Extracting certain lines from a large text file

[Feek]

I have a collection of very large csv files and I want to try and extract every line which contains a certain string.

The files are on average around 500Mb each and contain more lines than any application I've got can handle so I'm sure this will be some command line work using something like sed or cat but I'm not sure what to use.

Can anyone help please?

Thanks.

 

[On Holiday]

 

[Feek]

Of course! I was getting too complicated.

grep 'text' /filename > output.txt

Done in ten seconds!