dist/tools: fix shellcheck warnings in pr_check script

Author: crasbe

dist/tools/pr_check/check.sh

@@ -7,18 +7,19 @@
 # directory for more details.
 #
 
+# shellcheck source=/dev/null
 . "$(dirname "$0")/../ci/github_annotate.sh"
 
-: "${RIOTBASE:=$(cd $(dirname $0)/../../../; pwd)}"
-cd $RIOTBASE
+: "${RIOTBASE:="$(cd "$(dirname "$0")"/../../../ || exit; pwd)"}"
+cd "$RIOTBASE" || exit
 
 : "${RIOTTOOLS:=${RIOTBASE}/dist/tools}"
 
 EXIT_CODE=0
 
 github_annotate_setup
 
-if tput colors &> /dev/null && [ $(tput colors) -ge 8 ]; then
+if tput colors &> /dev/null && [ "$(tput colors)" -ge 8 ]; then
     CERROR="\e[1;31m"
     CRESET="\e[0m"
 else
@@ -40,12 +41,12 @@ keyword_filter() {
         -e "^    [0-9a-f]\+ .\{0,2\}Update"
 }
 
-SQUASH_COMMITS="$(git log $(git merge-base HEAD "${RIOT_MASTER}")...HEAD --pretty=format:"    %h %s" | \
+SQUASH_COMMITS="$(git log "$(git merge-base HEAD "${RIOT_MASTER}")"...HEAD --pretty=format:"    %h %s" | \
                   keyword_filter)"
 
 if [ -n "${SQUASH_COMMITS}" ]; then
     if github_annotate_is_on; then
-        echo "${SQUASH_COMMITS}" | while read commit; do
+        echo "${SQUASH_COMMITS}" | while read -r commit; do
             ANNOTATION="Commit needs to be squashed: \"${commit}\""
             ANNOTATION="${ANNOTATION}\n\nPLEASE ONLY SQUASH WHEN ASKED BY A "
             ANNOTATION="${ANNOTATION}MAINTAINER!"