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# UNIX text filters, part 2.5 of 3: expand and unexpand
*This post is part of a [series](../../series)*
Last week some guys at my company gave a little lecture on
[rust](https://www.rust-lang.org). They gave us some practical exercises,
with some partially-written source files to complete. Unfortunately, the
source files used spaces instead of TABs!
Luckily I knew how to use `unexpand` to fix this. And in case you
are shaking your head in horror because you prefer spaces, worry
not: `expand` can save you when you face the opposite problem.
## expand
The `expand` command converts tabs into spaces. By default every
TAB character *at the beginning of each line* is replaced by 8
spaces, but you can choose a different width with the `-t` option.
You can also choose to expand *all* TABs, not just the leading ones,
using the `-a` option. For example:
```
$ echo ' hello world?' | expand -t 3
hello world?
```
As you can see, the TAB in the middle of the line is preserved.
Well I guess you can't really see it. Also, I am pretty sure the
markdown-to-html converter I use turns tabs into spaces anyway.
This example is a trainwreck, let's move on.
## unexpand
Unsurprisingly, `unexpand` does just the opposite of `expand`: it
converts groups of leading spaces into TABs. So the command I used
to "fix" the source files for the rust exercises was:
```
$ unexpand -t 4 main.rs
```
or to be more precise, since I wanted to replace the original file:
```
$ unexpand -t 4 main.rs > main.rs.2 && mv main.rs.2 main.rs
```
or to be even more precise, since I wanted to do this for multiple files:
```
$ for f in *.rs; do unexpand $f > $f.2 && mv $f.2 $f; done
```
## Quirks
For some reason, the OpenBSD version of `unexpand` does not allow
using the `-t` option. So if I had brought my OpenBSD laptop at the
rust lecture I would have been stuck with spaces :(
*Next in the series: [fold](../2024-05-31-fold)*
|
