Re: Quick grep question

On Mon, 27 Feb 2006 13:17:19 -0500, Chris F.A. Johnson wrote:
On 2006-02-27, Samik R wrote:
Hello,

I am trying to match couple of lines using grep. Assuming my file
has following 3 lines:
inx23r678
inx34r54
inx23_44

I want the lines with inx<some digits>r<some digits>, not the
underscore ones. I am trying this:
cat file|grep "inx[0-9]+r"
which is not working. But,
cat file|grep "inx[0-9]*r"

is working. I thought '+' matches with 1 or more occurrences, so the
first one should work too. Where am I going wrong?

First, you don't need cat; second, you need to escape the plus
sign:

grep "inx[0-9]\+r" file
[...]

Neither + nor \+ are BRE operators, so are not supposed to work
with grep. Some grep implementations such as GNU grep recognise
\+ as an extension.

What is standard BRE is \{1,\} (one or more occurrences of the
previous pattern).

+ is a standard ERE operator, -E is a standard option to grep to
understand a pattern as an ERE.

--
Stephane
.

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