gawk: Full Line Fields
4.5.5 Making the Full Line Be a Single Field
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Occasionally, it's useful to treat the whole input line as a single
field. This can be done easily and portably simply by setting 'FS' to
'"\n"' (a newline):(1)
awk -F'\n' 'PROGRAM' FILES ...
When you do this, '$1' is the same as '$0'.
Changing 'FS' Does Not Affect the Fields
According to the POSIX standard, 'awk' is supposed to behave as if
each record is split into fields at the time it is read. In particular,
this means that if you change the value of 'FS' after a record is read,
the values of the fields (i.e., how they were split) should reflect the
old value of 'FS', not the new one.
However, many older implementations of 'awk' do not work this way.
Instead, they defer splitting the fields until a field is actually
referenced. The fields are split using the _current_ value of 'FS'!
(d.c.) This behavior can be difficult to diagnose. The following
example illustrates the difference between the two methods:
sed 1q /etc/passwd | awk '{ FS = ":" ; print $1 }'
which usually prints:
root
on an incorrect implementation of 'awk', while 'gawk' prints the full
first line of the file, something like:
root:x:0:0:Root:/:
(The 'sed'(2) command prints just the first line of '/etc/passwd'.)
---------- Footnotes ----------
(1) Thanks to Andrew Schorr for this tip.
(2) The 'sed' utility is a "stream editor." Its behavior is also
defined by the POSIX standard.
Info Catalog
gawk: Command Line Field Separator
gawk: Field Separators
gawk: Field Splitting Summary