Multiple conditions

3 snippets across 3 stacks — Bash & Linux, JavaScript, SQL

SHBash & Linux

Case Statement

syntax

case $variable in
  pattern1) commands ;;
  pattern2) commands ;;
  *) default ;;
esac

example

case "$1" in
  start)
    echo "Starting service..."
    systemctl start myapp
    ;;
  stop|restart)
    echo "${1}ing service..."
    systemctl "$1" myapp
    ;;
  status)
    systemctl status myapp
    ;;
  *)
    echo "Usage: $0 {start|stop|restart|status}"
    exit 1
    ;;
esac

Note Each branch ends with ;;. Patterns support globbing and | for alternatives. case is cleaner than long if/elif chains when matching a single variable against many values. *) is the default/catch-all branch.

JSJavaScript

switch Statement

JS · Control Flow

syntax

switch (expression) {
  case value: ... break;
  default: ...
}

example

function getStatusText(code) {
  switch (code) {
    case 200: return "OK";
    case 301: return "Moved Permanently";
    case 404: return "Not Found";
    case 500: return "Internal Server Error";
    default:  return `Unknown (${code})`;
  }
}
console.log(getStatusText(404));

output

"Not Found"

Note Uses strict equality (===). Forgetting break causes fall-through to the next case. Using return instead of break is a clean pattern in functions.

SQLSQL

AND, OR, NOT

SQL · Filtering

syntax

WHERE condition1 AND condition2
WHERE condition1 OR condition2
WHERE NOT condition

example

SELECT first_name, city, is_active
FROM users
WHERE (city = 'Seattle' OR city = 'Portland')
  AND NOT is_active = false;

output

-- Active users in Seattle or Portland

Note AND binds tighter than OR. Always use parentheses to make precedence explicit. WHERE a OR b AND c means WHERE a OR (b AND c), which trips people up.