grep and egrep regular expressions, decreasing order of precedence (Kernighan and Pike 1984 The UNIX Programming Environment:105)
| c | any non-special character c matches itself |
| \c | turn off any special meaning of character c |
| ^ | beginning of line |
| \ | send of line |
| . | any single character |
| [...] | any one of the characters in ...; ranges like a-z are legal |
| [^...] | any single character not in ...; ranges are legal |
| \n | what the nth \(...\) matched (grep only) |
| r* | zero ore more occurrences of r |
| r+ | one or more occurrences of r (egrep only) |
| r? | zero or one occurrences of r (egrep only) |
| r1r2 | r1 followed by r2 |
| r1|r2 | r1 or r2 (egrep only) |
| \(r\) | tagged regular expression r (grep only); can be nested |
| (r) | regular expression r (egrep only); can be nested |
| No regular expression matches a newline. |