gawk: Fields with fixed data
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"'.
Info Catalog
gawk: Allowing trailing data
gawk: Constant Size