Question

How can I reset the “pointer” of a file to its start without reopening it? (Something like fseek in C?)

For example, I have a file that I want to grep for two patterns:

f=open('test') => #<File:test> 
f.grep(/llo/)  => ["Hello world\n"] 
f.grep(/wo/)   => [] 

Is it possible to reset f without reopening the file?

Note: I am not looking for workarounds; I can think some on my own ;).

Answer 1

Use rewind

Positions ios to the beginning of input, resetting lineno to zero.

f = File.new("testfile") 
f.readline   #=> "This is line one\n"
f.rewind     #=> 0 
f.lineno     #=> 0 
f.readline   #=> "This is line one\n"