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=head2 csv_grep

Usage:

 csv_grep(%args) -> [$status_code, $reason, $payload, \%result_meta]

Select (only output) row(s) where Perl expression returns true.

Examples:

=over

=item * Only show rows where the amount field is divisible by 7:

 csv_grep(
     input_filename => "file.csv",
   eval => "\$_->{amount} % 7 == 0",
   hash => 1
 );

=item * Only show rows where date is a Wednesday:

 csv_grep(
     input_filename => "file.csv",
   eval => "BEGIN { use DateTime::Format::Natural; \$parser = DateTime::Format::Natural->new } \$dt = \$parser->parse_datetime(\$_->{date}); \$dt->day_of_week == 3",
   hash => 1
 );

=back

This is like Perl's C<grep> performed over rows of CSV. In C<$_>, your Perl code
will find the CSV row as an arrayref (or, if you specify C<-H>, as a hashref).
C<$main::row> is also set to the row (always as arrayref). C<$main::rownum>
contains the row number (2 means the first data row). C<$main::csv> is the
L<Text::CSV_XS> object. C<$main::fields_idx> is also available for additional
information.

Your code is then free to return true or false based on some criteria. Only rows
where Perl expression returns true will be included in the result.

This function is not exported.

Arguments ('*' denotes required arguments):

=over 4

=item * B<eval>* => I<str|code>

Perl code.

=item * B<hash> => I<bool>

Provide row in $_ as hashref instead of arrayref.

=item * B<inplace> => I<true>

Output to the same file as input.

Normally, you output to a different file than input. If you try to output to the
same file (C<-o INPUT.csv -O>) you will clobber the input file; thus the utility
prevents you from doing it. However, with this C<--inplace> option, you can
output to the same file. Like perl's C<-i> option, this will first output to a
temporary file in the same directory as the input file then rename to the final
file at the end. You cannot specify output file (C<-o>) when using this option,
but you can specify backup extension with C<-b> option.

Some caveats:

=over

=item * if input file is a symbolic link, it will be replaced with a regular file;

=item * renaming (implemented using C<rename()>) can fail if input filename is too long;

=item * value specified in C<-b> is currently not checked for acceptable characters;

=item * things can also fail if permissions are restrictive;

=back

=item * B<inplace_backup_ext> => I<str> (default: "")

Extension to add for backup of input file.

In inplace mode (C<--inplace>), if this option is set to a non-empty string, will
rename the input file using this extension as a backup. The old existing backup
will be overwritten, if any.

=item * B<input_escape_char> => I<str>

Specify character to escape value in field in input CSV, will be passed to Text::CSV_XS.

Defaults to C<\\> (backslash). Overrides C<--input-tsv> option.

=item * B<input_filename> => I<filename> (default: "-")

Input CSV file.

Use C<-> to read from stdin.

Encoding of input file is assumed to be UTF-8.

=item * B<input_header> => I<bool> (default: 1)

Specify whether input CSV has a header row.

By default, the first row of the input CSV will be assumed to contain field
names (and the second row contains the first data row). When you declare that
input CSV does not have header row (C<--no-input-header>), the first row of the
CSV is assumed to contain the first data row. Fields will be named C<field1>,
C<field2>, and so on.

=item * B<input_quote_char> => I<str>

Specify field quote character in input CSV, will be passed to Text::CSV_XS.

Defaults to C<"> (double quote). Overrides C<--input-tsv> option.

=item * B<input_sep_char> => I<str>