sed 系列: 用正则表达式查找和替换

The `s’ command is probably the most important in `sed’ and has a lot of different options.

The `s’ command attempts to match the pattern space against the supplied REGEXP; if the match is successful, then that portion of the pattern space which was matched is replaced with REPLACEMENT.

Syntax:
#sed 'ADDRESSs/REGEXP/REPLACEMENT/FLAGS' filename
#sed 'PATTERNs/REGEXP/REPLACEMENT/FLAGS' filename

s is substitute command
/ is a delimiter
REGEXP is regular expression to match
REPLACEMENT is a value to replace

LAGS can be any of the following

g Replace all the instance of REGEXP with REPLACEMENT
n Could be any number,replace nth instance of the REGEXP with REPLACEMENT.
p If substitution was made, then prints the new pattern space.
i match REGEXP in a case-insensitive manner.
w file If substitution was made, write out the result to the given file.
We can use different delimiters ( one of @ % ; : ) instead of /
建立测试文件
$ cat thegeekstuff.txt
# Instruction Guides
1. Linux Sysadmin, Linux Scripting etc.
2. Databases - Oracle, mySQL etc.
3. Security (Firewall, Network, Online Security etc)
4. Storage in Linux
5. Productivity (Too many technologies to explore, not much time available)
#  Additional FAQS
6. Windows- Sysadmin, reboot etc.

例子1：用Linux-Unix替换Linux
$ sed 's/Linux/Linux-Unix/' thegeekstuff.txt
# Instruction Guides
1. Linux-Unix Sysadmin, Linux Scripting etc.
2. Databases - Oracle, mySQL etc.
3. Security (Firewall, Network, Online Security etc)
4. Storage in Linux-Unix
5. Productivity (Too many technologies to explore, not much time available)
#  Additional FAQS
6. Windows- Sysadmin, reboot etc.

例子2：用s//g替换所有
$ sed 's/Linux/Linux-Unix/g' thegeekstuff.txt
# Instruction Guides
1. Linux-Unix Sysadmin, Linux-Unix Scripting etc.
2. Databases - Oracle, mySQL etc.
3. Security (Firewall, Network, Online Security etc)
4. Storage in Linux-Unix
5. Productivity (Too many technologies to explore, not much time available)
#  Additional FAQS
6. Windows- Sysadmin, reboot etc.

例子3：用s//2只替换第二个单词
$ sed 's/Linux/Linux-Unix/2' thegeekstuff.txt
# Instruction Guides
1. Linux Sysadmin, Linux-Unix Scripting etc.
2. Databases - Oracle, mySQL etc.
3. Security (Firewall, Network, Online Security etc)
4. Storage in Linux
5. Productivity (Too many technologies to explore, not much time available)
#  Additional FAQS
6. Windows- Sysadmin, reboot etc.

例子4：用s//gpw替换所有单词并打印和写入文件
$ sed -n 's/Linux/Linux-Unix/gpw output' thegeekstuff.txt
1. Linux-Unix Sysadmin, Linux-Unix Scripting etc.
4. Storage in Linux-Unix
$ cat output
1. Linux-Unix Sysadmin, Linux-Unix Scripting etc.
4. Storage in Linux-Unix

例子5：模式匹配替换
$ sed '/\-/s/\-.*//g' thegeekstuff.txt
# Instruction Guides
1. Linux Sysadmin, Linux Scripting etc.
2. Databases
3. Security (Firewall, Network, Online Security etc)
4. Storage in Linux
5. Productivity (Too many technologies to explore, not much time available)
#  Additional FAQS
6. Windows

例子6：删除每行的最后几个字母
$ sed 's/...$//' thegeekstuff.txt
# Instruction Gui
1. Linux Sysadmin, Linux Scripting e
2. Databases - Oracle, mySQL e
3. Security (Firewall, Network, Online Security e
4. Storage in Li
5. Productivity (Too many technologies to explore, not much time availab
#  Additional F
6. Windows- Sysadmin, reboot e

例子7：删除所有注释行
$  sed -e 's/#.*//' thegeekstuff.txt

1. Linux Sysadmin, Linux Scripting etc.
2. Databases - Oracle, mySQL etc.
3. Security (Firewall, Network, Online Security etc)
4. Storage in Linux
5. Productivity (Too many technologies to explore, not much time available)

6. Windows- Sysadmin, reboot etc.

例子8：删除所有注释行和空行
$ sed -e 's/#.*//;/^$/d'  thegeekstuff.txt
1. Linux Sysadmin, Linux Scripting etc.
2. Databases - Oracle, mySQL etc.
3. Security (Firewall, Network, Online Security etc)
4. Storage in Linux
5. Productivity (Too many technologies to explore, not much time available)
6. Windows- Sysadmin, reboot etc.

例子9：Dos到unix格式转换
Copy the DOS file to Unix, you could find \r\n in the end of each line.

This example converts the DOS file format to Unix file format using sed command.

$sed 's/.$//' filename

例子10：移除html标签（有待商榷）
In this example, the regular expression given in the sed command matches the html tags and replaces with the empty.

$ sed -e 's/<[^>]*>//g'
This <b> is </b> an <i>example</i>.
This  is  an example.