feat: add 'bak' script

dots/.bin/bak

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+
+# back up a file by copying it to a new file with a .bak extension
+# reference: https://askubuntu.com/questions/962489/is-there-any-way-to-create-backup-copy-of-a-file-without-type-its-name-twice
+
+usage() {
+  echo "Usage: bak [-t|--timestamp] <file to back up>"
+  exit 1
+}
+
+timestamp=false
+
+while [[ $# -gt 0 ]]; do
+  case $1 in
+    -t|--timestamp)
+      timestamp=true
+      shift
+      ;;
+    *)
+      break
+      ;;
+  esac
+done
+
+[ $# -eq 1 ] || usage
+
+if $timestamp; then
+  date="$(date +%Y-%m-%d_%H-%M-%S)"
+  cp -vpn "$1"{,."$date".bak}
+else
+  cp -vpn "$1"{,.bak}
+fi