tests: use more POSIX shell features our test scripts

Since commit 'v1.12-36-g2d68fd9' of 2012-05-07, "configure: search a
sturdy POSIX shell to be used in the testsuite", the shell running
our test script is assured to be a POSIX-conforming shell, so we can
use the more modern and flexible idioms and features that we couldn't
use when we also aimed at compatibility with non-POSIX Bourne shells,
like Solaris /bin/sh.

* t/README: Suggest to use POSIX shell features liberally in test cases,
with possible exception of Makefile recipes and configure shell code.
* Several tests: Adjust to use more POSIX shell features; e.g., $(...)
rather than `...`, $((...)) rather than `expr ...`, "if ! CMD; then ..."
instead of "if CMD; then :; else ...", and so on.
In several places, when using the 'test' built-in, prefer '-eq' over
'=' for numeric comparisons, and prefer "grep -c PATTERN FILE" over
"grep PATTERN FILE | wc -l".
Throw in other low-hanging easy improvements and fixlets while we are
at it.
* t/ax/depcomp.sh, t/ax/tap-summary-aux.sh, t/ax/tap-functions.sh,
defs, defs-static.in: Likewise.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/t/README b/t/README
index 5f967d271..57cab89d4 100644
--- a/t/README
+++ b/t/README
@@ -278,6 +278,22 @@ Do
 Do not
 ------
 
+  In test scripts, prefer using POSIX constructs over their old
+  Bourne-only equivalents:
+
+    - use $(...), not `...`, for command substitution;
+    - use $((...), not `expr ...`, for arithmetic processing;
+    - liberally use '!' to invert the exit status of a command, e.g.,
+      in idioms like "if ! CMD; then ...", instead of relying on clumsy
+      paraphrases like "if CMD; then :; else ...".
+    - prefer use of ${param%pattern} and ${param#pattern} parameter
+      expansions over processing by 'sed' or 'expr'.
+  
+  Note however that, when writing Makefile recipes or shell code in a
+  configure.ac, you should still use `...` instead, because the Autoconf
+  generated configure scripts do not ensure they will find a truly POSIX
+  shell (even though they will prefer and use it *if* it's found).
+
   Do not test an Automake error with "$AUTOMAKE && Exit 1", or in three
   years we'll discover that this test failed for some other bogus reason.
   This happened many times.  Better use something like