Merge rust-bitcoin/rust-secp256k1#697: ci: shellcheck checks

ae0a304c2d ci: add shellcheck job (Jose Storopoli)
9f9bd34365 shellcheck: fix warnings (Jose Storopoli)

Pull request description:

  Following https://github.com/rust-bitcoin/rust-bitcoin/pull/2762,
  adding CI shellcheck cheks here as well.

  I also did all fixes that I could find with

  ```bash
  shellcheck **/*.sh
  ```

  If I've missed any please let me know.

ACKs for top commit:
  Kixunil:
    ACK ae0a304c2d
  tcharding:
    ACK ae0a304c2d
  apoelstra:
    ACK ae0a304c2d successfully ran local tests

Tree-SHA512: 0293027439cc922ad9b1ccd5184b481d33fe80b4cd270f425805e7c31108b0bfd7ebe8a76b6aca55300584846f4ca9fbd810faa9ab1d5402e5f1be2bf12fed1a

.github/workflows/shellcheck.yml

@@ -0,0 +1,19 @@
+name: Shellcheck
+on:
+  pull_request:
+    branches:
+      - master
+jobs:
+  shellcheck:
+    name: Shellcheck
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Run ShellCheck
+      uses: ludeeus/action-shellcheck@2.0.0
+      env:
+        SHELLCHECK_OPTS: -x # allow outside sources
+      with:
+        # This code comes directly from upstream libsecp256k1
+        # and should not be linted here.
+        ignore_paths: ./secp256k1-sys/depend/**/*.sh

contrib/extra_tests.sh

@@ -42,10 +42,6 @@ say() {
     echo "extra_tests: $1"
 }
 
-say_err() {
-    say "$1" >&2
-}
-
 verbose_say() {
     if [ "$flag_verbose" = true ]; then
 	say "$1"

contrib/sanitizer.sh

@@ -48,10 +48,6 @@ say() {
     echo "extra_tests: $1"
 }
 
-say_err() {
-    say "$1" >&2
-}
-
 verbose_say() {
     if [ "$flag_verbose" = true ]; then
 	say "$1"

githooks/pre-commit

@@ -26,8 +26,8 @@ if [ "$allownonascii" != "true" ] &&
 	# Note that the use of brackets around a tr range is ok here, (it's
 	# even required, for portability to Solaris 10's /usr/bin/tr), since
 	# the square bracket bytes happen to fall in the designated range.
-	test $(git diff --cached --name-only --diff-filter=A -z $against |
-	  LC_ALL=C tr -d '[ -~]\0' | wc -c) != 0
+	test "$(git diff --cached --name-only --diff-filter=A -z "$against" |
+	  LC_ALL=C tr -d '[ -~]\0' | wc -c)" != 0
 then
 	cat <<\EOF
 Error: Attempt to add a non-ASCII file name.
@@ -44,7 +44,7 @@ EOF
 fi
 
 # If there are whitespace errors, print the offending file names and fail.
-git diff-index --check --cached $against -- || exit 1
+git diff-index --check --cached "$against" -- || exit 1
 
 # Check that code lints cleanly.
 cargo clippy --features=rand,std,recovery,lowmemory,global-context --all-targets -- -D warnings || exit 1