Split long commands in multiple lines through Windows batch file

Question

You can break up long lines with the caret ^ as long as you remember that the caret and the newline following it are completely removed. So, if there should be a space where you're breaking the line, include a space. (More on that below.)

Example:

copy file1.txt file2.txt

would be written as:

copy file1.txt^
 file2.txt

The rule for the caret is:

A caret at the line end, appends the next line, the first character of the appended line will be escaped.

You can use the caret multiple times, but the complete line must not exceed the maximum line length of ~8192 characters (Windows XP, Windows Vista, and Windows 7).

echo Test1
echo one ^
two ^
three ^
four^
*
--- Output ---
Test1
one two three four*

echo Test2
echo one & echo two
--- Output ---
Test2
one
two

echo Test3
echo one & ^
echo two
--- Output ---
Test3
one
two

echo Test4
echo one ^
& echo two
--- Output ---
Test4
one & echo two

To suppress the escaping of the next character you can use a redirection.

The redirection has to be just before the caret. But there exist one curiosity with redirection before the caret.

If you place a token at the caret the token is removed.

echo Test5
echo one <nul ^
& echo two
--- Output ---
Test5
one
two


echo Test6
echo one <nul ThisTokenIsLost^
& echo two
--- Output ---
Test6
one
two

And it is also possible to embed line feeds into the string:

setlocal EnableDelayedExpansion
set text=This creates ^

a line feed
echo Test7: %text%
echo Test8: !text!
--- Output ---
Test7: This creates
Test8: This creates
a line feed

The empty line is important for the success. This works only with delayed expansion, else the rest of the line is ignored after the line feed.

It works, because the caret at the line end ignores the next line feed and escapes the next character, even if the next character is also a line feed (carriage returns are always ignored in this phase).

(This is basically a rewrite of Wayne's answer but with the confusion around the caret cleared up. So I've posted it as a CW. I'm not shy about editing answers, but completely rewriting them seems inappropriate.)

You can break up long lines with the caret (^), just remember that the caret and the newline that follows it are removed entirely from the command, so if you put it where a space would be required (such as between parameters), be sure to include the space as well (either before the ^, or at the beginning of the next line — that latter choice may help make it clearer it's a continuation).

Examples: (all tested on Windows XP and Windows 7)

xcopy file1.txt file2.txt

can be written as:

xcopy^
 file1.txt^
 file2.txt

or

xcopy ^
file1.txt ^
file2.txt

or even

xc^
opy ^
file1.txt ^
file2.txt

(That last works because there are no spaces betwen the xc and the ^, and no spaces at the beginning of the next line. So when you remove the ^ and the newline, you get...xcopy.)

For readability and sanity, it's probably best breaking only between parameters (be sure to include the space).

Be sure that the ^ is not the last thing in a batch file, as there appears to be a major issue with that.

Multiple commands can be put in parenthesis and spread over numerous lines; so something like echo hi && echo hello can be put like this:

( echo hi
  echo hello )

Also variables can help:

set AFILEPATH="C:\SOME\LONG\PATH\TO\A\FILE"
if exist %AFILEPATH% (
  start "" /b %AFILEPATH% -option C:\PATH\TO\SETTING...
) else (
...

Also I noticed with carets (^) that the if conditionals liked them to follow only if a space was present:

if exist ^

It seems however that splitting in the middle of the values of a for loop doesn't need a caret(and actually trying to use one will be considered a syntax error). For example,

for %n in (hello
bye) do echo %n

Note that no space is even needed after hello or before bye.

One thing I did not find when searching for 'how to split a long DOS batch file line' was how to split something containing long quoted text. In fact it IS covered in the answers above, but is not obvious. Use Caret to escape them. e.g.

myprog "needs this to be quoted"

can be written as:

myprog ^"needs this ^
to be quoted^"

but beware of starting a line with Caret after ending a line with caret - because it will come out as caret..?:

echo ^"^
needs this ^
to be quoted^
^"

-> "needs this to be quoted^"