why does bash exist code example

Example 1: check if file exists bash

FILE=/etc/resolv.conf
if [ -f "$FILE" ]; then
    echo "$FILE exists."
else 
    echo "$FILE does not exist."
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