unexpand: add -f short alias for --first-only (#8229)

Author: GTimothy

docs/src/extensions.md

@@ -193,3 +193,8 @@ Just like on macOS, `base32/base64/basenc` provides `-D` to decode data.
 ## `shred`
 
 The number of random passes is deterministic in both GNU and uutils. However, uutils `shred` computes the number of random passes in a simplified way, specifically `max(3, x / 10)`, which is very close but not identical to the number of random passes that GNU would do. This also satisfies an expectation that reasonable users might have, namely that the number of random passes increases monotonically with the number of passes overall; GNU `shred` violates this assumption.
+
+## `unexpand`
+
+GNU `unexpand` provides `--first-only` to convert only leading sequences of blanks. We support a
+second way: `-f` like busybox.

src/uu/unexpand/src/unexpand.rs

@@ -175,6 +175,7 @@ pub fn uu_app() -> Command {
         )
         .arg(
             Arg::new(options::FIRST_ONLY)
+                .short('f')
                 .long(options::FIRST_ONLY)
                 .help(get_message("unexpand-help-first-only"))
                 .action(ArgAction::SetTrue),

tests/by-util/test_unexpand.rs

@@ -95,6 +95,24 @@ fn unexpand_first_only_1() {
         .stdout_is("\t\t  A     B");
 }
 
+#[test]
+fn unexpand_first_only_2() {
+    new_ucmd!()
+        .args(&["-t3", "-f"])
+        .pipe_in("        A     B")
+        .succeeds()
+        .stdout_is("\t\t  A     B");
+}
+
+#[test]
+fn unexpand_first_only_3() {
+    new_ucmd!()
+        .args(&["-f", "-t8"])
+        .pipe_in("        A     B")
+        .succeeds()
+        .stdout_is("\tA     B");
+}
+
 #[test]
 fn unexpand_trailing_space_0() {
     // evil