Question

 echo xx y11y rrr | awk '{ if ($2 ~/y[1-5]{2}y/) print $3}'

Why I cannot get any output?

Thank you.

Answer 1

You need to enable “interval expressions” in regular expression matching by specifying either the --posix or --re-interval option.

e.g.

echo xx y11y rrr | awk --re-interval '{ if ($2 ~ /y[1-5]{2}y/) print $3}

From the man page:

–re-interval
Enable the use of interval expressions in regular expression matching (see Regular Expressions, below). Interval expressions were
not traditionally available in
the AWK language. The POSIX standard added them, to make awk and egrep consistent with each other. However, their use is
likely to break old AWK programs, so
gawk only provides them if they are requested with this option, or when –posix is specified.