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File-ByLine-1.181861
River stage one • 1 direct dependent • 1 total dependent
3 ++
/ File::ByLine

NAME

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

VERSION

version 1.181861

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)  = $byline->map( sub { lc($_) } );

DESCRIPTION

Finding myself writing the same trivial loops to read files, or relying on modules like 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.

FUNCTIONS

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 $_.

This function returns the number of lines in the file.

This is similar to 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 forlines() syntax.

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 $_.

This function returns the number of lines in the file.

This is similar to 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 maplines()/greplines() routines.

parallel_dolines

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

Requires 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 dolines(), except that it does its' operations in parallel using fork() and 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 dolines(). See the documentation for dolines() or forlines() for information about how this might differ from parallel_forlines().

parallel_forlines

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

Requires 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 forlines(), except that it does its' operations in parallel using fork() and 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 forlines(). See the documentation for forlines() or dolines() for information about how this might differ from parallel_dolines().

greplines

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

Requires 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 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 $_.

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

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 greplines(), except that it does its' operations in parallel using fork() and 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 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 greplines().

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 $_.

This is meant to be similar to the built-in 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.

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 maplines(), except that it does its' operations in parallel using fork() and 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 maplines() would return them.

Otherwise, this function is identical to maplines().

readlines

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

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

OBJECT ORIENTED INTERFACE

The object oriented interface was implemented in version 1.181860.

new

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

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

ATTRIBUTES

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 undef which indicates that no default filename is provided.

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 header_handler value is set.

header_handler

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

Specifies code that should be executed on the header row of the input file. This defaults to 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 $_.

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

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

processes

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

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

METHODS

do

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

This performs the dolines functionality, calling the code provided. If the filename is not provided, the file attribute is used for this. See the dolines and 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 $_.

grep

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

This performs the greplines functionality, calling the code provided. If the filename is not provided, the file attribute is used for this. See the greplines and 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 $_.

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

map

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

This performs the maplines functionality, calling the code provided. If the filename is not provided, the file attribute is used for this. See the maplines and 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 $_.

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

lines

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

This performs the readlines functionality. If the filename is not provided, the file attribute is used for this. See the 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 processes attribute - it always executes in the parent process.

SUGGESTED DEPENDENCY

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

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

AUTHOR

Joelle Maslak <jmaslak@antelope.net>

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.