File: gawk.info,  Node: Fields with fixed data,  Prev: Allowing trailing data,  Up: Constant Size

4.6.4 Field Values With Fixed-Width Data
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So far, so good.  But what happens if there isn't as much data as there
should be based on the contents of 'FIELDWIDTHS'?  Or, what happens if
there is more data than expected?

   For many years, what happens in these cases was not well defined.
Starting with version 4.2, the rules are as follows:

Enough data for some fields
     For example, if 'FIELDWIDTHS' is set to '"2 3 4"' and the input
     record is 'aabbb'.  In this case, 'NF' is set to two.

Not enough data for a field
     For example, if 'FIELDWIDTHS' is set to '"2 3 4"' and the input
     record is 'aab'.  In this case, 'NF' is set to two and '$2' has the
     value '"b"'.  The idea is that even though there aren't as many
     characters as were expected, there are some, so the data should be
     made available to the program.

Too much data
     For example, if 'FIELDWIDTHS' is set to '"2 3 4"' and the input
     record is 'aabbbccccddd'.  In this case, 'NF' is set to three and
     the extra characters ('ddd') are ignored.  If you want 'gawk' to
     capture the extra characters, supply a final '*' in the value of
     'FIELDWIDTHS'.

Too much data, but with '*' supplied
     For example, if 'FIELDWIDTHS' is set to '"2 3 4 *"' and the input
     record is 'aabbbccccddd'.  In this case, 'NF' is set to four, and
     '$4' has the value '"ddd"'.