diff --git a/scripts/download_all.sh b/scripts/download_all.sh
index edd96a2..ebcc26f 100755
--- a/scripts/download_all.sh
+++ b/scripts/download_all.sh
@@ -3,35 +3,44 @@
 # Guard clause check if required binaries are installed
 which wget > /dev/null || { echo "Error: wget not installed." ; exit 1 ; }
 which egrep > /dev/null || { echo "Error: egrep not installed." ; exit 1 ; }
-which xargs > /dev/null || { echo "Error: xargs not installed." ; exit 1 ; }
 
 # Recursively traverse directories in repo scraping markdown file for URLs
 # containing pdfs. Downloads pdfs into respective directories.
 download_for_directory() {
-    cd $1
+    cd $1 || { echo "Error: directory not found." ; exit 1 ; }
+
     for f in *; do
-        if [ -d "$f" ]; then
-            download_for_directory $f &
+        if [[ -d ${f} ]]; then
+            download_for_directory ${f} &
         fi
     done
 
-    ls | cat *.md 2> /dev/null \
-    | egrep -o 'https?://[^ ]+' \
-    | grep 'pdf' | tr -d ')' \
-    | xargs --no-run-if-empty wget --no-clobber --quiet --timeout=5 --tries=2
+    # Scrape URLs from markdown files
+    urls=$(ls | cat *.md 2> /dev/null | egrep -o 'https?://[^ ]+' | grep 'pdf' | tr -d ')')
+
+    for url in "$urls"; do
+        # Ignore empty URLs
+        if [[ ! -z ${url} ]]; then
+            wget ${url} --no-clobber --quiet --timeout=5 --tries=2
+        fi
+    done
     
     cd ..
     echo "$1 done."
 }
 
-if [ "$#" -ne 1 ]; then
-    BASEDIR="$(dirname $0)/.."
-    download_for_directory $BASEDIR
+# If no directories are supplied, iterate over the entire repo.
+if [[ "$#" -ne 1 ]]; then
+    REPO_ROOT_DIR="$(dirname $0)/.."
+    download_for_directory ${REPO_ROOT_DIR}
 else
+# Iterate over the specified directories
     for dir in "$@"
     do
-        download_for_directory $dir
+        download_for_directory ${dir}
     done
 fi
 
+# Wait for child processes to terminate
 wait
+