Using grep and sed to find and replace a string

I am using the following to search a directory recursively for specific string and replace it with another:

grep -rl oldstr path | xargs sed -i 's/oldstr/newstr/g'

This works okay. The only problem is that if the string doesn't exist then sed fails because it doesn't get any arguments. This is a problem for me since i'm running this automatically with ANT and the build fails since sed fails.

Is there a way to make it fail-proof in case the string is not found?

I'm interested in a one line simple solution I can use (not necessarily with grep or sed but with common unix commands like these).

You can use find and -exec directly into sed rather than first locating oldstr with grep. It's maybe a bit less efficient, but that might not be important. This way, the sed replacement is executed over all files listed by find, but if oldstr isn't there it obviously won't operate on it.

find /path -type f -exec sed -i 's/oldstr/newstr/g' {} \;

Your solution is ok. only try it in this way:

files=$(grep -rl oldstr path) && echo $files | xargs sed....

so execute the xargs only when grep return 0, e.g. when found the string in some files.

Standard xargs has no good way to do it; you're better off using find -exec as someone else suggested, or wrap the sed in a script which does nothing if there are no arguments. GNU xargs has the --no-run-if-empty option, and BSD / OS X xargs has the -L option which looks like it should do something similar.