Using csh & tcsh

Quoting Oddities

The quoting rules have a few exceptions. You probably won't run into these often, but it's good to be aware of them:

• ! or $ at the end of an argument is not interpreted as special and does not need quoting:

  % echo x! x$
  x! x$

• A backslash inside quote marks is normally left alone, as demonstrated below where the quotes protect the backslash in the second and third arguments:

  % echo \x '\x' "\x"
  x \x \x

  However, if a backslash occurs before !, it is always interpreted as a quote character. Notice how the backslash disappears in the following example, even when it appears within quote marks:

  % echo \!x '\!x' "\!x"
  !x !x !x

  This result occurs because \ is the only way to turn off !; therefore, \! is interpreted as a literal ! regardless of its context.

• !, `, and $ normally retain their special meaning inside double quotes. You can turn off ! and ` (but not $) by preceding each with a backslash:

  % echo "\!x" "\`x\`"
  !x `x`
  % echo "\$shell"
  /bin/tcsh

  Inside double quotes, a $ is interpreted as beginning a variable reference, and you cannot turn it off, even with a backslash.

• A single quote cannot appear within a single-quoted string, even if you use a backslash. The same is true of double quotes within a double-quoted string:

  % echo '\''
  Unmatched '.
  % echo "\""
  Unmatched ".