With using command line;
1test -f /etc/os-release && echo "file exist"
2
3[ -f /etc/os-release ] && echo "file exist"
4
5[[ -f /etc/os-release ]] && echo "file exist"
With in a Bash script;
1FILE=/etc/os-release
2if [ -f "$FILE" ]; then
3 echo "$FILE exists."
4else
5 echo "$FILE does not exist."
6fi