feature: add retry

retry

@@ -0,0 +1,36 @@
+#!/bin/bash
+
+# Retry a command up to a specific numer of times until it exits successfully,
+# with exponential back off.
+#
+#  $ retry 5 echo Hello
+#  Hello
+#
+#  $ retry 5 false
+#  Retry 1/5 exited 1, retrying in 1 seconds...
+#  Retry 2/5 exited 1, retrying in 2 seconds...
+#  Retry 3/5 exited 1, retrying in 4 seconds...
+#  Retry 4/5 exited 1, retrying in 8 seconds...
+#  Retry 5/5 exited 1, no more retries left.
+  
+function retry {
+  local retries=$1
+  shift
+
+  local count=0
+  until "$@"; do
+    exit=$?
+    wait=$((2 ** $count))
+    count=$(($count + 1))
+    if [ $count -lt $retries ]; then
+      echo "Retry $count/$retries exited $exit, retrying in $wait seconds..."
+      sleep $wait
+    else
+      echo "Retry $count/$retries exited $exit, no more retries left."
+      return $exit
+    fi
+  done
+  return 0
+}
+
+retry "$@"