What does this regex mean and why

Posted by Kalec on Ask Ubuntu See other posts from Ask Ubuntu or by Kalec
Published on 2012-06-05T16:17:22Z Indexed on 2012/06/05 16:48 UTC
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regex

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sed

$ sed "s/\(^[a-z,0-9]*\)\(.*\)\( [a-z,0-9]*$\)/\1\2 \1/g" desired_file_name

I apreciate it even if you only explain part of it or at lest structure it with words as in s\alphanumerical_at_start\something\alphanumerical_at_end\something_else\global

Could someone explain what that means, why and are all regEx so ... awful ?

I know that it replaces the first lowcase alphanumerical word with the last one. But could you explain bit by bit what's going on here ? what's with all the /\ and \(.*\)\ and everything else ?

I'm just lost.

EDIT: Here is what I do get: (^[a-z0-9]*) starting with a trough z and 0 trough 9; and [a-z,0-9]*$ is the same but the last word (however [0-9,a-z] = just first 2 characters / first character, or the entire word ?). Also: what does the * or the \(.*\)\ even mean ?

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