expand-unexpand.md (1875B)
1 # UNIX text filters, part 2.5 of 3: expand and unexpand 2 3 *This post is part of a [series](../../series)* 4 5 Last week some guys at my company gave a little lecture on 6 [rust](https://www.rust-lang.org). They gave us some practical exercises, 7 with some partially-written source files to complete. Unfortunately, the 8 source files used spaces instead of TABs! 9 10 Luckily I knew how to use `unexpand` to fix this. And in case you 11 are shaking your head in horror because you prefer spaces, worry 12 not: `expand` can save you when you face the opposite problem. 13 14 ## expand 15 16 The `expand` command converts tabs into spaces. By default every 17 TAB character *at the beginning of each line* is replaced by 8 18 spaces, but you can choose a different width with the `-t` option. 19 You can also choose to expand *all* TABs, not just the leading ones, 20 using the `-a` option. For example: 21 22 ``` 23 $ echo ' hello world?' | expand -t 3 24 hello world? 25 ``` 26 27 As you can see, the TAB in the middle of the line is preserved. 28 Well I guess you can't really see it. Also, I am pretty sure the 29 markdown-to-html converter I use turns tabs into spaces anyway. 30 This example is a trainwreck, let's move on. 31 32 ## unexpand 33 34 Unsurprisingly, `unexpand` does just the opposite of `expand`: it 35 converts groups of leading spaces into TABs. So the command I used 36 to "fix" the source files for the rust exercises was: 37 38 ``` 39 $ unexpand -t 4 main.rs 40 ``` 41 42 or to be more precise, since I wanted to replace the original file: 43 44 ``` 45 $ unexpand -t 4 main.rs > main.rs.2 && mv main.rs.2 main.rs 46 ``` 47 48 or to be even more precise, since I wanted to do this for multiple files: 49 50 ``` 51 $ for f in *.rs; do unexpand $f > $f.2 && mv $f.2 $f; done 52 ``` 53 54 ## Quirks 55 56 For some reason, the OpenBSD version of `unexpand` does not allow 57 using the `-t` option. So if I had brought my OpenBSD laptop at the 58 rust lecture I would have been stuck with spaces :(