How to use variables in sed on Windows?

Question

I'm writing a batch script to automate build events on Windows, and as part of it I need to change some lines in a few files. So I'm going to use sed. But how do I use variables in sed inside a batch script?

Solution

Refer to the variables using the usual %varname% syntax used by cmd.exe. As shown in this example, I've defined two variables old and new and substituted them into a sed expression on the command line. Typing original into the input, sed echos back new and improved.

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

c:\Users\Nicole>set old=original

c:\Users\Nicole>set new=new and improved

c:\Users\Nicole>sed "s/%old%/%new%/"
original
new and improved
^Z

Comments

[Ramhound]

How are you going to use a unix utility on Windows? What version of Windows are you using. We need more specifics.

[SSumner]

That would be another question. I'm using Win7, but I've been told I have to use sed for the modification of the files.

[SSumner]

And there are versions of sed for Windows: gnuwin32.sourceforge.net/packages/sed.htm

[David Ruhmann]

Do you have to use sed, No. Might it be easier to use sed, Yes. Just want to make sure you understand that you are not limited to just sed. See stackoverflow.com/questions/127318/…

[SSumner]

I'm told I have to use sed. I'm aware there are other ways to solve the problem, but those are the constraints I have been given

[Admin]

what is %new% contains backslashes? E.g., set new=c:\windows\system32\cmd.exe ? Sed wants to escape the characters and you end up with c:indowsystem32md.exe

[Admin]

@pbarney Escape the \ escape character. This is part of the sed syntax. Write it as set new=c:\\windows\\system32\\cmd.exe.

[Admin]

Thanks that helps, but what if you don't know the value? For example, if you're doing a character replacement on an environment variable with contains backslashes?

[Admin]

@pbarney If you're using a Unix shell on Windows that supports command substitution, you could use sed to replace all the \'s with two \'s, e.g., set escapenew = `echo $new | sed "s/\\/\\\\/g"`