Minor script cleanup

quickrun

-#!/bin/bash
+#!/usr/bin/env bash
 # quickrun runs ShellCheck in an interpreted mode.
 # This allows testing changes without recompiling.
 

quicktest

-#!/bin/bash
+#!/usr/bin/env bash
 # quicktest runs the ShellCheck unit tests in an interpreted mode.
 # This allows running tests without compiling, which can be faster.
 # 'cabal test' remains the source of truth.

striptests

@@ -5,6 +5,7 @@
 set -o pipefail
 
 sponge() {
+  local data
   data="$(cat)"
   printf '%s\n' "$data" > "$1"
 }
@@ -22,7 +23,7 @@ modify() {
 }
 
 detestify() {
-  echo "-- AUTOGENERATED from ShellCheck by striptests. Do not modify."
+  printf '%s\n' '-- AUTOGENERATED from ShellCheck by striptests. Do not modify.'
   awk '
     BEGIN {
       state = 0;
@@ -52,7 +53,7 @@ detestify() {
 
 
 
-if [[ ! -e ShellCheck.cabal ]]
+if [[ ! -e 'ShellCheck.cabal' ]]
 then
   echo "Run me from the ShellCheck directory." >&2
   exit 1
@@ -64,7 +65,7 @@ then
   exit 2
 fi
 
-modify ShellCheck.cabal sed -e '
+modify 'ShellCheck.cabal' sed -e '
   /QuickCheck/d
   /^test-suite/{ s/.*//; q; }
   '