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Comment by jlp__inf | Hacker News Reader

Thanks for sharing this, I’m learning a lot from it.

So if I understand correctly, it’s selection-based, right? You first select a region, and then you can apply further selections inside it?

So you kind of build nested selections to match exactly what you want (almost like a conditional tree).

And then you apply operations on the current selection

For example substitution with something like c/PATTERN/, is that correct?

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That's exactly right. A few unmentioned details:

. The dot (".") never matches newlines, which keeps line-oriented idioms from accidentally spanning newlines [1]

. Changes must be sequential and non-overlapping (that's why I deleted the whole thing before processing in the third example).

. Sam matches only the original input, not past changes.

. Addresses (expressions before commands) select a single range, x commands select multiple ranges and loop over it.

[1]: https://p9f.org/sys/doc/sam/sam.html, Regular expressions

Thanks for those complementary informations.

Also, while i'm learning it, maybe that the sam traduction for the first file would be simpler, like:

,x/\n +/ c/ /

Also, i managed to, i think simplify the second example to: 1,$-2 x/./ { a/->/ /./ t . } 1,$-2 { p } q

Which taught me a lot, because at first, i did not understand why we would stop at last line - 2 ($ - 2), but in fact yeah last line is the very last "\n", that is why we stop at $ - 2 to not do E->weird.

I'm starting to truly love sam

and yess, g/PATTERN/ and /v/PATTERN/ are supzr powerful, creating branch conditions based on wether or not they (do not)match a PATTERN.

based on what you wrote:

i just add trailing \n normalization at the end

, x/(.+\n)+|\n+/ { g/./ x/\n/ c/ / v/./ c/\n/ } $ a/\n/ , x/\n+$/ c/\n/ w file_out.txt q

Yeah, sam is not universal, but it can solve complex tasks more simply by just running it a few times. The final example already normalizes \n (v/./ c/\n/) in a single pass, but we can make it even simpler by just writing:

    , x/(.+\n)+/ .,+#0-#1 x/\n/ c/ /
    , x/\n+/ c/\n/

(I haven’t tested it.)

I’m glad that sam worked out for you. You can learn more from [1] and [2]. If you need any help, you’re always welcome to ask me.

[1]: https://ratfactor.com/papers/sam_tut.pdf

[2]: https://9p.io/sources/contrib/steve/other-docs/struct-regex....

thanks, i published an article draft about SAM inspired by your examples (referencing sources / this comment section)

Do not hesitate to pin point improvements.

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