support updating previously corrected folder names

bin/dasht-docsets-extract

@@ -30,6 +30,8 @@
 # location specified by the `DASHT_DOCSETS_DIR` environment variable and then
 # renames their extracted directories to match their rootnames (sans `.tgz`).
 #
+# If an extracted directory already exists, its contents are updated in place.
+#
 # ## ENVIRONMENT
 #
 # `DASHT_DOCSETS_DIR`
@@ -52,10 +54,18 @@
 
 test $# -gt 0
 for tgz; do
-  tar -v -C "$DASHT_DOCSETS_DIR" -z -x -f "$tgz" # extract archive
+  want="$DASHT_DOCSETS_DIR/$(basename "$tgz" .tgz).docset"
+  have="$DASHT_DOCSETS_DIR/$(tar -z -t -f "$tgz" | head -1 | sed 's,/.*,,')"
+
+  # for dasht-docsets-update(1), the extracted directory will already exist
+  # with the correct name, but we need to temporarily rename it back to the
+  # wrong name so that the archive extraction below can update its contents
+  # in place, rather than extracting out to a new (and different) directory
+  test "$have" = "$want" || test -d "$want" && mv "$want" "$have"
+
+  # extract the archive; the extracted directory's path is defined by $have
+  tar -v -C "$DASHT_DOCSETS_DIR" -z -x -f "$tgz"
 
-  # ensure that extracted directory has same rootname as archive
-  actual="$DASHT_DOCSETS_DIR/$(tar -z -t -f "$tgz" | head -1 | sed 's,/.*,,')"
-  wanted="$DASHT_DOCSETS_DIR/$(basename "$tgz" .tgz).docset"
-  test "$actual" = "$wanted" || mv "$actual" "$wanted"
+  # rename the extracted directory to have the same rootname as the archive
+  test "$have" = "$want" || mv "$have" "$want"
 done

man/man1/dasht-docsets-extract.1

@@ -23,6 +23,8 @@ located in a subdirectory one level above the current working directory.
 Extracts the given Dash \[la]https://kapeli.com/dash\[ra] docset archive \fIFILE\fPs (\fB\fC*.tgz\fR files) into the
 location specified by the \fB\fCDASHT_DOCSETS_DIR\fR environment variable and then
 renames their extracted directories to match their rootnames (sans \fB\fC\&.tgz\fR).
+.PP
+If an extracted directory already exists, its contents are updated in place.
 .SH ENVIRONMENT
 .TP
 \fB\fCDASHT_DOCSETS_DIR\fR