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Piping output into a 2nd command

SuperKarateMonkey
on
Medium Priority
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Last Modified: 2010-04-22
Gentlemen:

I'm trying to pipe the output of a find command into a 2nd command, which is to say that I want to cd over to the directory I already found with my find command, something like this:

find / -name mydir1 | cd $1

Does this work?  Do I need to use a different variable substitution?  What is the variable that indicates the piped in input?  Also, What if I'm looking for an individual file, and I want to cd to it's parent directory, like this:

find / -name myfile1 | cd $1

I know that won't work, since it's sending a file, not a directory to cd, but how do I get only the file?  Must I grep it out?
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Top Expert 2004

Commented:
Hi SuperKarateMonkey,
The problem is that you *could* find several of those.

If you're sure you won't, you could do:
cd `find / -name mydir1`


Cheers,
Stefan
Top Expert 2004

Commented:
SuperKarateMonkey,
> Does this work?

No. What you can do with "normal" commands is for example:
find / -name mydir1 | xargs ls -ltr

...but cd isn't a "normal" command: It cannot be external (that is being a separate binary that runs in a separate process), because each process has its own working directory and changeing the working directory first and then exiting the new process will not change the directory of the calling process (the shell).

The same happens when you do cd in a subshell:

(cd some_dir ; ls -l)

This will also not modify the original shells working directory. Sometimes this "subshell cd" comes in handy, as here:

tar -cf - | (cd /tmp; tar -xf - )

...but in your case it won't.

Stefan
Top Expert 2004

Commented:
SuperKarateMonkey,
> What is the variable that indicates the piped in input?
It's not a variable, it's the standard output of the process on the left side of the pipe which becomes the standard input of the process on the right side of the pipe. If you want to set variables, you'd do:

var=`some_command`
echo $var | some_other_command

...but you'd better use...

some_command | some_other_command

...unless you did some modifications on $var inbetween.

Stefan
Top Expert 2004

Commented:
SuperKarateMonkey,
> find / -name myfile1 | cd $1

For this, you need two levels of output converted to arguments (assuming you're using sh, bash or ksh):

cd $( dirname $( find / -name myfile1 ) )

Stefan

Author

Commented:
I guess what I'm asking is if there's an environment variable to indicate the output of the previous command, or if I can use piping to create one.

As for cd 'find / -name mydir1'

That didn't work.  The shell pukes, reporting:

cd: find / -name mydir1: No suck file or directory

Author

Commented:
Stefan:

You wrote:
cd $( dirname $( find / -name myfile1 ) )

YUP!  That's the stuff!  Just to make things clear, though, confirm I have these two postulates correct:

1.  Wrapping a command in () parentheses causes it to be executed as a unit?

2.  Putting a $ dollar sign ahead of said parentheses causes the command to be evaluated not by it's return value, (of usually 0 or 1,) but rather of it's output to standard out?

The reason I ask is that this is also working:

cd $(find / -name myfile1 -printf %h)
Top Expert 2004
Commented:
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Author

Commented:
Ohhhhh....  That's why your first answer didn't work.  I was using 'single quotes,' not `back ticks.`

Okey.  That pretty much covers it.  Thanks very much for your help, stefan72.
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