linux命令之md5sum
1.md5sum介绍
linux命令md5sum是用来计算和校验文件的MD5值。
另外：
md5sum是用来校验文件内容，与文件名是否相同无关
md5sum校验文件时，逐位校验，如果文件越大，校验所需时间就越长
2.md5sum用法
md5sum 参数 filename
|----------|-----------------------------|
| 参数 | 说明 |
| -b | 以二进制模式读入文件内容 |
| -t | 以文本模式读入文件内容 |
| -c | 从指定文件中读取 MD5 校验和，并进行校验 |
| --status | 不生成争取/错误提示信息，通过命令返回值来判断 |
[md5sum参数]
3.实例
3.1.查看md5sum帮助信息
命令：
md5sum --help
[root@rhel77 ~]# md5sum --help
Usage: md5sum [OPTION]... [FILE]...
Print or check MD5 (128-bit) checksums.
With no FILE, or when FILE is -, read standard input.
-b, --binary read in binary mode
-c, --check read MD5 sums from the FILEs and check them
--tag create a BSD-style checksum
-t, --text read in text mode (default)
Note: There is no difference between binary and text mode option on GNU system.
The following four options are useful only when verifying checksums:
--quiet don't print OK for each successfully verified file
--status don't output anything, status code shows success
--strict exit non-zero for improperly formatted checksum lines
-w, --warn warn about improperly formatted checksum lines
--help display this help and exit
--version output version information and exit
The sums are computed as described in RFC 1321. When checking, the input
should be a former output of this program. The default mode is to print
a line with checksum, a character indicating input mode ('*' for binary,
space for text), and name for each FILE.
GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
For complete documentation, run: info coreutils 'md5sum invocation'
[root@rhel77 ~]# 3.2.检查文件md5值
命令：
md5sum -t ztj.txt
OR
md5sum -b ztj.txt
root@rhel77 ~]# md5sum -t ztj.txt
cfc12d1432a7b067566080122b1c4f85 ztj.txt
[root@rhel77 ~]# md5sum -b ztj.txt
cfc12d1432a7b067566080122b1c4f85 *ztj.txt
[root@rhel77 ~]# 3.3.检查文件md5值，与文件无关
命令：
\cp ztj.txt ztj.txt.bak
md5sum ztj.txt
md5sum ztj.txt.bak
root@rhel77 ~]# \cp ztj.txt ztj.txt.bak
[root@rhel77 ~]# md5sum ztj.txt
cfc12d1432a7b067566080122b1c4f85 ztj.txt
[root@rhel77 ~]# md5sum ztj.txt.bak
cfc12d1432a7b067566080122b1c4f85 ztj.txt.bak
[root@rhel77 ~]# 3.4.从指定文件中读取MD5校验和，并进行校验
命令：
md5sum ztj.txt >> md5sum.txt
md5sum -c md5sum.txt
[root@rhel77 ~]# md5sum ztj.txt >> md5sum.txt
[root@rhel77 ~]#
[root@rhel77 ~]# md5sum -c md5sum.txt
ztj.txt: OK
[root@rhel77 ~]# 3.5.从指定文件中读取MD5校验和，并不显示校验信息，以命令返回值来判断
备注：
如果校验一致返回0，不一致返回1
命令：
md5sum -c --status md5sum.txt
echo $?
[root@rhel77 ~]# md5sum -c --status md5sum.txt
[root@rhel77 ~]# echo $?
0
[root@rhel77 ~]# OR
命令：
echo 111 >>ztj.txt
md5sum -c --status md5sum.txt
echo $?
[root@rhel77 ~]# echo 111 >>ztj.txt
[root@rhel77 ~]#
[root@rhel77 ~]# md5sum -c --status md5sum.txt
[root@rhel77 ~]# echo $?
1
[root@rhel77 ~]#