如果在反斜杠之后和换行符之前有空格(空格或制表符¹)，续行将失败。没有这样的空白，你的例子为我工作良好:

$ cat test.sh
if ! fab --fabfile=.deploy/fabfile.py \
   --forward-agent \
   --disable-known-hosts deploy:$target; then
     echo failed
else
     echo succeeded
fi

$ alias fab=true; . ./test.sh
succeeded
$ alias fab=false; . ./test.sh
failed

Some detail promoted from the comments: the line-continuation backslash in the shell is not really a special case; it is simply an instance of the general rule that a backslash "quotes" the immediately-following character, preventing any special treatment it would normally be subject to. In this case, the next character is a newline, and the special treatment being prevented is terminating the command. Normally, a quoted character winds up included literally in the command; a backslashed newline is instead deleted entirely. But otherwise, the mechanism is the same. Most importantly, the backslash only quotes the immediately-following character; if that character is a space or tab, you just get a literal space or tab; the backslash will have no effect on a subsequent newline.

¹或回车，就像捷克学指出的那样。POSIX shell不适合windows格式的文本文件，甚至在WSL中也不行。或者Cygwin，但至少他们的Bash端口增加了一个igncr选项，你可以设置-o使其容忍回车。

对于Windows/WSL/Cygwin等用户:

确保你的行结束符是标准的Unix换行符，也就是只使用\n (LF)。

使用Windows行结束符\r\n (CRLF)行结束符将中断命令行换行符。

这是因为将\放在一行的末尾，而Windows行的末尾则转换为 \ \r \n。 正如Mark在上面正确解释的那样:

如果在反斜杠之后和换行符之前有空格，行延续将失败。

这不仅包括空格符()或制表符(\t)，还包括回车符(\r)。