tests: avoid side effects of $SHELL environment variable

Since non interactive shells don't generally set $SHELL,
its value is propagated through the tests and may cause issues;
for example if $SHELL implicitly adjusts $PATH when run.
Instead we set $SHELL to that determined by the posix-shell module,
and use that consistently for all test sub scripts,
including those created thorugh the `split --filter` command.

* tests/local.mk: Explicitly set $SHELL to $(PREFERABLY_POSIX_SHELL)
which defaults to $CONFIG_SHELL and thus usually /bin/sh.
* tests/envvar-check: Remove bash environment variables with
side effects, in case /bin/bash was selected for $SHELL.
* tests/misc/help-version.sh: Remove redundant initialization of $SHELL.
* tests/install/strip-program.sh: Use $SHELL for sub script.
* tests/misc/sort-compress-hang.sh: Likewise.
* tests/misc/sort-compress-proc.sh: Likewise.
* tests/misc/sort-compress.sh: Likewise.
* tests/misc/timeout-group.sh: Likewise.
* tests/rm/fail-eperm.xpl: Remove redundant elision of bash env vars.
* tests/misc/pwd-long.sh: Likewise.

1 files changed, 3 insertions, 2 deletions

diff --git a/tests/misc/sort-compress-proc.sh b/tests/misc/sort-compress-proc.sh
index 4ad42d514..05017a54f 100755
--- a/tests/misc/sort-compress-proc.sh
+++ b/tests/misc/sort-compress-proc.sh
@@ -32,8 +32,9 @@ insize=$(stat -c %s - <in) || fail=1
 # This compressor's behavior is adjustable via environment variables.
 export PRE_COMPRESS=
 export POST_COMPRESS=
-cat <<\EOF >compress || framework_failure_
-#!/bin/sh
+
+printf '%s\n' '#!'"$SHELL" >compress || framework_failure_
+cat <<\EOF >>compress || framework_failure_
 eval "$PRE_COMPRESS"
 tr 41 14 || exit
 eval "$POST_COMPRESS"