To begin with your concrete example ...

The specification looks something like -- fieldA is from character 9 to 14
my $TEMPLATE = '@8A6'; # oops, originally posted without the quotes  
while (<DATA>) {
    my @fields = unpack $TEMPLATE, $_;
 
    # for output try pack or printf
}

[download]

This generalizes. The template for unpack should be machine-generated, to avoid off-by-one errors and other typos.

In what follows, let's suppose you have collected a list of column specifications. Each specification tells you

You might get this from a config file of some sort, or as the result set from a database query, if you happen to have saved your parse specifications in a database table.

use DBI;
my $dbh = ...
my $sth = $dbh->prepare(
    'SELECT field, offset, width'
    . ' FROM Source_Field'
    . ' WHERE source = ?;'
);
my $source = 'input_file.txt';
$sth->execute($source);
my $template;
my @fields;
while (my $column_spec = $sth->fetchrow_hashref() ) {
    my ($field, $offset, $width) 
        = @$column_spec{qw(field offset width)};
    $template .= "\@${offset}A$width";
    push @fields, $field;
}
open my $reader, '<', $source;
while (<$reader>) {
    my %value_of;
    my @values = unpack($template, $_);
    @value_of{@fields} = @values;

    # you've got your current record in a hash
    # print it or save it somewhere
}

[download]

In reply to Re: framework for data parsing by Narveson
in thread framework for data parsing by sam700

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.