All right, so here's an example:
grep -E "1{2}" file.txt (red means match)
111111111000
00011
11100

I expected 1{2} or 1\{2\} (whatever) to match only "1" only twice. In the first sentence, it seems to match 8 1s. The second should be correct, and the third, again, it's correct.

If I write:
grep -E "1{1}" file.txt, the third string (11100) shows up like this:
11100

So there are three 1s highlighted.
I don't really understand what's going on. It seems to work as the minium, as if I also wrote the comma after the number of occurences, instead of a fixed value.

What do I not understand?

grep -E "1{2}" file.txt
because 11 was found 4 times and all the 4 occurrences were coloured.

grep -E "1{1}" file.txt
1 was found 3 times...

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Right, it makes perfect sense. Thanks.

Here is an example demonstrating the first point:
Again, all groups of 2 will be highlighted

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Another question, if we're at it:
grep -E "(Labs ){2}" lab.txt
Labs Labs Labs

But grep -E "(Labs ){3}" lab.txt displays nothing. Why?

You included the trailing space in the match, and apparently the line does not have a space at the end.

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Yeah, that was simple Thanks.

And if I wanted it to match all, then I'd do: grep -E "(Labs ?){3}"

That's certainly one way to do it. Without knowing your overall objective, this starts to resemble an "X-Y problem".

The overall objective is simply understanding (extended) regex better, and go on to learn awk, sed better.

HEY YOU!(just getting your attention) mine didn't get highlighted.

they just printed out as if I just wrote them again is all.

sooooo how would one fix that. or make it so that one could actually tell that did what someone thought they told to do.
no color was added.
whats really going on here?
Inquiring minds want to know.

I think the highlight is just a shell option (or a terminal option, maybe?). But I don't think it's something a real sysadmin should count on I'm just trying to profit from it, 'cause it's there.

I'm using the macos terminal and I'm connecting to a Centos 7.

The grep command has a "--color" option. If you have "grep" aliased to "grep --color=auto", then the matched characters will be colored when the output is going directly to a terminal. Using "--color=always" includes the color escape sequences even when the output is going to a file or is piped to another program. "--color=never" does what it implies, and is usually the default.

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OIC

I am just in a normal everyday terminal. SO then this begs the question. If said person uses this type of code. He still got a see what they results are to be sure if he (or she) wrote it correctly. So getting an output that is the same as the input without anything to tell if it pick out the culprit one was looking for. It like putting identical twins in a line up wearing exactly the same thing, then having someone try to pick the one that did it.

I must be needing --color=always then, as I know ls --color=auto is set.

so just do an alias for grep and set it to always, hum.. Now I got a go fiddle with that.
thanks

MOD:

Oh hell yeah! it worked. CCOOOOLL double thanks.

I strongly suggest that you do not set "--color=always" in an alias for "grep". That's going to cause gross problems if you try to use grep in a pipeline and forget that there are going to be ANSI escape sequences in the output. Using "--color=auto", like you probably have in your ls alias, should be fine.