How do I escape ampersands in batch files?

Question

& is used to separate commands. Therefore you can use ^ to escape the &.

From a cmd:

• & is escaped like this: ^& (based on @Wael Dalloul's answer)
• % does not need to be escaped

An example:

start http://www.google.com/search?client=opera^&rls=en^&q=escape+ampersand%20and%20percentage+in+cmd^&sourceid=opera^&ie=utf-8^&oe=utf-8

From a batch file

• & is escaped like this: ^& (based on @Wael Dalloul's answer)
• % is escaped like this: %% (based on the OPs update)

An example:

start http://www.google.com/search?client=opera^&rls=en^&q=escape+ampersand%%20and%%20percentage+in+batch+file^&sourceid=opera^&ie=utf-8^&oe=utf-8

You can enclose it in quotes, if you supply a dummy first argument.

Note that you need to supply a dummy first argument in this case, as start will treat the first argument as a title for the new console windows, if it is quoted. So the following should work (and does here):

start "" "http://www.google.com/search?client=opera&rls=en&q=escape+ampersand&sourceid=opera&ie=utf-8&oe=utf-8"

explorer "http://www.google.com/search?client=opera&rls=...."

The command

echo this ^& that

works as expected, outputing

this & that

The command

echo this ^& that > tmp

also works, writing the string to file "tmp". However, before a pipe

echo this ^& that | clip

the ^ is interpreted completely differently. It tries to write the output of the two commands "echo this" and "that" to the pipe. The echo will work then "that" will give an error. Saying

echo this ^& echo that | clip

will put the strings "this" and "that" on the clipboard.

Without the ^:

echo this & echo that | clip

the first echo will write to the console and only the second echo's output will be piped to clip (similarly for "> tmp" redirection). So, when output is being redirected, the ^ does not quote the & but instead causes it to be applied before the redirection rather than after.

To pipe an &, you have to quote it twice

echo this ^^^& that | clip

If you put the string in a variable

set m=this ^& that

then

set m

will output

m=this & that

but the obvious

echo %m%

fails because, after Windows substitutes the variable, resulting in

echo this & that

it parses this as a new command and tries to execute "that".

In a batch file, you can use delayed expansion:

setlocal enableDelayedExpansion
echo !m!

To output to a pipe, we have to replace all &s in the variable value with ^&, which we can do with the %VAR:FROM=TO% syntax:

echo !m:^&=^^^&! | clip

On the command line, "cmd /v" enables delayed expansion:

cmd /v /c echo !m!

This works even when writing to a pipe

cmd /v /c echo !m! | clip

Simple.