Learning AWK Programming

Positive closure

The positive closure or plus (+) means that the item immediately preceded by + is matched one or more times. For example, the ca+t would match cat and caat, whereas ca*t would match all three, as follows:

$ echo -e "cat\nct\ncaat\ncbt" | awk '/ca+t/'

The output on execution of the preceding code is as follows:

catcaat

A summary of positive closure (+) is as follows:

Pattern	Matches
A+	Matches the single A, AA, or AAA, and so on
AB+C	Matches ABC, ABBC, or ABBBC, and so on
[0-9]+	Matches one or more numbers
[0-9][0-9]+	Matches two or more numbers
^A+	Matches any line beginning with one or more A letters
^A\+	Matches any line starting with A+
^AA+	Matches any line starting with ...