commit d1504905f459494c99bccb3be17f6f70258e1e0c
parent 57056f658bbba0ea1b3dd9fece8dc00c17e2dade
Author: Sebastiano Tronto <sebastiano@tronto.net>
Date: Sun, 7 Apr 2024 07:01:58 +0200
added blog post
Diffstat:
3 files changed, 61 insertions(+), 0 deletions(-)
diff --git a/src/blog/2024-03-28-cut/cut.md b/src/blog/2024-03-28-cut/cut.md
@@ -136,3 +136,5 @@ something more complicated with the data than just printing it out.
For this reason I have always relied on more complete languages,
like C or Python, rather than shell scripting. But `cut` is definitely
a convenient tool to be familiar with, given how simple it is!
+
+*Next in the series: [expand and unexpand](../2024-04-07-expand-unexpand)*
diff --git a/src/blog/2024-04-07-expand-unexpand/expand-unexpand.md b/src/blog/2024-04-07-expand-unexpand/expand-unexpand.md
@@ -0,0 +1,58 @@
+# UNIX text filters, part 2.5 of 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 si 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 :(
diff --git a/src/series/series.md b/src/series/series.md
@@ -33,6 +33,7 @@ of complexity: `grep`, `sed` and `awk`. Work in progress.
* Part 2.2: [head and tail](../blog/2024-02-20-head-and-tail)
* Part 2.3: [rev](../blog/2024-03-27-rev)
* Part 2.4: [cut](../blog/2024-03-28-cut)
+* Part 2.5: [expand and unexpand](../blog/2024-04-07-expand-unexpand)
* Part 3: awk (coming "soon")
## The UNIX shell as an IDE
