Make seed-gitignore more robust and only update the ignore if needed

diff --git a/vcsh b/vcsh
index dd05f0ead3cc5aaff22318a9c962a7d9525a6caf..f4d98ad9c0c0a8c97bdd3a8fc9bd4d4143e53716 100755 (executable)
--- a/vcsh
+++ b/vcsh
@@ -193,14 +193,24 @@ elif [ "$1" = 'seed-gitignore' ]; then
                        file="$new"
                done;
        done | sort -u | sed 's/^/!/')
-       [ -e "$HOME/.gitignore.d/$2" ] &&
-       echo "$SELF: info: $HOME/.gitignore.d/$2 exists, moving it to $HOME/.gitignore.d/$2.bak" &&
-       mv -f "$HOME/.gitignore.d/$2" "$HOME/.gitignore.d/$2.bak"
-       echo '*' > "$HOME/.gitignore.d/$2"
+       tempfile=$(mktemp) ||
+               (echo "$SELF: fatal: could not create tempfile" && exit 1) 
+       echo '*' > "$tempfile"
        for gitignore in $gitignores; do
-               echo "$gitignore" >> "$HOME/.gitignore.d/$2"
+               echo "$gitignore" >> "$tempfile"
        done
+       diff -N "$tempfile" "$HOME/.gitignore.d/$2" > /dev/null &&
+               rm -f "$tempfile" &&
+               return
+       if [ -e "$HOME/.gitignore.d/$2" ]; then
+               echo "$SELF: info: $HOME/.gitignore.d/$2 differs from new data, moving it to $HOME/.gitignore.d/$2.bak"
+               mv -f "$HOME/.gitignore.d/$2" "$HOME/.gitignore.d/$2.bak" ||
+                       (echo "$SELF: fatal: could not move $HOME/.gitignore.d/$2 to $HOME/.gitignore.d/$2.bak" && exit 1)
+       fi
+       mv -f "$tempfile" "$HOME/.gitignore.d/$2" ||
+               (echo "$SELF: fatal: could not move $tempfile to $HOME/.gitignore.d/$2" && exit 1)
        cd "$old_dir"
+       verbose "seed-gitignore end"
 
 else
        verbose "defaulting to calling help()"