How to use a regular expression to remove lines without a word?

I am using textmate to edit a file. I would like to remove all the lines not containing a word. Here is an example.

apple ipad
hp touch pad
samsung galaxy tab
motorola xoom

How can i remove all the line not containing the word "pad", and get this re开发者_运维百科sult, using Regular Expression??

apple ipad
hp touch pad

Thanks all.

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Replace ^(?!.*pad.*).+$ with empty string

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I'm not sure about doing this kind of thing using regular expressions but you could easily use grep to do this.

For example, if the file textfile contains this:

apple ipad
hp touch pad
samsung galaxy tab
motorola xoom

Open Terminal, and run this command:

grep pad textfile

It'll output this:

apple ipad
hp touch pad

If you want to save the output to a file you can do something like this:

grep pad textfile > filteredfile

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This expression will select lines that contain the word pad: ^.*pad.*$

The ^ character indicates the start of a line, the $ character indicates the end, and .* allows for any number of characters surrounding the word.

This may be too wide-ranged for your purpose in its current state - more specific information is needed.