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Top Forums Shell Programming and Scripting How to launch results of a pipe? Post 302628965 by scampsd on Tuesday 24th of April 2012 07:54:58 AM
Old 04-24-2012
Question How to launch results of a pipe?

Good afternoon,
I have just messed up and deleted some directories on my UNIX machine.
I would now want to know which packages are impacted by this. Therefore I have a look in the file "/var/sadm/install/contents" (which contains the filenames/directory names for each installation package). After this, I add "ls " in front and "1>/dev/null" at the back, so I get following result:

Code:
$grep "<Package>" /var/sadm/install/contents | awk {'print "ls " $1 " 1>/dev/null"'}
...
ls /usr/3rdpty/ant/lib/ant.jar 1>/dev/null
ls /usr/3rdpty/ant/lib/xercesImpl.jar 1>/dev/null
ls /usr/3rdpty/ant/lib/xml-apis.jar 1>/dev/null
Now I would like to launch those "ls" commands. The idea is the following:
$ls <existing file> 1>/dev/null
$ls <non-existing file> 1>/dev/null
<non-existing file>: No such file or directory

=> I intend only to see which files/directories have been erased that belong to the package. When there are none, nothing needs to be done. When there are some, the package needs to be re-installed.

In order to do this, I need to launch the "ls ..." output.
I have already tried using a "| eval" behind it, but this does not work.
Does anybody have an idea?

Thanks
Dominique

Last edited by Scott; 04-24-2012 at 09:19 AM.. Reason: Code tags
 

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PIPE(2) 							System Calls Manual							   PIPE(2)

NAME
pipe - create an interprocess channel SYNOPSIS
pipe(fildes) int fildes[2]; DESCRIPTION
The pipe system call creates an I/O mechanism called a pipe. The file descriptors returned can be used in read and write operations. When the pipe is written using the descriptor fildes[1] up to 4096 bytes of data are buffered before the writing process is suspended. A read using the descriptor fildes[0] will pick up the data. Writes with a count of 4096 bytes or less are atomic; no other process can inter- sperse data. It is assumed that after the pipe has been set up, two (or more) cooperating processes (created by subsequent fork calls) will pass data through the pipe with read and write calls. The Shell has a syntax to set up a linear array of processes connected by pipes. Read calls on an empty pipe (no buffered data) with only one end (all write file descriptors closed) returns an end-of-file. SEE ALSO
sh(1), read(2), write(2), fork(2) DIAGNOSTICS
The function value zero is returned if the pipe was created; -1 if too many files are already open. A signal is generated if a write on a pipe with only one end is attempted. BUGS
Should more than 4096 bytes be necessary in any pipe among a loop of processes, deadlock will occur. ASSEMBLER
(pipe = 42.) sys pipe (read file descriptor in r0) (write file descriptor in r1) PIPE(2)
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