FAQ 4.34 How do I extract selected columns from a string?

P

PerlFAQ Server

This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

--------------------------------------------------------------------

4.34: How do I extract selected columns from a string?

(contributed by brian d foy)

If you know the columns that contain the data, you can use "substr" to
extract a single column.

my $column = substr( $line, $start_column, $length );

You can use "split" if the columns are separated by whitespace or some
other delimiter, as long as whitespace or the delimiter cannot appear as
part of the data.

my $line = ' fred barney betty ';
my @columns = split /\s+/, $line;
# ( '', 'fred', 'barney', 'betty' );

my $line = 'fred||barney||betty';
my @columns = split /\|/, $line;
# ( 'fred', '', 'barney', '', 'betty' );

If you want to work with comma-separated values, don't do this since
that format is a bit more complicated. Use one of the modules that
handle that format, such as "Text::CSV", "Text::CSV_XS", or
"Text::CSV_PP".

If you want to break apart an entire line of fixed columns, you can use
"unpack" with the A (ASCII) format. By using a number after the format
specifier, you can denote the column width. See the "pack" and "unpack"
entries in perlfunc for more details.

my @fields = unpack( $line, "A8 A8 A8 A16 A4" );

Note that spaces in the format argument to "unpack" do not denote
literal spaces. If you have space separated data, you may want "split"
instead.



--------------------------------------------------------------------

The perlfaq-workers, a group of volunteers, maintain the perlfaq. They
are not necessarily experts in every domain where Perl might show up,
so please include as much information as possible and relevant in any
corrections. The perlfaq-workers also don't have access to every
operating system or platform, so please include relevant details for
corrections to examples that do not work on particular platforms.
Working code is greatly appreciated.

If you'd like to help maintain the perlfaq, see the details in
perlfaq.pod.
 

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.

Ask a Question

Members online

No members online now.

Forum statistics

Threads
473,717
Messages
2,569,382
Members
44,704
Latest member
FawnBernay

Latest Threads

Top