语法: grep [options] pattern [files]

我如何才能找到文件中匹配指定关键字的所有行?
在这个例子中, grep在/etc/passwd文件中查找包含文件John并显示所有的匹配行.

# grep John /etc/passwd
jsmith:x:1082:1082:John Smith:/home/jsmith:/bin/bash
jdoe:x:1083:1083:John Doe:/home/jdoe:/bin/bash

选项 -v, 显示除匹配行外的所有行. 在下面的例子中, 显示/etc/passwd文件中未匹配John的所有记录行.

注释: 在/etc/passwd中有一些行是未包含单词John. 下面仅显示输出的第一行.

# grep -v John /etc/passwd
jbourne:x:1084:1084:Jason Bourne:/home/jbourne:/bin/bash

计算特定文件中文件模式的匹配行数

在下面的例子中, 显示/etc/passwd文件里包含John文本的总行数.

# grep -c John /etc/passwd
2

你也可以通过-cv选项统计未匹配指定模式的总行数.

# grep -cv John /etc/passwd
39

查找文本忽略大小写
通过-i选项(忽略大小写), 将在搜索过程中忽略大小写.

# grep -i john /etc/passwd
jsmith:x:1082:1082:John Smith:/home/jsmith:/bin/bash
jdoe:x:1083:1083:John Doe:/home/jdoe:/bin/bash

在所有子目录中搜索匹配项
使用-r选项(递归)实现. 在下面的例子中, 在/home/users目录下的所有子目录中忽略大小写搜索文本”John”.

显示格式为”文件名: 匹配行”. 你也可以通过-l选项, 仅显示匹配的文件名.

# grep -ri john /home/users
/home/users/subdir1/letter.txt:John, Thanks for your contribution.
/home/users/name_list.txt:John Smith
/home/users/name_list.txt:John Doe
# grep -ril john /root
/home/users/subdir1/letter.txt
/home/users/name_list.txt

1. 从本地主机登录远程主机

localhost$ ssh -l jsmith remotehost

2. 在远程主机上输入转义符 ~ 和 s . 将会显示许多关于当前连接SSH的有用的统计信息.

remotehost$ [注释:  当你输入~s 命令时, 该命令并没有显示在屏幕上.]
remote host: remotehost
local host: localhost
remote version: SSH-1.99-OpenSSH_3.9p1
local version: SSH-2.0-3.2.9.1 SSH Secure Shell (non-commercial)
compressed bytes in: 1506
uncompressed bytes in: 1622
compressed bytes out: 4997
uncompressed bytes out: 5118
packets in: 15
packets out: 24
rekeys: 0
Algorithms:
Chosen key exchange algorithm: diffie-hellman-group1-sha1
Chosen host key algorithm: ssh-dss
Common host key algorithms: ssh-dss,ssh-rsa
Algorithms client to server:
Cipher: aes128-cbc
MAC: hmac-sha1
Compression: zlib
Algorithms server to client:
Cipher: aes128-cbc
MAC: hmac-sha1
Compression: zlib
localhost$

更多SSH信息
配置基于SSH密钥的身份验证, 请参考openSSH和SSH2的教程.

1. 从本地登录远程主机:

localhost$ ssh -l jsmith remotehost

2. 现在已连接到远程主机:

remotehost$

3. 临时返回本地, 键入转义符 ~ 和 Control-Z.
当键入~后并不会马上在屏幕上显示, 直到输入 <Control-Z> 和 回车.

remotehost$ ~^Z
[1]+ Stopped ssh -l jsmith remotehost
localhost$

4. 现在返回本地主机, SSH远程主机会话做为一个典型的UNIX进程在后台运行:

localhost$ jobs
[1]+ Stopped ssh -l jsmith remotehost

5. 切换回SSH远程主机会话(不需要再次输入密码).

localhost$ fg %1
ssh -l jsmith remotehost
remotehost$

localhost$ ssh -l jsmith remotehost.example.com
warning: Connecting to remotehost.example.com failed: No address associated to the name

locaclhost$ ssh -v -l jsmith remotehost.example.com
debug: SshConfig/sshconfig.c:2838/ssh2_parse_config_ext: Metaconfig parsing stopped at line 3.
debug: SshConfig/sshconfig.c:637/ssh_config_set_param_verbose: Setting variable ‘VerboseMode’ to ‘FALSE’.
debug: SshConfig/sshconfig.c:3130/ssh_config_read_file_ext: Read 17 params from config file.
debug: Ssh2/ssh2.c:1707/main: User config file not found, using defaults. (Looked for ‘/home/jsmith/.ssh2/ssh2_config’)
debug: Connecting to remotehost.example.com, port 22… (SOCKS not used)
warning: Connecting to remotehost.example.com failed: No address associated to the name

localhost$ ssh -l jsmith remotehost.example.com
Host key not found from database.
Key fingerprint:
xabie-dezbc-manud-bartd-satsy-limit-nexiu-jambl-title-jarde-
tuxum
You can get a public key’s fingerprint by running
% ssh-keygen -F publickey.pub
on the keyfile.
Are you sure you want to continue connecting (yes/no)? Yes
Host key saved to
/home/jsmith/.ssh2/hostkeys/key_22_remotehost.example.com.pub
host key for remotehost.example.com, accepted by jsmith Mon
May 26 2008 16:06:50 -0700
jsmith@remotehost.example.com password:
remotehost.example.com$

当你第二次通过本机登录远程主机时,  将作为已知主机的SSH客户端, 只需输入密码.

localhost$ ssh -l jsmith remotehost.example.com
jsmith@remotehost.example.com password: 
remotehost.example.com$

出于某些原因, 在你第一次登录远程主机后, 远程主机更改了密钥, 你可能会收到如下所示的一条警告消息.

这可能是因为如下一些原因:
系统管理员在远程主机上升级/重新安装SSH服务
有人正在进行恶意活动等等

在上述消息中选择”Yes”前, 最好联系你的系统管理员确认并核实你的主机密钥是否正确.

localhost$ ssh -l jsmith remotehost.example.com
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@       WARNING: HOST IDENTIFICATION HAS CHANGED!         @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the host key has just been changed.
Please contact your system administrator.
Add correct host key to
“/home/jsmith/.ssh2/hostkeys/key_22_remotehost.example.com.pu
b”
to get rid of this message.
Received server key’s fingerprint:
xabie-dezbc-manud-bartd-satsy-limit-nexiu-jambl-title-arde-
tuxum
You can get a public key’s fingerprint by running
% ssh-keygen -F publickey.pub
on the keyfile.
Agent forwarding is disabled to avoid attacks by corrupted
servers.
Are you sure you want to continue connecting (yes/no)? yes
Do you want to change the host key on disk (yes/no)? yes
Agent forwarding re-enabled.
Host key saved to
/home/jsmith/.ssh2/hostkeys/key_22_remotehost.example.com.pub
host key for remotehost.example.com, accepted by jsmith Mon
May 26 2008 16:17:31 -0700
jsmith @remotehost.example.com’s password: 
remotehost$

下面例子表明一个使用OpenSSH的特定系统:

$ ssh -V
OpenSSH_3.9p1, OpenSSL 0.9.7a Feb 19 2003

下面例子表明一个使用SSH2的特定系统:

$ ssh -V
ssh: SSH Secure Shell 3.2.9.1 (non-commercial version) on i686-pc-linux-gnu

$ date
Thu Jan 1 08:30:07 PST 2009

$ date –date=’3 seconds’
Thu Jan 1 08:30:12 PST 2009

$ date –date=’4 hours’
Thu Jan 1 12:30:17 PST 2009

$ date –date=’tomorrow’
Fri Jan 2 08:30:25 PST 2009

$ date –date=”1 day”
Fri Jan 2 08:30:31 PST 2009

$ date –date=”1 days”
Fri Jan 2 08:30:38 PST 2009

$ date –date=”2 days”
Sat Jan 3 08:30:43 PST 2009

$ date –date=’1 month’
Sun Feb 1 08:30:48 PST 2009

$ date –date=’1 week’
Thu Jan 8 08:30:53 PST 2009

$ date –date=”2 months”
Sun Mar 1 08:30:58 PST 2009

$ date –date=”2 years”
Sat Jan 1 08:31:03 PST 2011

$ date –date=”next day”
Fri Jan 2 08:31:10 PST 2009

$ date –date=”-1 days ago”
Fri Jan 2 08:31:15 PST 2009

$ date –date=”this Wednesday”
Wed Jan 7 00:00:00 PST 2009

$ date –date=’3 seconds ago’
Thu Jan 1 08:27:00 PST 2009

$ date –date=”1 day ago”
Wed Dec 31 08:27:13 PST 2008

$ date –date=”1 days ago”
Wed Dec 31 08:27:18 PST 2008

$ date –date=”1 month ago”
Mon Dec 1 08:27:23 PST 2008

$ date –date=”1 year ago”
Tue Jan 1 08:27:28 PST 2008

$ date –date=”yesterday”
Wed Dec 31 08:27:34 PST 2008

$ date –date=”10 months 2 day ago”
Thu Feb 28 08:27:41 PST 2008

$ date
Thu Jan 1 08:19:23 PST 2009

$ date –date=”now”
Thu Jan 1 08:20:05 PST 2009

$ date –date=”today”
Thu Jan 1 08:20:12 PST 2009

$ date –date=’1970-01-01 00:00:01 UTC +5 hours’ +%s
18001

$ date ‘+Current Date: %m/%d/%y%nCurrent Time:%H:%M:%S’
Current Date: 01/01/09
Current Time:08:21:41

$ date +”%d-%m-%Y”
01-01-2009

$ date +”%d/%m/%Y”
01/01/2009

$ date +”%A,%B %d %Y”
Thursday,January 01 2009

date命令参数格式选项:

o %D    日期 (mm/dd/yy)
o %d    月中的日期 (01..31)
o %m    月份 (01..12)
o %y    年份的后两位数 (00..99)
o %a    星期名称缩写 (Sun..Sat)
o %A    星期名称全称 (Sunday..Saturday)
o %b    月份名称缩写 (Jan..Dec)
o %B    月份名称全称 (January..December)
o %H    24小时制 (00..23)
o %I    12小时制 (01..12)
o %Y    年份 (1970…)

基于系统时间设置硬件的日期和时间:

# hwclock –systohc
# hwclock –systohc –utc

使用没带参数的hwclock命令显示当然硬件时间:

# hwclock

检查时钟文件检验系统是否设置为UTC:

# cat /etc/sysconfig/clock
ZONE=”America/Los_Angeles”
UTC=false
ARC=false