05-21-2009
cp output /dev/null results in not a directory
Hello,
I am working on a script to measure the read performance of a busybox environment. The logical choice is to use a command line like:
(time cp * /dev/null) 2> /tmp/howlong.txt
Ah, the rub is cp or /dev/null will only accept a single file at a time.
The result in the txt file is and output list that basically shows /dev/null/filename Not a directory.
I tried the same with using dd if=* of=/dev/null bs=1M, alas the results were similar.
I tried using a for loop, but I could not get time to work with syntax errors.
Example:
Works:
for FILE * cp $FILE /dev/null ; done
Fails:
(time for FILE * cp $FILE /dev/null ; done) 2> /tmp/howlong.txt
Any help here would be appreciated.
Thanks,
-Steve
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LEARN ABOUT FREEBSD
fdescfs
FDESCFS(5) BSD File Formats Manual FDESCFS(5)
NAME
fdescfs -- file-descriptor file system
SYNOPSIS
fdescfs /dev/fd fdescfs rw 0 0
DESCRIPTION
The file-descriptor file system, or fdescfs, provides access to the per-process file descriptor namespace in the global file system names-
pace. The conventional mount point is /dev/fd.
The file system's contents appear as a list of numbered files which correspond to the open files of the process reading the directory. The
files /dev/fd/0 through /dev/fd/# refer to file descriptors which can be accessed through the file system. If the file descriptor is open
and the mode the file is being opened with is a subset of the mode of the existing descriptor, the call:
fd = open("/dev/fd/0", mode);
and the call:
fd = fcntl(0, F_DUPFD, 0);
are equivalent.
Flags to the open(2) call other than O_RDONLY, O_WRONLY and O_RDWR are ignored.
Note: /dev/fd/0, /dev/fd/1 and /dev/fd/2 files are created by default when devfs alone is mounted. fdescfs creates entries for all file
descriptors opened by the process.
FILES
/dev/fd/#
EXAMPLES
To mount a fdescfs volume located on /dev/fd:
mount -t fdescfs null /dev/fd
SEE ALSO
devfs(5), mount(8)
HISTORY
The fdescfs file system first appeared in 4.4BSD. The fdescfs manual page first appeared in FreeBSD 2.2.
AUTHORS
The fdescfs manual page was written by Mike Pritchard <mpp@FreeBSD.org>, and was based on the manual page written by Jan-Simon Pendry.
BSD
September 18, 2010 BSD