git-branch-list: Verify ID is an integer before doing `checkout`

When running:

    $ git branch-list 2

we want to ensure the argument "2" in the example above is an integer.
If so, we take it to represent a branch-list ID. Otherwise an error code
should be returned.

Thanks to Peter Ho on StackOverflow for the neat Bash integer test:
https://stackoverflow.com/questions/2210349/bash-test-whether-string-is-valid-as-an-integer/19116862#19116862

1 files changed, 7 insertions, 2 deletions

diff --git a/git-branch-list b/git-branch-list
index bd85160..bf55624 100755
--- a/git-branch-list
+++ b/git-branch-list
@@ -93,7 +93,12 @@ case "$command" in
 		exit $?
 		;;
 	*)
-		# if $1 is an integer
-		checkout_branch "$1"
+		# If `$1` is an integer
+		if [ "$1" -eq "$1" ] 2>/dev/null; then
+			checkout_branch "$1"
+		else
+			exit 1
+		fi
+
 		;;
 esac