Scripts: use POSIX subcommand invocation

scripts/check-pr.sh

@@ -49,7 +49,7 @@ function check_diff {
   local line
   local entry
 
-  git_diff=`git diff --name-status --find-copies-harder --diff-filter=AC --relative=pages/ master`
+  git_diff=$(git diff --name-status --find-copies-harder --diff-filter=AC --relative=pages/ master)
 
   if [ -n "$git_diff" ]; then
     echo -e "Check PR: git diff:\n$git_diff" >&2
@@ -108,7 +108,7 @@ MSG_NOT_DIR='The file `%s` does not look like a directory.\n'
 MSG_NOT_FILE='The file `%s` does not look like a regular file.\n'
 MSG_NOT_MD='The file `%s` does not have a `.md` extension.\n'
 
-PLATFORMS=`ls pages/`
+PLATFORMS=$(ls pages/)
 
 if [ "$TRAVIS" = "true" ] && [ "$TRAVIS_REPO_SLUG" = "tldr-pages/tldr" ] && [ "$TRAVIS_PULL_REQUEST" != "false" ]; then
   check_diff

scripts/test.sh

@@ -17,7 +17,7 @@ function run_tests {
 # Special test function for Travis CI pull request builds.
 # Runs run_tests collecting errors for tldr-bot.
 function run_tests_pr {
-  errs=`run_tests 2>&1`
+  errs=$(run_tests 2>&1)
 
   if [ -n "$errs" ]; then
     echo -e "Test failed!\n$errs\n" >&2
@@ -30,7 +30,7 @@ function run_tests_pr {
 # Additional checks for Travis CI pull request builds.
 # Only taken as suggestions, does not make the build fail.
 function run_checks_pr {
-  msgs=`bash scripts/check-pr.sh`
+  msgs=$(bash scripts/check-pr.sh)
 
   if [ -n "$msgs" ]; then
     echo -e "\nCheck PR reported the following message(s):\n$msgs\n" >&2