07-14-2010
It simply uses extended regular expressions by default instead of basic regular expressions. You can do the same with 'grep -E'.
In extended regular expressions, parenthesis are metacharactes which are used for grouping and capturing; thus, they must be escaped if they are to be matched literally. In basic regular expressions, the parenthesis are not metacharacters and must be quoted if they are to be used to capture or group.
Although egrep defaults to using a more powerful regular expression language, the command itself is not in any way more robust ... imo.
Regards,
Alister
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LEARN ABOUT OPENSOLARIS
re_comp
re_comp(3C) Standard C Library Functions re_comp(3C)
NAME
re_comp, re_exec - compile and execute regular expressions
SYNOPSIS
#include <re_comp.h>
char *re_comp(const char *string);
int re_exec(const char *string);
DESCRIPTION
The re_comp() function converts a regular expression string (RE) into an internal form suitable for pattern matching. The re_exec() func-
tion compares the string pointed to by the string argument with the last regular expression passed to re_comp().
If re_comp() is called with a null pointer argument, the current regular expression remains unchanged.
Strings passed to both re_comp() and re_exec() must be terminated by a null byte, and may include NEWLINE characters.
The re_comp() and re_exec() functions support simple regular expressions, which are defined on the regexp(5) manual page. The regular
expressions of the form {m}, {m,}, or {m,n} are not supported.
RETURN VALUES
The re_comp() function returns a null pointer when the string pointed to by the string argument is successfully converted. Otherwise, a
pointer to one of the following error message strings is returned:
No previous regular expression
Regular expression too long
unmatched (
missing ]
too many () pairs
unmatched )
Upon successful completion, re_exec() returns 1 if string matches the last compiled regular expression. Otherwise, re_exec() returns 0 if
string fails to match the last compiled regular expression, and -1 if the compiled regular expression is invalid (indicating an internal
error).
ERRORS
No errors are defined.
USAGE
For portability to implementations conforming to X/Open standards prior to SUS, regcomp(3C) and regexec(3C) are preferred to these func-
tions. See standards(5).
SEE ALSO
grep(1), regcmp(1), regcmp(3C), regcomp(3C), regexec(3C), regexpr(3GEN), regexp(5), standards(5)
SunOS 5.11 26 Feb 1997 re_comp(3C)