02-28-2009
Exclude Certain Entries from Piped or Redirected Output?
I want to execute a command something like:
find / -name "jni.h"
and I want to direct the output of that command to some type of
filter that will leave out all the lines reporting inaccessible
directories (permission unavailable). Is this a pipe or a redirect?
For example, output like the below is not useful to me:
$ find / -name "jni.h"
find: /.fseventsd: Permission denied
find: /.Spotlight-V100: Permission denied
find: /.Trashes: Permission denied
^C
I have been looking over awk, sed, grep and the like to no avail.
I know this is possible. I did it years ago when I worked in
a command line development environment but I'm having trouble
finding it again.
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POPEN(3) Library Functions Manual POPEN(3)
NAME
popen, pclose - initiate I/O to/from a process
SYNOPSIS
#include <stdio.h>
FILE *popen(const char *command, const char *type)
int pclose(FILE *stream)
DESCRIPTION
The arguments to popen are pointers to null-terminated strings containing respectively a shell command line and an I/O mode, either "r" for
reading or "w" for writing. It creates a pipe between the calling process and the command to be executed. The value returned is a stream
pointer that can be used (as appropriate) to write to the standard input of the command or read from its standard output.
A stream opened by popen should be closed by pclose, which waits for the associated process to terminate and returns the exit status of the
command.
Because open files are shared, a type "r" command may be used as an input filter, and a type "w" as an output filter.
SEE ALSO
pipe(2), fopen(3), fclose(3), system(3), wait(2), sh(1).
DIAGNOSTICS
Popen returns a null pointer if files or processes cannot be created, or the shell cannot be accessed.
BUGS
Buffered reading before opening an input filter may leave the standard input of that filter mispositioned. Similar problems with an output
filter may be forestalled by careful buffer flushing, for instance, with fflush, see fclose(3).
7th Edition May 15, 1985 POPEN(3)