Appending a pattern to a preexisting regex

jp flag

I have this regex that allows a space followed by visible characters


How can I construct the possibilities of having either some pattern ptrn or the same pattern ptrn followed by the additional one above?

Max Ballard avatar
id flag
This is better suited for or
hr flag

Awk uses POSIX extended regular expressions, so you can use ? as a quantifier to represent either zero or one occurrence of the preceding pattern:

$ printf '%s\n' 'ptrn' 'foo bar' 'ptrn bar' | awk '/ptrn([[:space:]][[:graph:]]+)?$/'
ptrn bar

In GNU awk aka gawk you can also use a {n,m} quantifier:

$ printf '%s\n' 'ptrn' 'foo bar' 'ptrn bar' | gawk '/ptrn([[:space:]][[:graph:]]+){0,1}$/'
ptrn bar
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