cmd: test: add bug-compatibility special case for 'test -n'

It turns out that there is lots of code in the wild, including in the
U-Boot tree itself, which used to rely on

  test -n $somevar

to yield false when $somevar is not defined or empty. See for example
all the occurrences of 'test -n $fdtfile'. That was really only a
quirk of the implementation that refused calls with argc < 3, and not
because it was interpreted as

  test -n "$somevar"

which is how this should be spelled.

While not exactly conforming to POSIX, we can accomodate such scripts
by special-casing a single argument "-n" to be interpreted as if it
comes from code as above with empty $somevar.

Since we only just added the ability to test a string for emptiness
using the single-argument form, it is very unlikely that there is code
doing

  test "$str"

which would now fail if $str happens to be exactly "-n"; such a test
should really always be spelled

  test -n "$str"

Fixes: 8b0619579b2 ("cmd: test: fix handling of single-argument form of test")
Reported-by: Franz Schnyder <franz.schnyder@toradex.com>
Signed-off-by: Rasmus Villemoes <ravi@prevas.dk>
Reviewed-by: Simon Glass <sjg@chromium.org>

diff --git a/cmd/test.c b/cmd/test.c
index 0d0f090386cef58989137a9ecdc39422db897b08..c76ebf800eec7e5a52c9d9476d1ef881f68625ec 100644 (file)
--- a/cmd/test.c
+++ b/cmd/test.c
@@ -75,12 +75,25 @@ static int do_test(struct cmd_tbl *cmdtp, int flag, int argc,
         * Per POSIX, 'test' with 0 arguments should return 1, while
         * 'test <arg>' should be equivalent to 'test -n <arg>',
         * i.e. true if and only if <arg> is not empty.
+        *
+        * However, due to previous versions of U-Boot unconditionally
+        * returning false when 'test' was given less than two
+        * arguments, there are existing scripts that do
+        *
+        *   test -n $somevar
+        *
+        * (i.e. without properly quoting $somevar) and expecting that
+        * to return false when $somevar expands to nothing. It is
+        * quite unlikely that anyone would use the single-argument
+        * form to test a string for being empty and a possible
+        * non-empty value for that string to be exactly "-n". So we
+        * interpret 'test -n' as if it was 'test -n ""'.
         */
        if (argc < 2)
                return 1;
 
        if (argc == 2)
-               return !strcmp(argv[1], "");
+               return !strcmp(argv[1], "") || !strcmp(argv[1], "-n");
 
 #ifdef DEBUG
        {

diff --git a/test/hush/if.c b/test/hush/if.c
index 6129e2c530c6fcab34003f780c15a23de3abafc3..6117c37e53c2a0d0a46b2623e90bcd94973b27be 100644 (file)
--- a/test/hush/if.c
+++ b/test/hush/if.c
@@ -41,6 +41,10 @@ static int hush_test_if_base(struct unit_test_state *uts)
        sprintf(if_formatted, if_format, "test 'abc'");
        ut_assertok(run_command(if_formatted, 0));
 
+       /* Special case: 'test -n' interpreted as 'test -n ""'. */
+       sprintf(if_formatted, if_format, "test '-n'");
+       ut_asserteq(1, run_command(if_formatted, 0));
+
        return 0;
 }
 HUSH_TEST(hush_test_if_base, 0);
@@ -385,6 +389,10 @@ static int hush_test_lbracket_alias(struct unit_test_state *uts)
        ut_asserteq(1, run_command(if_formatted, 0));
        ut_assert_nextline(missing_rbracket_error);
 
+       /* Special case: '[ -n ]' interpreted as '[ -n "" ]'. */
+       sprintf(if_formatted, if_format, "[ -n ]");
+       ut_asserteq(1, run_command(if_formatted, 0));
+
        return 0;
 }
 HUSH_TEST(hush_test_lbracket_alias, UTF_CONSOLE);