echo "The fox jumped over 3 fences" | grep '[0-9]'
The fox jumped over 3 fences

But , using the regex \d produce a different result

echo "The fox jumped over 3 fences" | grep '\d'
The fox jumped over 3 fences

Why do these types of regex \d \w \s \w do not work with grep or am I using it wrong. Does sed and awk understand those regex types above? Thank you in advance!

There are several variations in regex - regex ain't regex.

-E gets you extended regex, -P gets you PCRE.

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?????

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Dave Morris has done some podcasts about awk and sed at Hacker Public Radio; the shownotes are extremely detailed. They might be a help, as regex is integral to expertise in sed and awk.

(If I ever understand regex, I will feel entitled to call myself a "Linux geek" instead of a "Linux guy.")

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I believe syg00 is telling you to use grep with the -P option for grep to understand perl's short hand regular expressions.

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I have one more problem.

How to suppress the extra white space?

would be nice to show us what is the expected result and/or more examples. And how do you want to solve it (with perl/sed/awk/bash or ???)

I want it to look like this abc 123 using bash

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yes it works! Thanks you pan64!

I thought you had to use quotes if a variable had spaces.

Having just gone over them, these remind me of the shorthand regexs that python uses

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I didn't know the exact name they were called. So I called it regex types. Tobyv did mentioned above it was called short hand regex.

Can sed and awk understand shorthand regex?

glad to help you
if you really want to say thanks just click on yes
And this is the case when you do not need (but in general yes, you have to use quotes).
grep knows 3 different kind of regex, sed knows at least 2, awk has its own style, but more or less similar....
perl has its own PCRE and python knows that too.

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syg00 mentioned them above in #2 and #4. They are perl regular expressions, ported to other languages this is often called perl-compatible regular expression (PCRE). Within perl they are properly called metasymbols and they stand in for some functionality as well as pattern data. You'll find PCRE nearly everywhere these days.

But as to whether sed and awk can understand perl's regular expression metasymbols, the answer is, "no" at least for existing versions to-date.

If you find them useful, then you can get a lot out of one-liners in perl. See the options -e, -i, -n, and -p in
Anything you can do with sed and awk you can do, plus more, in perl.

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