mjhjmtu

I have problem understanding /.*/ according to things written in books, this prints the entire line of the text. we know that. means any character, and * means zero or more occurrence of the preceding character. so I expect that /.*/ finds something like rrr qqqq abbbbb, I mean continuouslynuesly repetition of a single character.

but this is not the thing it does. why?

my second question is: why /.+/ doesn't do the same thing?? in the text I'm trying on the result is ?

No, the * in .* means "any number of the preceding expression", i.e. zero or more of whatever character that matches the expression ..

This means that .* will match aaaa as well as abcd since all of the characters in abcd matches .. It will also match an empty line, since it allows for zero matches.

If you'd like to find a line that contains a repeated character, use

/(.)11*/

This expression matches "any character, then the same character, and then any number of more of the same character". The 1* could arguably be removed unless you're looking for lines that contain only a repeated character, in which case you should anchor the expression to the start and end of the line, as in

/^(.)11*$/

The ed editor supports basic regular expressions. The + modifier is an extended regular expression modifier. The ? that you get from ed when using /.+/ would be followed by no match (or No match in GNU ed) if you had enabled error explanations with the H command. This is because it tries to find a line with a + in it, preceded by some other character.

The .+ extended regular expression ("match one or more of any character") is equivalent to the basic regular expression ..*, i.e. "match a character, and then zero or more of any character".

According to its manual, GNU ed should support + in regular expressions, so that ..* is equivalent to .+, but GNU ed 1.14.2 on my OpenBSD system does not do this.