Repetition takes precedence over concatenation, which in
turn takes precedence over alternation. A whole subex-
pression may be enclosed in parentheses to override these
precedence rules.
The backreference n, where n is a single digit, matches
the substring previously matched by the nth parenthesized
|, (, and ) lose their special meaning; instead use the
backslashed versions ?, +, {, |, (, and ).
In egrep the metacharacter { loses its special meaning;
instead use {.
