Shellcheck rewrites (#9597)

* Fix SC2001: See if you can use ${variable//search/replace} instead.

* Fix SC2010: Don't use ls | grep. Use a glob or a for loop with a condition to allow non-alphanumeric filenames.

* Fix SC2012: Use find instead of ls to better handle non-alphanumeric filenames.

* Fix SC2015: Note that A && B || C is not if-then-else. C may run when A is true.

* Fix SC2028: echo may not expand escape sequences. Use printf.

* Fix SC2034: variable appears unused. Verify use (or export if used externally).

* Fix SC2035: Use ./*glob* or -- *glob* so names with dashes won't become options.

* Fix SC2071: > is for string comparisons. Use -gt instead.

* Fix SC2154: variable is referenced but not assigned

* Fix SC2164: Use 'cd ... || exit' or 'cd ... || return' in case cd fails.

* Fix SC2188: This redirection doesn't have a command. Move to its command (or use 'true' as no-op).

* Fix SC2236: Use -n instead of ! -z.

* Fix SC2242: Can only exit with status 0-255. Other data should be written to stdout/stderr.

* Fix SC2086: Double quote to prevent globbing and word splitting.

Co-authored-by: Mehrdad <noreply@github.com>

doc/dev/bin/pip_download_test.sh

@@ -32,11 +32,13 @@ do
     env_name="${RAY_VERSION}-${PYTHON_VERSION}-env"
     conda create -y -n "${env_name}" python=${PYTHON_VERSION}
     conda activate "${env_name}"
-    echo "\n\n\n========================================================="
+    printf "\n\n\n"
+    echo "========================================================="
     echo "Python version."
     python --version
     echo "This should be equal to ${PYTHON_VERSION}"
-    echo "=========================================================\n\n\n"
+    echo "========================================================="
+    printf "\n\n\n"
 
     pip install redis==3.3.2
     pip install msgpack==0.6.2
@@ -45,13 +47,15 @@ do
     pip install --index-url https://test.pypi.org/simple/ ray
 
     failed=false
-    echo "\n\n\n========================================================="
+    printf "\n\n\n"
+    echo "========================================================="
     if python sanity_check.py; then
         echo "PYTHON ${PYTHON_VERSION} succeed sanity check."
     else
         failed=true
     fi
-    echo "=========================================================\n\n\n"
+    echo "========================================================="
+    printf "\n\n\n"
 
     conda deactivate
     conda remove -y --name "${env_name}" --all