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I have a very large text file (~5g)

Is this a single 5GB file used over and over? Or a new 5GB file each time?

I need to search each time

How many searches do you need to do? How often? What is your target time.

I want to search for 'text2' and retrieve 2 and 3,

How long are the texts? Are they ascii or unicode?

but the sorting process takes ages

How long is "ages"?

The more clearly you explain your task, the more likely that someone will see a viable solution.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

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