File: gawk.info,  Node: Field Splitting Summary,  Prev: Full Line Fields,  Up: Field Separators

4.5.6 Field-Splitting Summary
-----------------------------

It is important to remember that when you assign a string constant as
the value of 'FS', it undergoes normal 'awk' string processing.  For
example, with Unix 'awk' and 'gawk', the assignment 'FS = "\.."' assigns
the character string '".."' to 'FS' (the backslash is stripped).  This
creates a regexp meaning "fields are separated by occurrences of any two
characters."  If instead you want fields to be separated by a literal
period followed by any single character, use 'FS = "\\.."'.

   The following list summarizes how fields are split, based on the
value of 'FS' ('==' means "is equal to"):

'FS == " "'
     Fields are separated by runs of whitespace.  Leading and trailing
     whitespace are ignored.  This is the default.

'FS == ANY OTHER SINGLE CHARACTER'
     Fields are separated by each occurrence of the character.  Multiple
     successive occurrences delimit empty fields, as do leading and
     trailing occurrences.  The character can even be a regexp
     metacharacter; it does not need to be escaped.

'FS == REGEXP'
     Fields are separated by occurrences of characters that match
     REGEXP.  Leading and trailing matches of REGEXP delimit empty
     fields.

'FS == ""'
     Each individual character in the record becomes a separate field.
     (This is a common extension; it is not specified by the POSIX
     standard.)

                         'FS' and 'IGNORECASE'

   The 'IGNORECASE' variable (*note User-modified::) affects field
splitting _only_ when the value of 'FS' is a regexp.  It has no effect
when 'FS' is a single character, even if that character is a letter.
Thus, in the following code:

     FS = "c"
     IGNORECASE = 1
     $0 = "aCa"
     print $1

The output is 'aCa'.  If you really want to split fields on an
alphabetic character while ignoring case, use a regexp that will do it
for you (e.g., 'FS = "[c]"').  In this case, 'IGNORECASE' will take
effect.