diff --git a/.build.sh b/.build.sh
new file mode 100644
index 0000000..31b14ea
--- /dev/null
+++ b/.build.sh
@@ -0,0 +1,25 @@
+#!/bin/echo Must be sourced from a bash script **
+
+# strict mode
+export IFS=$'\n'
+set -eu -o pipefail
+
+# git clone wrapper
+clone () {
+  if ! [ -e "$2" ]; then
+    git clone \
+      --single-branch --depth 1 \
+      --recurse-submodules \
+      "$1" \
+      "$2"
+  else
+    echo " ** '$2/' already exists"
+  fi
+}
+
+# make -j12
+make_maxthreads() {
+  [ -v JOBS ] || JOBS=$(nproc || echo 4)
+  JOBS="${JOBS//[^0-9]/}"
+  make -j"$JOBS"
+}
diff --git a/build_dig.sh b/build_dig.sh
index 89bede2..bf3461e 100755
--- a/build_dig.sh
+++ b/build_dig.sh
@@ -1,7 +1,6 @@
 #!/bin/bash
 
-IFS=$'\n'
-set -eu -o pipefail
+source .build.sh
 
 echo
 echo '==> Checking deps'
@@ -12,13 +11,10 @@ which gcc || which clang
 
 echo
 echo '==> Cloning repo'
-if ! [ -e bind9 ]; then
-  git clone --single-branch --depth 1 https://gitlab.isc.org/isc-projects/bind9.git bind9
-else
-  echo ' ** bind9/ already exists'
-fi
+clone https://gitlab.isc.org/isc-projects/bind9.git bind9
 
 cd bind9
+trap 'cd ..' EXIT
 export CFLAGS="-O3" CPPFLAGS="-O3"
 
 echo
@@ -38,10 +34,7 @@ echo '==> ./configure (check deps, generate config)'
 
 echo
 echo '==> make'
-make -j$(nproc)
-
-unset CFLAGS CPPFLAGS
-cd ..
+make_maxthreads
 
 echo
 echo '==> Done'
diff --git a/build_drill.sh b/build_drill.sh
index 8d91f9c..cf020a2 100755
--- a/build_drill.sh
+++ b/build_drill.sh
@@ -1,7 +1,6 @@
 #!/bin/bash
 
-IFS=$'\n'
-set -eu -o pipefail
+source .build.sh
 
 echo
 echo '==> Checking deps'
@@ -13,13 +12,10 @@ which gcc || which clang
 
 echo
 echo '==> Cloning repo'
-if ! [ -e ldns ]; then
-  git clone --single-branch --depth 1 --recurse-submodules https://github.com/NLnetLabs/ldns.git ldns
-else
-  echo ' ** ldns/ already exists'
-fi
+clone https://github.com/NLnetLabs/ldns.git ldns
 
 cd ldns
+trap 'cd ..' EXIT
 export CFLAGS="-O3"
 
 echo
@@ -42,10 +38,7 @@ echo '==> ./configure (check deps, generate config)'
 
 echo
 echo '==> make'
-make -j$(nproc || echo 4)
-
-unset CFLAGS
-cd ..
+make_maxthreads
 
 echo
 echo '==> Done'
diff --git a/build_hr.sh b/build_hr.sh
index 477c756..9fb25f3 100755
--- a/build_hr.sh
+++ b/build_hr.sh
@@ -1,7 +1,6 @@
 #!/bin/bash
 
-IFS=$'\n'
-set -eu -o pipefail
+source .build.sh
 
 echo
 echo '==> Checking deps'
@@ -10,18 +9,19 @@ which cargo
 
 echo
 echo '==> Cloning repo'
-git clone --single-branch --depth 1 https://github.com/hickory-dns/hickory-dns.git hickory-dns
+clone https://github.com/hickory-dns/hickory-dns.git hickory-dns
+
+cd hickory-dns
+trap 'cd ..' EXIT
 
 echo
 echo '==> Building resolve'
-cd hickory-dns
 cargo build \
   --release \
   --bin resolve \
   --features dnssec-ring \
   --config 'panic="abort"' \
   --config 'lto="fat"'
-cd ..
 
 echo
 echo '==> Done'