txt";

This function simply returns an array of lines (without newlines) read from
a file.

=head1 OBJECT ORIENTED INTERFACE

The object oriented interface was implemented in version 1.181860.

=head2 new

  my $byline = File::ByLine->new();

Constructs a new object, suitable for the object oriented calls below.

=head2 ATTRIBUTES

=head3 file

  my $current_file = $byline->file();
  $byline->file("abc.txt");

Gets and sets the default filename used by the methods in the object oriented
interface.  The default value is C<undef> which indicates that no default
filename is provided.

=head3 header_skip

  $byline->header_skip(1);

Gets and sets whether the object oriented methods will skip the first line
in the file (which you might want to do for a line that is a header).  This
defaults to false.  Any true value will cause the header line to be skipped.

You cannot set this to true while a C<header_handler> value is set.

=head3 header_handler

  $byline->header_handler( sub { ... } );

Specifies code that should be executed on the header row of the input file.
This defaults to C<undef>, which indicates no header handler is specified.
When a header handler is specified, the first row of the file is sent to this
handler, and is not sent to the code provided to the various do/grep/map/lines
methods in the object oriented interface.

The code is called with one parameter, the header line.  The header line is
also stored in C<$_>.

When set, this is always executed in the parent process, not in the child
processes that are spawned (in the case of C<processes> being greater than
one).

You cannot set this to true while a C<header_skip> value is set.

=head3 processes

  my $procs = $byline->processes();
  $byline->processes(10);

This gets and sets the degree of parallelism most methods will use.  The
default degree is C<1>, which indicates all tasks should only use a single
process.  Specifying C<2> or greater will use multiple processes to operate
on the file (see documentation for the parallel_* functions described above
for more details).

=head2 METHODS

=head3 do

  $byline->do( sub { ... }, "file.txt" );

This performs the C<dolines> functionality, calling the code provided.  If
the filename is not provided, the C<file> attribute is used for this.  See the
C<dolines> and C<parallel_dolines> functions for more information on how this
functions.

The code is called with one parameter, the header line.  The header line is
also stored in C<$_>.

=head3 grep

  my (@output) = $byline->grep( sub { ... }, "file.txt" );

This performs the C<greplines> functionality, calling the code provided.  If
the filename is not provided, the C<file> attribute is used for this.  See the
C<greplines> and C<parallel_greplines> functions for more information on how
this functions.

The code is called with one parameter, the header line.  The header line is
also stored in C<$_>.

The output is a list of all input lines where the code reference produces a
true result.

=head3 map

  my (@output) = $byline->map( sub { ... }, "file.txt" );

This performs the C<maplines> functionality, calling the code provided.  If
the filename is not provided, the C<file> attribute is used for this.  See the
C<maplines> and C<parallel_maplines> functions for more information on how
this functions.

The code is called with one parameter, the header line.  The header line is
also stored in C<$_>.

The output is the list produced by calling the passed-in code repeatively
for each line of input.

=head3 lines

  my (@output) = $byline->lines( "file.txt" );

This performs the C<readlines> functionality.  If the filename is not provided,
the C<file> attribute is used for this.  See the C<readlines> function for more
information on how this functions.

The output is a list of all input lines.

Note that this function is unaffected by the value of the C<processes>
attribute - it always executes in the parent process.

=head1 SUGGESTED DEPENDENCY

The L<Parallel::WorkUnit> module is a recommended dependency.  It is required
to use the C<parallel_*> functions - all other functionality works fine without
it.

Some CPAN clients will automatically try to install recommended dependency, but
others won't (L<cpan> often, but not always, will; L<cpanm> will not by
default).  In the cases where it is not automatically installed, you need to
install L<Parallel::WorkUnit> to get this functionality.

=head1 AUTHOR

Joelle Maslak <jmaslak@antelope.net>

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2018 by Joelle Maslak.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut