diff --git a/tools/tools/git/git-arc.sh b/tools/tools/git/git-arc.sh
--- a/tools/tools/git/git-arc.sh
+++ b/tools/tools/git/git-arc.sh
@@ -43,6 +43,14 @@
     exit 1
 }
 
+cleanup()
+{
+    rc=$?
+    rm -fr "$GITARC_TMPDIR"
+    trap - EXIT
+    exit $rc
+}
+
 err_usage()
 {
     cat >&2 <<__EOF__
@@ -236,12 +244,11 @@
         err "invalid diff ID $diff"
     fi
 
-    tmp=$(mktemp)
+    tmp="${GITARC_TMPDIR}/tmp"
     echo '{"names":["'"$diff"'"]}' |
         arc_call_conduit -- phid.lookup > "$tmp"
     phid=$(jq -r ".response[].phid" "$tmp")
     if [ -z "$phid" ] || [ "$phid" = "null" ]; then
-        rm -f "$tmp"
         err "invalid Phabricator ID for ${diff}"
     fi
 
@@ -255,7 +262,6 @@
     summary=$(jq -r "select(.response != []) |
         .response.${diff}.fullName" < "$tmp")
     printf "${term_color}%-15s\033[0m %s\n" "${status_name}" "${summary}"
-    rm -f "$tmp"
 }
 
 log2diff()
@@ -328,7 +334,7 @@
         return 1
     fi
 
-    msg=$(mktemp)
+    msg="${GITARC_TMPDIR}/msg"
     git show -s --format='%B' "$commit" > "$msg"
     printf "\nTest Plan:\n" >> "$msg"
     printf "\nReviewers:\n" >> "$msg"
@@ -357,7 +363,6 @@
             ]}' |
             arc_call_conduit -- differential.revision.edit >&3
     fi
-    rm -f "$msg"
     return 0
 }
 
@@ -377,7 +382,7 @@
         jq '.response.data[0].attachments.reviewers.reviewers[] | select(.status == "accepted").reviewerPHID')
     if [ -n "$userids" ]; then
         echo '{
-        "constraints": {"phids": ['"$(printf "%s" "$userids" | tr '[:space:]' ',')"']}
+        "constraints": {"phids": ['"$(echo "$userids" | tr '[:blank:]' ',')"']}
         }' |
         arc_call_conduit -- user.search |
         jq -r '.response.data[].fields.username'
@@ -591,31 +596,30 @@
 
 patch_commit()
 {
-    local diff reviewid review_data authorid user_data user_addr user_name author
-    local tmp author_addr author_name
+    local diff reviewid review_data authorid user_data user_addr user_name
+    local diff_data author_addr author_name author tmp
 
     diff=$1
     reviewid=$(diff2phid "$diff")
     # Get the author phid for this patch
-    review_data=$(mktemp)
+    review_data="${GITARC_TMPDIR}/review"
     echo '{"constraints": {"phids": ["'"$reviewid"'"]}}' | \
         arc_call_conduit -- differential.revision.search > "$review_data"
     authorid=$(jq -r '.response.data[].fields.authorPHID' "$review_data")
     # Get metadata about the user that submitted this patch
-    user_data=$(mktemp)
+    user_data="${GITARC_TMPDIR}/user"
     echo '{"constraints": {"phids": ["'"$authorid"'"]}}' | \
         arc_call_conduit -- user.search | \
         jq -r '.response.data[].fields' > "$user_data"
     user_addr=$(jq -r '.username' "$user_data")
     user_name=$(jq -r '.realName' "$user_data")
-    rm "$user_data"
     # Dig the data out of querydiffs api endpoint, although it's deprecated,
     # since it's one of the few places we can get email addresses. It's unclear
     # if we can expect multiple difference ones of these. Some records don't
     # have this data, so we remove all the 'null's. We sort the results and
     # remove duplicates 'just to be sure' since we've not seen multiple
     # records that match.
-    diff_data=$(mktemp)
+    diff_data="${GITARC_TMPDIR}/diff"
     echo '{"revisionIDs": [ '"${diff#D}"' ]}' | \
         arc_call_conduit -- differential.querydiffs |
         jq -r '.response | flatten | .[]' > "$diff_data"
@@ -632,7 +636,6 @@
     fi
 
     author=$(find_author "$user_addr" "$user_name" "$author_addr" "$author_name")
-    rm "$diff_data"
 
     # If we had to guess, and the user didn't want to guess, abort
     if [ "${author}" = "ABORT" ]; then
@@ -640,12 +643,11 @@
         exit 1
     fi
 
-    tmp=$(mktemp)
-    jq -r '.response.data[].fields.title' "$review_data" > $tmp
-    echo >> $tmp
-    jq -r '.response.data[].fields.summary' "$review_data" >> $tmp
-    echo >> $tmp
-    rm "$review_data"
+    tmp="${GITARC_TMPDIR}/tmp"
+    jq -r '.response.data[].fields.title' "$review_data" > "$tmp"
+    echo >> "$tmp"
+    jq -r '.response.data[].fields.summary' "$review_data" >> "$tmp"
+    echo >> "$tmp"
     # XXX this leaves an extra newline in some cases.
     reviewers=$(diff2reviewers "$diff" | sed '/^$/d' | paste -sd ',' - | sed 's/,/, /g')
     if [ -n "$reviewers" ]; then
@@ -654,7 +656,6 @@
     # XXX TODO refactor with gitarc__stage maybe?
     printf "Differential Revision:\thttps://reviews.freebsd.org/%s\n" "${diff}" >> "$tmp"
     git commit --author "${author}" --file "$tmp"
-    rm "$tmp"
 }
 
 gitarc__patch()
@@ -714,7 +715,7 @@
         git checkout -q -b "${branch}" main
     fi
 
-    tmp=$(mktemp)
+    tmp="${GITARC_TMPDIR}/tmp"
     for commit in $commits; do
         git show -s --format=%B "$commit" > "$tmp"
         title=$(git show -s --format=%s "$commit")
@@ -875,4 +876,7 @@
     BROWSE=--browse
 fi
 
+GITARC_TMPDIR=$(mktemp -d)
+trap cleanup EXIT HUP INT QUIT TRAP USR1 TERM
+
 gitarc__"${verb}" "$@"