UNIX for Dummies Questions & Answers

Hi:

how come this command does not work? the error message is:
xargs: cd: No such file or directory

yet, in the same time, 'echo dir_path | xargs ls' works.

Does it work in bash? We use csh.

Thanks.

NB Phil

No matter what your shell, cd is a shell builtin and not an executable. cd pretty much has to be a builtin; anything else wouldn't be able to change the shell's own current directory. Imagine spawning a process, changing that process' current directory, and waiting for it to return to find that your own current directory remains unchanged -- a /bin/cd program would be useless

Also, see csh programming considered harmful.

Hi Corona:

Thanks for the response.

we are stuck in csh not by our own choice.

Are you saying that the xargs only supply args to commands or utilities, not to built-ins? Since 'cd' is a built-in, so xargs can't find it?

Thanks.

Absolutely. Xargs is unaware of shell builtins as it launches the command itself and so is independent from any shell.
That wouldn't prevent your script to work on systems like Solaris that have cd as a command too. However, cd is expecting a single argument so there is no much point in using it through xargs.

Thanks for the reply. Did not realize the difference between built-in and commands until now.

Basically, the xargs only searches the commands within the search path.

xargs did not complain about "ls" though. But is "ls" a built-in too?

So I assume there is no way to let xargs search for built-in commands, am i correct?

Thanks.

"ls" might be a builtin but is always provided as a command. You can always wrap a built-in command with a script.

HP-UX have /usr/bin/cd , but it is a Posix shell script ! This still does not work with xargs so I looked deeper.

After testing with a script not called "cd" it became clear that xargs is passing the parameter correctly BUT the "cd" is executing in a sub shell and not being retained when control returns to the calling shell.

In most Posix shells this construct works because the "cd" is executed in the current shell. Somebody might be able to convert this to csh.

Code:

echo "/new_directory"|while read DIR
do
       cd "${DIR}"
       pwd
done