gawk: Default Field Splitting
4.5.1 Whitespace Normally Separates Fields
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Fields are normally separated by whitespace sequences (spaces, TABs, and
newlines), not by single spaces. Two spaces in a row do not delimit an
empty field. The default value of the field separator 'FS' is a string
containing a single space, '" "'. If 'awk' interpreted this value in
the usual way, each space character would separate fields, so two spaces
in a row would make an empty field between them. The reason this does
not happen is that a single space as the value of 'FS' is a special
case--it is taken to specify the default manner of delimiting fields.
If 'FS' is any other single character, such as '","', then each
occurrence of that character separates two fields. Two consecutive
occurrences delimit an empty field. If the character occurs at the
beginning or the end of the line, that too delimits an empty field. The
space character is the only single character that does not follow these
rules.
Info Catalog
gawk: Field Separators
gawk: Regexp Field Splitting