CODEWITHSUNDEEP
windowscmdescapingecho
code_onkel
code_onkel

Reputation: 2947

Windows echo command: The odds of cmd.exe escaping

I'm in the unfortunate position to be forced to invoke a program via echo <input> | program.exe. Of course, I wondered how to escape <input> and found:

In essence, it seems sufficient to escape all special chars with ^. Out of curiosity I still would like to know, why echo ingores double-quote escaping in the first place:

C:\>echo "foo"
"foo"

C:\>

Is there any normative reference?

Bonus question: How to echo the strings on and off with the echo command?

Edit: I just found this. I states that only |<> need to be escaped. However, expansion like %FOO% still work.

Upvotes: 0

Views: 468

Answers (1)

aschipfl
aschipfl

Reputation: 34979

Special characters like ^, &, (, ), <, >, %, ! and " may cause problems with echo, also when trying to echo a string into a pipe; odd numbers of " are particularly difficult to handle.

Building escape sequences can be very complicated particularly with pipes, because such initiates new cmd instances for either side, so multi-escaping might become necessary.

The only reliable way to pipe the output of echo into a program is to use a variable holding the string to return and to apply delayed expansion, but within the left side of the pipe, like this:

cmd /V /C echo(^^!VARIABLE^^!| program.exe

Note the double-escaping of ! like ^^!, which makes this code even work when delayed expansion is also enabled in the parent cmd instance. There must not be a SPACE in front of the |, because this was echoed too otherwise. Note that echo terminates the output by a line-break.

Upvotes: 1

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