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

Question

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 result, using Regular Expression??

apple ipad
hp touch pad

Thanks all.

Mesquite

Do you want to remove or keep all lines with the word "pad"? Does "pad" have to be at the end of the line, or anywhere? – Inheritance

"pad" is in anywhere. i want to keep the line with "pad", and remove all the other lines. Kizu's answer solved my problem. Thanks for your help RoToRa. :) – Mesquite

Wow. Thanks for that. It just helped a bunch. – Psychologist

Answer 1

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

Perspire

Would you please explain about this regex? @Perspire – Followup

@Followup (?!) is a “negative lookahead” which is zero-width by itself, but matches only when it won't find the content inside of it. So there we're looking for just anything inside a line — .+, then looking if it doesn't contain pad prefixed with any other symbols — (?!.*pad.*), and if this expression would be found, we can replace it with an empty string that would basically remove the line. – Perspire

I tweaked it a little and used ^(?!.*(10039|10038|10037|10036).*).+$\n to replace lines that don't have any of the words I want and also remove the line break in the process. – Akvavit

Answer 2

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

Fantasia

Thanks daxnitro. This is a good solution. But kizu's answer is better as I can get the result right inside textmate. But thanks so much for your help. :) – Mesquite

Answer 3

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.

Provoke

Yup. This can get all the lines with "pad". But I want to remove the lines without this word. I didn't know how to do that before. Thanks for answer. :) – Mesquite

Thank you for providing an explanation of characters in the expression. – Lawry