[목차] 1. 산술연상 expr, let 2. while and until loop 3. for-loop 1. 산술연상 expr, let expr - 정수형 산술연산(+,-,*,/,%), 논리연산(|,&), 관계연상(=,!=,>,>=, /dev/null echo $? # 2 cat > newuser #!/bin/bash #Description: Create a user account. echo -n "New username: " read username while getent passwd $username &> /dev/null do echo "Sorry, that account $username is already taken. Please pick a different username." echo -n..