Recursively rename files using find and sed

This happens because sed receives the string {} as input, as can be verified with:

find . -exec echo `echo "{}" | sed 's/./foo/g'` \;

which prints foofoo for each file in the directory, recursively. The reason for this behavior is that the pipeline is executed once, by the shell, when it expands the entire command.

There is no way of quoting the sed pipeline in such a way that find will execute it for every file, since find doesn't execute commands via the shell and has no notion of pipelines or backquotes. The GNU findutils manual explains how to perform a similar task by putting the pipeline in a separate shell script:

#!/bin/sh
echo "$1" | sed 's/_test.rb$/_spec.rb/'

(There may be some perverse way of using sh -c and a ton of quotes to do all this in one command, but I'm not going to try.)

you might want to consider other way like

for file in $(find . -name "*_test.rb")
do 
  echo mv $file `echo $file | sed s/_test.rb$/_spec.rb/`
done

To solve it in a way most close to the original problem would be probably using xargs "args per command line" option:

find . -name "*_test.rb" | sed -e "p;s/test/spec/" | xargs -n2 mv

It finds the files in the current working directory recursively, echoes the original file name (p) and then a modified name (s/test/spec/) and feeds it all to mv in pairs (xargs -n2). Beware that in this case the path itself shouldn't contain a string test.