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How to delete words using pattern in vi

Posted on 2010-11-19
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Last Modified: 2012-06-27
Hi,

I am trying to find all words in my file that are 4 characters long and start with a B or b and delete those words. I am trying to break down the regular expression into parts and build onto it as I get things working. So far, I am just trying to delete words starting with a B using this vi command: g/^B/dw, but I get a 'Not an editor command: dw' error. Could someone point me in the right direction? thanks.
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Question by:grnmachine
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7 Comments
 
LVL 9

Expert Comment

by:expert_tanmay
ID: 34176748
you have to use
:s/\<[Bb]\p\+//g
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Hatrix76 earned 500 total points
ID: 34177036
What you are trying to do does not work with the range command.

The range command is for lines, if you do :g/^B/d then it deletes all lines beginning with B, if you do :g/Beg/d than all lines which contain Beg somewhere will be deleted.

With this command you can not delete words. Words only is best to delete with a search and replace command:

:s/[Bb].\{3\}//g

will do what you want, find words which starts with an B or b, and are exactly 4 characters long ( "." = any character and \{3\} means the entity before ( "." = any character) exactly 3 times, e.g. 6\{3\} matches 666), and replace them with nothing (s/<searchpattern>/<replacestring/g) the last g is a flag which means continue replacing after you find the first replacement on a line.

Standard regular expressions do not need the escaping for {} ... this is a bit difficult, perl regex, vi and sed, awk, grep have all different semantics regarding escaping ... so you'l have to read their respective manuals :-)

best


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Author Comment

by:grnmachine
ID: 34177082
The command just seems to highlight the whole line that has four letter words starting with a B or b. I would like to have the command find four letter words and delete only those words starting with a B or b. I'm I entering the command incorrectly? Could you break down what each item in the expression means? I am just learning vi/regular expressions and its still a bit confusing. Thanks.
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LVL 9

Assisted Solution

by:expert_tanmay
expert_tanmay earned 500 total points
ID: 34177084
Oh yes I missed out 4 characters long you have to use the following

:s/\<[Bb]\p\{3\}//g
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Author Comment

by:grnmachine
ID: 34177087
@Hatrix76

Okay, let me try it out and I will get back to you. Thanks.
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LVL 9

Expert Comment

by:expert_tanmay
ID: 34177148
The alphabet s is for search/substitute
\< means starting of word
[Bb] means B or b
\p means printable characters
\{3\} means as it is followed by \p match 3 printable characters after B or b

// means substitute with nothing.
g means global in other words the entire file.
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LVL 6

Expert Comment

by:mohansahu
ID: 34185901
Hi,

For deleting a particular word in a file,Please use the following command.

:%s/\<mohan\>.\{0}//

Note:here Mohan is the word for delete in the file.

Cheers,
Mohan Sahu
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