Add First filter #9
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| err := scanner.Err() | ||
| if err != nil { | ||
| p.SetError(err) | ||
| } |
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How does this implementation behave, if you pass a very big file and you use the First() filter? With the unix commands, the pipe is closed by head after 10 lines, which allows all the commands in front of head in the pipe to end as well, without the need of reading the whole file.
Would this work here as well, if we would close the pipe?
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That is a very good point. We don't read any more of the pipe than we need to, but we also don't close it. I'd better add that...
| // First reads from the pipe, and returns a new pipe containing only the first N | ||
| // lines. If there is an error reading the pipe, the pipe's error status is also | ||
| // set. | ||
| func (p *Pipe) First(lines int) *Pipe { |
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Currently negative values are treated the same as 0. head has a special interpretation of negative numbers, which could be added here as well.
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GNU head allows negative arguments for -n option, meaning to print all but the last - argument value counted - lines of each input file
That sounds like effectively it would behave like Last()—well, we don't have that yet, but when we do, we won't need to worry about this :)
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No, it is not like Last(), because it prints everything BUT the last n lines, where Last() prints ONLY the last n lines. So in fact it is more like an inverted Last().
A similar option is available in tail als well.
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Oh yes, I wasn't reading that properly. Well, it's a neat feature, but I don't have a use case for it—so I'll wait until there is one.
See #7 for a discussion and use case.