Shell Logic

Conditional Logic

if [ TEST ]; then
  echo "TEST is true"
elif grep /path/to/file --fixed-strings foo >/dev/null; then
  echo "TEST is false and '/path/to/file' contains 'foo'"
else
  echo "TEST is false and '/path/to/file' does not contain 'foo'"
fi

Shell tests are typically used as the condition (as seen above), but any command that sets the exit code in the expected pattern (zero for true, non-zero for false; as seen above with grep(1)) can be used.

Conditional Commands

To execute a command conditionally after another command, try:

true && echo "This only executes because the first command set an exit code of 0"

false || echo "This only executes because the first command set an exit code of 1"

These operators have equal precedence.

Case Switching Logic

case $INPUT_STRING in
  y)
    echo "Proceeding..."
    ;;
  n)
    echo "Quitting..."
    ;;
  *)
    echo "Please enter y or n only"
    ;;
esac

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