/dev/null，外号叫无底洞，你可以向它输出任何数据，它通吃，并且不会撑着！
/dev/zero,是一个输入设备，你可你用它来初始化文件。
/dev/null------它是空设备，也称为位桶（bit bucket）。任何写入它的输出都会被抛弃。如果不想让消息以标准输出显示或写入文件，那么可以将消息重定向到位桶。
/dev/zero------该设备无穷尽地提供0，可以使用任何你需要的数目——设备提供的要多的多。他可以用于向设备或文件写入字符串0。
oracle@localhost oracle]$if=/dev/zero of=./test.txt bs=1k count=1
oracle@localhost oracle]$ ls -l
total 4
-rw-r--r-- 1 oracle dba 1024 Jul 15 16:56 test.txt
eg,
find / -name access_log 2>/dev/null
这样，一些诸如一些错误信息就不会显示出来。
==============================================================================
/dev/null：
In
Unix-like operating systems, /dev/null or the null device is a special
file that discards all data written to it, and provides no data to any
process that reads from it (it returns EOF). In Unix programmer jargon,
it may also be called the bit bucket or black hole.
The null
device is typically used for disposing of unwanted output streams of a
process, or as a convenient empty file for input streams. This is
usually done by redirection.
This entity is a common inspiration
for technical jargon expressions and metaphors by Unix programmers, e.g.
"please send complaints to /dev/null" or "my mail got archived in
/dev/null", being jocular ways of saying, respectively: "don't bother to
send any complaints" and "my mail got deleted". A famous advertisement
for the Titanium PowerBook G4 read [The Titanium Powerbook G4] Sends
other UNIX boxes to /dev/null.
The null device is also a favorite
subject of technical jokes, such as warning users that the system's
/dev/null is already 98% full. The April Fool's, 1995 issue of the
German magazine c't reported on an enhanced /dev/null chip that would
efficiently dispose of the incoming data by converting it to flicker on
an internal glowing LED.
/dev/null is a special file, not a
directory (folder), so one cannot move files into it with the Unix mv
command. See rm for the proper way to delete files in Unix.
The
equivalent device in CP/M (and later DOS and Windows) is called NUL:,
and on some versions of DOS just NUL (for example, one may hide output
by directing it to NUL, e.g. PAUSE>NUL, which waits for the user to
press any key without printing anything to the screen). Under classic
Amiga operating systems, the device's name is NIL:. In Windows NT and
its successors, it is named \Device\Null internally, though, the DOS NUL
is a symbolic link to it. Similarly, in OpenVMS the device is named
NL:.
/dev/zero：
In
Unix-like operating systems, /dev/zero is a special file that provides
as many null characters (ASCII NULL, 0x00; not ASCII character "digit
zero", "0", 0x30) as are read from it. One of the typical uses is to
provide a character stream for overwriting information. Another might be
to generate a clean file of a certain size. Using mmap to map /dev/zero
to RAM is the BSD way of implementing shared memory.
# Initialise partition (important note: trying out this command will eradicate
# any files that were on the partition, make sure you have a backup of any important data.)
dd if=/dev/zero of=/dev/hda7
# Create a large empty file called 'foobar'
dd if=/dev/zero of=foobar count=1000 bs=1000
Like
/dev/null, /dev/zero acts as a source and sink for data. All writes to
/dev/zero succeed with no other effects (the same as for /dev/null,
although /dev/null is the more commonly used data sink); all reads on
/dev/zero return as many NULs as characters requested.
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