check if exists bash code example

Example 1: .sh script: check if file exist

#!/bin/bash
if [ -e x.txt ]
then
    echo "ok"
else
    echo "nok"
fi

Example 2: bash check if string does not exist in file

Just use grep with flags 'F' (fixed string), 'x' (exact match) and 'q'
(quiet output) in order to check if a word string is in a file
if ! grep -Fxq "string" file.txt; then #do some code...#; fi