vi, find line and output/output to separate file

I'm looking for a command in VI/VIM to search for particular text in the file and grab the whole line and output in either on the screen or separate file. e.g.开发者_Go百科

This is some line with this _word_ and some other text.
This is some line with this some other text and some other text.

so this would output only the first line..

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:redir > output.txt
:g/_word_/p
:redir END

The line will be output to the screen and to output.txt. See :h :redir.

EDIT: I agree with others who suggest using plain old *nix grep if you can. Situations where you might not be able to use grep:

• You're searching buffer text that doesn't exist in a file on the filesystem.
• You're using Vim-specific regex extensions, like cursor location, column number, marks, etc.
• You want do this in a cross-platform way, and grep might not exist on the system you're using.

redir can be useful in these situations.

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use the g (global) command:

:g/_word_/y

will yank all lines containing _word_

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having mentioned the DOS find command, you probably want to use grep:

grep -h '_word_' * > results

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in vi, from command mode

search for _word_

 /_word_

yank the line

yy

paste the line

p