use bashrc for start

line_in_file.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+set -v
+set -e
+
+LINE=$1
+FILE=$2
+DETECT=${3:-$LINE}
+
+if [[ -z $(grep "$DETECT" "$FILE") ]]; then
+    echo "Line not found in $FILE"
+    echo "$LINE" >> "$FILE"
+else
+    echo "Line already exists in $FILE"
+fi