No, expr and egrep do not use the same types of regular expression. Although some man pages aren't very clear about what form of regular expressions are used by expr match string pattern and expr string : pattern, the standards are clear:
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The ':' matching operator shall compare the string resulting from the
evaluation of expr1 with the regular expression pattern resulting from
the evaluation of expr2. Regular expression syntax shall be that
defined in the Base Definitions volume of IEEE Std 1003.1-2001, Section
9.3, Basic Regular Expressions, except that all patterns are anchored
to the beginning of the string (that is, only sequences starting at the
first character of a string are matched by the regular expression) and,
therefore, it is unspecified whether '^' is a special character in that
context. Usually, the matching operator shall return a string repre-
senting the number of characters matched ( '0' on failure). Alterna-
tively, if the pattern contains at least one regular expression subex-
pression "[\(...\)]" , the string corresponding to "\1" shall be
returned.
Note that the match string pattern form is not in the standards; it is an extension supported on some (but not all) systems.
The egrep (which is obsolete) and the equivalent grep -E commands use extended regular expressions. The description of grep's regular expressions in POSIX is:
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Regular expression matching shall be based on text lines. Since a <newline> separates or
terminates patterns (see the −e and −f options below), regular expressions cannot contain a
<newline>. Similarly, since patterns are matched against individual lines (excluding the
terminating <newline> characters) of the input, there is no way for a pattern to match a
<newline> found in the input.
and
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-E Match using extended regular expressions. Treat each pattern
specified as an ERE, as described in the Base Definitions volume
of IEEE Std 1003.1-2001, Section 9.4, Extended Regular Expres-
sions. If any entire ERE pattern matches some part of an input
line excluding the terminating <newline>, the line shall be
matched. A null ERE shall match every line.
You don't need to backslash-escape characters in a bracket expression in an RE. If you do, the backslash character itself becomes a member of the set of characters to be matched by a matching bracket expression or to be excluded from the list of characters to be matched by a non-matching bracket expression.
This User Gave Thanks to Don Cragun For This Post:
Hi
I want to do a regex test and branch based on the test result, but this doesn't seems to work :confused:
if \) ]]
then
echo success
else
echo failed
fi (1 Reply)
It can get very annoying that bash regex =~ is case-sensetive, is there a way to set it to be case-insensetive?
if ]; then
echo match
else
echo no match
fi (8 Replies)
Hello
I have a bash script where I need to do a substring replacement like this:
variable2=${variable1/foo/bar}
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Hey all,
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I've been using the following regex below in a bash script on RHEL 5.5 using version
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I can use if -2014 ]]; then echo "yes";fi
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