Scripts and tools & Docs: Used #!/usr/bin/env bash instead of obsolete #!/bin/bash, added linting for .sh files shebang and updated the Developer Notes.

contrib/qos/tc.sh

@@ -1,3 +1,5 @@
+#!/usr/bin/env bash
+#
 # Copyright (c) 2017 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or https://www.opensource.org/licenses/mit-license.php .

doc/developer-notes.md

@@ -276,6 +276,31 @@ Strings and formatting
     `wcstoll`, `wcstombs`, `wcstoul`, `wcstoull`, `wcstoumax`, `wcswidth`,
     `wcsxfrm`, `wctob`, `wctomb`, `wctrans`, `wctype`, `wcwidth`, `wprintf`
 
+Scripts
+--------------------------
+
+### Shebang
+
+- Use `#!/usr/bin/env bash` instead of obsolete `#!/bin/bash`.
+
+  - [*Rationale*](https://github.com/dylanaraps/pure-bash-bible#shebang):
+
+    `#!/bin/bash` assumes it is always installed to /bin/ which can cause issues;
+
+    `#!/usr/bin/env bash` searches the user's PATH to find the bash binary.
+
+  OK:
+
+```bash
+#!/usr/bin/env bash
+```
+
+  Wrong:
+
+```bash
+#!/bin/bash
+```
+
 Source code organization
 --------------------------
 

test/lint/lint-shebang.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# Shebang must use python3 (not python or python2)
+# Assert expected shebang lines
 
 export LC_ALL=C
 EXIT_CODE=0
@@ -10,4 +10,11 @@ for PYTHON_FILE in $(git ls-files -- "*.py"); do
         EXIT_CODE=1
     fi
 done
+for SHELL_FILE in $(git ls-files -- "*.sh"); do
+    if [[ $(head -n 1 "${SHELL_FILE}") != "#!/usr/bin/env bash" &&
+          $(head -n 1 "${SHELL_FILE}") != "#!/bin/sh" ]]; then
+        echo "Missing expected shebang \"#!/usr/bin/env bash\" or \"#!/bin/sh\" in ${SHELL_FILE}"
+        EXIT_CODE=1
+    fi
+done
 exit ${EXIT_CODE}