How to execute the output of a command within the current shell?

The eval command exists for this very purpose.

eval "$( ls | sed... )"

More from the bash manual:

eval

          eval [arguments]

The arguments are concatenated together into a single command, which is then read and executed, and its exit status returned as the exit status of eval. If there are no arguments or only empty arguments, the return status is zero.

$ ls | sed ... | source /dev/stdin

UPDATE: This works in bash 4.0, as well as tcsh, and dash (if you change source to .). Apparently this was buggy in bash 3.2. From the bash 4.0 release notes:

Fixed a bug that caused `.' to fail to read and execute commands from non-regular files such as devices or named pipes.

Wow, I know this is an old question, but I've found myself with the same exact problem recently (that's how I got here).

Anyway - I don't like the source /dev/stdin answer, but I think I found a better one. It's deceptively simple actually:

echo ls -la | xargs xargs

Nice, right? Actually, this still doesn't do what you want, because if you have multiple lines it will concat them into a single command instead of running each command separately. So the solution I found is:

ls | ... | xargs -L 1 xargs

the -L 1 option means you use (at most) 1 line per command execution. Note: if your line ends with a trailing space, it will be concatenated with the next line! So make sure each line ends with a non-space.

Finally, you can do

ls | ... | xargs -L 1 xargs -t

to see what commands are executed (-t is verbose).

Hope someone reads this!