Batch File Variables

Variables

Variables are defined with set and accessed by surrounding a variable's name with percent signs (%).

Best practice is to quote variable substitutions.

set foo=bar
IF "%foo%"=="bar" ECHO Equal

Escaping Special Character

Special characters are escaped using the4 caret (^).

set foo=bar ^| baz

As with Unix scripting, when commands spawn subshells that re-interpret tokens, it becomes necessary to add an escaped escape character for each layer.

echo foo ^^^& bar | subroutine

Double-quoted strings are also interpreted literally.

Escaping Double Quotes

Because double-quoted strings are interpreted literally, there is further complication for double-quoted strings containing double quotes.

There is no universal solution as cmd.exe defers interpretation. Consult the specific commands to see if double quotes should be duplicated...

set foo="foo ""bar"" baz"

...or should be escaped in the Unix style...

set foo="foo \"bar\" baz"

Unset Variables

If a variable is not set, no substitution occurs.

set MyVar=
echo %MyVar%

This prints %MyVar%.

The same behavior will be seen internally, as in conditional statement.

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