Ben Tilly > Text-xSV-0.18 > Text::xSV

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Module Version: 0.18   Source   Latest Release: Text-xSV-0.21

NAME ^

Text::xSV - read character separated files

SYNOPSIS ^

  use Text::xSV;
  my $csv = new Text::xSV;
  $csv->open_file("foo.csv");
  $csv->read_header();
  # Make the headers case insensitive
  foreach my $field ($csv->get_fields) {
    if (lc($field) ne $field) {
      $csv->alias($field, lc($field));
    }
  }
  
  $csv->add_compute("message", sub {
    my $csv = shift;
    my ($name, $age) = $csv->extract(qw(name age));
    return "$name is $age years old\n";
  });

  while ($csv->get_row()) {
    my ($name, $age) = $csv->extract(qw(name age));
    print "$name is $age years old\n";
    # Same as
    #   print $csv->extract("message");
  }

  # The file above could have been created with:
  my $csv = Text::xSV->new(
    filename => "foo.csv",
    header   => ["Name", "Age", "Sex"],
  );
  $csv->print_header();
  $csv->print_row("Ben Tilly", 34, "M");
  # Same thing.
  $csv->print_data(
    Age  => 34,
    Name => "Ben Tilly",
    Sex  => "M",
  );

DESCRIPTION ^

This module is for reading and writing a common variation of character separated data. The most common example is comma-separated. However that is far from the only possibility, the same basic format is exported by Microsoft products using tabs, colons, or other characters.

The format is a series of rows separated by returns. Within each row you have a series of fields separated by your character separator. Fields may either be unquoted, in which case they do not contain a double-quote, separator, or return, or they are quoted, in which case they may contain anything, and will encode double-quotes by pairing them. In Microsoft products, quoted fields are strings and unquoted fields can be interpreted as being of various datatypes based on a set of heuristics. By and large this fact is irrelevant in Perl because Perl is largely untyped. The one exception that this module handles that empty unquoted fields are treated as nulls which are represented in Perl as undefined values. If you want a zero-length string, quote it.

People usually naively solve this with split. A next step up is to read a line and parse it. Unfortunately this choice of interface (which is made by Text::CSV on CPAN) makes it difficult to handle returns embedded in a field. (Earlier versions of this document claimed impossible. That is false. But the calling code has to supply the logic to add lines until you have a valid row. To the extent that you don't do this consistently, your code will be buggy.) Therefore you it is good for the parsing logic to have access to the whole file.

This module solves the problem by creating a CSV object with access to the filehandle, if in parsing it notices that a new line is needed, it can read at will.

USAGE ^

First you set up and initialize an object, then you read the CSV file through it. The creation can also do multiple initializations as well. Here are the available methods

new

This is the constructor. It takes a hash of optional arguments. They correspond to the following set_* methods without the set_ prefix. For instance if you pass filename=>... in, then set_filename will be called.

set_sep

Sets the one character separator that divides fields. Defaults to a comma.

set_filename

The filename of the xSV file that you are reading. Used heavily in error reporting. If fh is not set and filename is, then fh will be set to the result of calling open on filename.

set_fh

Sets the fh that this Text::xSV object will read from or write to. If it is not set, it will be set to the result of opening filename if that is set, otherwise it will default to ARGV (ie acts like <>) or STDOUT, depending on whether you first try to read or write. The old default used to be STDIN.

set_header

Sets the internal header array of fields that is referred to in arranging data on the *_data output methods. If bind_fields has not been called, also calls that on the assumption that the fields that you want to output matches the fields that you will provide.

The return from this function is inconsistent and should not be relied on to be anything useful.

set_headers

An alias to set_header.

set_error_handler

The error handler is an anonymous function which is expected to take an error message and do something useful with it. The default error handler is Carp::confess. Error handlers that do not trip exceptions (eg with die) are less tested and may not work perfectly in all circumstances.

set_warning_handler

The warning handler is an anonymous function which is expected to take a warning and do something useful with it. If no warning handler is supplied, the error handler is wrapped with eval and the trapped error is warned.

set_filter

The filter is an anonymous function which is expected to accept a line of input, and return a filtered line of output. The default filter removes \r so that Windows files can be read under Unix. This could also be used to, eg, strip out Microsoft smart quotes.

set_row_size

The number of elements that you expect to see in each row. It defaults to the size of the first row read or set. If row_size_warning is true and the size of the row read or formatted does not match, then a warning is issued.

set_row_size_warning

Determines whether or not to issue warnings when the row read or set has a number of fields different than the expected number. Defaults to true. Whether or not this is on, missing fields are always read as undef, and extra fields are ignored.

set_close_fh

Whether or not to close fh when the object is DESTROYed. Defaults to false if fh was passed in, or true if the object has to open its own fh. (This may be removed in a future version.)

open_file

Takes the name of a file, opens it, then sets the filename and fh.

bind_fields

Takes an array of fieldnames, memorizes the field positions for later use. read_header is preferred.

read_header

Reads a row from the file as a header line and memorizes the positions of the fields for later use. File formats that carry field information tend to be far more robust than ones which do not, so this is the preferred function.

read_headers

An alias for read_header. (If I'm going to keep on typing the plural, I'll just make it work...)

bind_header

Another alias for read_header maintained for backwards compatibility. Deprecated because the name doesn't distinguish it well enough from the unrelated set_header.

get_row

Reads a row from the file. Returns an array or reference to an array depending on context. Will also store the row in the row property for later access.

extract

Extracts a list of fields out of the last row read. In list context returns the list, in scalar context returns an anonymous array.

extract_hash

Extracts fields into a hash. If a list of fields is passed, that is the list of fields that go into the hash. If no list, it extracts all fields that it knows about. In list context returns the hash. In scalar context returns a reference to the hash.

fetchrow_hash

Combines get_row and extract_hash to fetch the next row and return a hash or hashref depending on context.

alias

Makes an existing field available under a new name.

  $csv->alias($old_name, $new_name);
get_fields

Returns a list of all known fields in no particular order.

add_compute

Adds an arbitrary compute. A compute is an arbitrary anonymous function. When the computed field is extracted, Text::xSV will call the compute in scalar context with the Text::xSV object as the only argument.

Text::xSV caches results in case computes call other computes. It will also catch infinite recursion with a hopefully useful message.

format_row

Takes a list of fields, and returns them quoted as necessary, joined with sep, with a newline at the end.

format_header

Returns the formatted header row based on what was submitted with set_header. Will cause an error if set_header was not called.

format_headers

Continuing the meme, an alias for format_header.

format_data

Takes a hash of data. Sets internal data, and then formats the result of extracting out the fields corresponding to the headers. Note that if you called bind_fields and then defined some more fields with add_compute, computes would be done for you on the fly.

print

Prints the arguments directly to fh. If fh is not supplied but filename is, first sets fh to the result of opening filename. Otherwise it defaults fh to STDOUT. You probably don't want to use this directly. Instead use one of the other print methods.

print_row

Does a print of format_row. Convenient when you wish to maintain your knowledge of the field order.

print_header

Does a print of format_header. Makes sense when you will be using print_data for your actual data because the field order is guaranteed to match up.

print_headers

An alias to print_header.

print_data

Does a print of format_data. Relieves you from having to synchronize field order in your code.

TODO ^

Add utility interfaces. (Suggested by Ken Clark.)

Offer an option for working around the broken tab-delimited output that some versions of Excel present for cut-and-paste.

Add tests for the output half of the module.

BUGS ^

When I say single character separator, I mean it.

Performance could be better. That is largely because the API was chosen for simplicity of a "proof of concept", rather than for performance. One idea to speed it up you would be to provide an API where you bind the requested fields once and then fetch many times rather than binding the request for every row.

Also note that should you ever play around with the special variables $`, $&, or $', you will find that it can get much, much slower. The cause of this problem is that Perl only calculates those if it has ever seen one of those. This does many, many matches and calculating those is slow.

I need to find out what conversions are done by Microsoft products that Perl won't do on the fly upon trying to use the values.

ACKNOWLEDGEMENTS ^

My thanks to people who have given me feedback on how they would like to use this module, and particularly to Klaus Weidner for his patch fixing a nasty segmentation fault from a stack overflow in the regular expression engine on large fields.

Rob Kinyon (dragonchild) motivated me to do the writing interface, and gave me useful feedback on what it should look like. I'm not sure that he likes the result, but it is how I understood what he said...

Jess Robinson (castaway) convinced me that ARGV was a better default input handle than STDIN. I hope that switching that default doesn't inconvenience anyone.

Gyepi SAM noticed that fetchrow_hash complained about missing data at the end of the loop and sent a patch. Applied.

shotgunefx noticed that bind_header changed its return between versions. It is actually worse than that, it changes its return if you call it twice. Documented that its return should not be relied upon.

Fred Steinberg found that writes did not happen promptly upon closing the object. This turned out to be a self-reference causing a DESTROY bug. I fixed it.

Carey Drake and Steve Caldwell noticed that the default warning_handler expected different arguments than it got. Both suggested the same fix that I implemented.

AUTHOR AND COPYRIGHT ^

Ben Tilly (btilly@gmail.com). Originally posted at http://www.perlmonks.org/node_id=65094.

Copyright 2001-2009. This may be modified and distributed on the same terms as Perl.

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