Add file support

[bep]

Useful little util.

It would be nice if it, in addition to the stdin support, could work with file(s) as arguments.

Currently this works:

cat myfile.txt | xurls

This just hangs there, waiting:

xurls myfile.txt

An example of a Go tool that works as expected for a *nix CLI tool would be ccat.

[mvdan]

Is it a common pattern for all unix tools that work with stdin/stdout to also accept files as arguments? I don't see why it shouldn't be supported, but just wondering.

I'm also thinking about multiple files. I'm guessing you would have xurls file1 file2 work just like cat file1 file2 | xurls, as in without distinguishing files?

[mvdan]

Also, of course the tool hanging when given an argument is a bug :)

[bep]

Most (all?) of the *nix tools in the GNU Utils package that works on text works on files + stdin, cat, grep, more, less, tail ... So it's common. So common it was the first my fingers tried.

Ideally it should work like cat does, so xurls file1 file2 xurls *.txt etc should work (maybe spin up some Go routines to make it snappier).

[mvdan]

Done. I've followed the pattern that cat uses, explained in the commit for future reference.

[mvdan]

I just noticed your mentioning of goroutines. For multiple files it could be used. They are cheap so that shouldn't be a problem, and it could indeed speed things up for large files or async I/O.

The only disadvantage I can think of is that the urls will no longer be output in the correct order like cat prints the lines in order, even though at no point we say we're doing them in order.

[bep]

The go routines would be a nice addon (not important), but is a different issue.

[mvdan]

Could you please open a separate issue describing it?