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=head2 csv_sort_fields_by_spec

Usage:

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

Sort CSV fields by spec.

This is a thin wrapper for L<csv-sort-fields> to allow you to sort "by
spec". Sorting by spec is an advanced form of sorting by example. In addition to
specifying strings of examples, you can also specify regexes or Perl sorter
codes. For more details, see the sorting backend module L<Sort::BySpec>.

To specify a regex on the command-line, use one of these forms:

 /.../
 qr(...)

and to specify Perl code on the command-line, use this form:

 sub { ... }

For example, modifying from example in C<Sort::BySpec>'s Synopsis, you want to
sort these fields:

 field1..field15 field42

as follow: 1) put fields with odd numbers first in ascending order; 2) put the
specific fields field4, field2, field42 in that order; 3) put the remaining
fields of even numbers in descending order. To do this:

 % perl -E'say join(",",map {"field$_"} 1..15,42)' | csv-sort-fields-by-spec - \
     'qr([13579]\z)' 'sub { my($a,$b)=@_; for($a,$b){s/field//} $a<=>$b }' \
     field4 field2 field42 \
     'sub { my($a,$b)=@_; for($a,$b){s/field//} $b<=>$a }'

The result:

 field1,field3,field5,field7,field9,field11,field13,field15,field4,field2,field42,field14,field12,field10,field8,field6

This function is not exported.

Arguments ('*' denotes required arguments):

=over 4

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

(No description)

=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>

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

Defaults to C<,> (comma). Overrides C<--input-tsv> option.

=item * B<input_skip_num_lines> => I<posint>

Number of lines to skip before header row.

This can be useful if you have a CSV files (usually some generated reports,
sometimes converted from spreadsheet) that have additional header lines or info
before the CSV header row.

See also the alternative option: C<--input-skip-until-pattern>.

=item * B<input_skip_until_pattern> => I<re_from_str>

Skip rows until the first header row matches a regex pattern.

This is an alternative to the C<--input-skip-num-lines> and can be useful if you
have a CSV files (usually some generated reports, sometimes converted from
spreadsheet) that have additional header lines or info before the CSV header
row.

With C<--input-skip-num-lines>, you skip a fixed number of lines. With this
option, rows will be skipped until the first field matches the specified regex
pattern.