UNIX for Dummies Questions & Answers

enter "record:"
read rec
grep -qF "$rec" somefile
rc=$?
if [ $rc -eq 0 ]; then
    # whatever the user entered exists in somefile
    # take appropriate action/ no action
else
    # whatever user enter DOES NOT exist in the file somefile
    # do stuff here
fi

record_file=/path/to/some/file.txt

record_exists() {
    awk -v "record=$1" 'index($0,record) {found=1;exit} END {exit !found}' "$record_file"
}

read record
if record_exists "$record"; then
  #do stuff
else
  #do other stuff
fi

user_exists() {
    awk -F: -v "user=$1" '$1 == user {found=1;exit} END {exit !found}' /etc/passwd
}