Don't ignore "null" values in variable expansions

Replace ${var:-default} with ${var-default}.

I learned something new about shell scripting today.  From bash manual:
===
When not performing substring expansion, using the form described
below (e.g., ‘:-’), Bash tests for a parameter that is unset or null.
Omitting the colon results in a test only for a parameter that is
unset. Put another way, if the colon is included, the operator tests
for both parameter’s existence and that its value is not null; if
the colon is omitted, the operator tests only for existence.
===

The immediate problem I need to fix is handling of
host_aarchXX_excludecheck and host_x86_64_excludecheck parameters
in tcwg-buildfarm.sh.  With ":-" syntax the empty ("null") values are
replaced by defaults, causing GCC testsuite to be ignored on aarchXX
hosts when "--host_aarchXX_excludecheck ''" is given.

There happens to be a single usage ":-" in ${rw:-rw} in
start-container-qemu.sh, where ":-" is actually needed.

Change-Id: Ibc8e070b698e1c76e2161eb65d40639b8cdec1f3

1 files changed, 4 insertions, 4 deletions

diff --git a/tcwg-update-host-containers.sh b/tcwg-update-host-containers.sh
index cb121249..33351ed0 100755
--- a/tcwg-update-host-containers.sh
+++ b/tcwg-update-host-containers.sh
@@ -5,10 +5,10 @@ set -ef -o pipefail
 . $(dirname $0)/jenkins-helpers.sh
 convert_args_to_variables "$@"
 
-container="${container:-jenkins}"
-distro="${distro:-xenial}"
-group="${group:-default}"
-verbose="${verbose:-true}"
+container="${container-jenkins}"
+distro="${distro-xenial}"
+group="${group-default}"
+verbose="${verbose-true}"
 
 set -u