feat: add fallback to /dev/tcp on bash if netcat not found

.drone.yml

@@ -12,11 +12,18 @@ steps:
     commands:
       - shellcheck ./wait-for
 
-  - name: test
+  - name: test-nc
     image: bats/bats
     commands:
       - bats ./wait-for.bats
 
+  - name: test-bash
+    image: bats/bats
+    commands:
+      - apk add bash
+      - rm -rf /usr/bin/nc
+      - bats ./wait-for.bats
+
 trigger:
   ref:
     - refs/heads/main

wait-for

@@ -3,6 +3,9 @@
 WAITFOR_TIMEOUT=${WAITFOR_TIMEOUT:-15}
 WAITFOR_QUIET=${WAITFOR_QUIET:-0}
 
+HAS_NC=0
+HAS_BASH=0
+
 echoerr() {
   if [ "$WAITFOR_QUIET" -ne 1 ]; then printf "%s\n" "$*" 1>&2; fi
 }
@@ -24,7 +27,12 @@ USAGE
 
 wait_for() {
   for _ in $(seq "$WAITFOR_TIMEOUT"); do
-    nc -w 1 -z "$WAITFOR_HOST" "$WAITFOR_PORT" >/dev/null 2>&1
+    if [ $HAS_NC = 1 ]; then
+      nc -w 1 -z "$WAITFOR_HOST" "$WAITFOR_PORT" >/dev/null 2>&1
+    elif [ $HAS_BASH = 1 ]; then
+      # shellcheck disable=SC3025
+      (echo >/dev/tcp/"$WAITFOR_HOST"/"$WAITFOR_PORT") >/dev/null 2>&1
+    fi
 
     result=$?
     if [ $result -eq 0 ]; then
@@ -73,8 +81,16 @@ while [ $# -gt 0 ]; do
   esac
 done
 
-if ! [ -x "$(command -v nc)" ]; then
-  echoerr "error: netcat is required for wait-for to run"
+if [ -x "$(command -v nc)" ]; then
+  HAS_NC=1
+fi
+
+if [ -x "$(command -v bash)" ]; then
+  HAS_BASH=1
+fi
+
+if [ $HAS_NC = 0 ] || [ $HAS_BASH = 0 ]; then
+  echoerr "error: netcat or bash is required for wait-for to run"
   exit 1
 fi