sed:
syntax: sed [options] 'command' [files]
sed [options] -e 'conmand1' -e 'command2' ......[files]
sed [options] -f script [files]
每次读取一行
frequently options
-e cmd[command abbreviate]
the next argument is a command.this is not need for a single command, but is required for all commands when multiple commands was specified
-f file the next argument is a script
-g treat all substitution as global
frequence used parameter
d delete lines
y translate characters. similar to the tr command.(针对每一个字符)
s make stitution. the syntax is s/pattern/replacement/[flags]（把pattern看作一个整体）
the following flags can be specified for the s command:
g replace all instance of pattern, not just the first
n replace nth instance of pattern, the default is 1
p print the line if a successful substitution is done. generally used with the -n command-line option
w file print the line to file if a successful is done
for example:
delete lines 3 through 5 of file
sed '3,5d' file1
delete the lines of file1 that contain a # at the begin of the line:
$sed '/^#/d' file1
delete any line that don't contain #keepme:
sed '/#keepme/!d' file1
delete lines containing only whitespace(spaces or tabs). in the
example, tab means the single tab character and is precede by a single
space
sed '/^[ tab]*$/d' file1
subtitute a single space for any number of spaces wherever they occur on the line:
sed 's/ */ /g' file1
substitue def for abc from line 11 to 20, wherever it occurs on the lines:(是将字符串abc替换，而不是每一个字母)
sed '11,20s/abc/def/g' file1
translate the characters a, b, c to the @ character from line 11 to 20, wherever they occur on the line:
sed '11,20y/abc/@@@/'
translate characters sed 'y/abc/xyz/' file1 every instance of a is replaced to x, b to y, c to z.
write the @ symbol for all empty line in file1
sed '/^$/@/g' file1
将所有的小数替换成&*，和appel替换成apple
sed -e s/[0-9]\.[0-9][0-9]/&*/g -e s/appel/apple/g
substitution all after brucket to blank(替换所有以'（'开头的为空)
$id|sed 's/(.*/ /'
use the command from the external file sedmds.replace the third and fourth double quotation marks with ( and ) on lines 1 through 10 in file1.make no change from 11 to the end of the file.script file sedmds contains:
1,10{
s/"/(/3
s/"/)/4}
the command is execute using the -f option
sed -f sedcmds file1
in the example, since the third double quote has been replace with (, it is no counted as a double quote by the second command. thus, the second command will operate on the fifth double quote character in the original file1. if the input line starts out with:" " " " " and the stitution consequence is " " ( " )
when stitution characters is error. above instance is ok.
假如文件files里含有如下的内容：
pintf "please input a file"
printf "I hava inputed file"
执行如下的命令
$sed 's/i/@/2/' files
输出结果如下：
pintf "please @nput a file"
printf "I hava @nputed file"
一些有用的正则表达式
/^$/ 空白行
/^.*$/ 一整行
/*/ 一个或多个空格
/<[^>]*>/ HTML（或XML）标记符
/[a-zA-z][a-zA-Z]*:[0-9a-zA-Z]*.*/ 有效的URL
/\$[0-9]*\.[0-9][0-9]/ 格式化的美元数
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