shell string processing

0. string of small knowledge

String may be composed of single quotes ' 'enclosed in double quotes may be " "enclosed in quotation marks may not, there is a difference between them:

1) a single quotes ' 'surrounded string:

• Any characters will be output as , in which a variable is invalid.
• String can not appear single quotation marks , even on single quote escape is not OK .

2) a double quotes " "surround string:

• If contains a variable, then that variable will be resolved (to get the value of the variable), rather than as it is output.
• String can appear in double quotes , as long as it escaped on the line .

3) is not a quoted string

• Appears in the string is not surrounded by quotes in the variable time to time will be resolved , and this double-quoted " "strings enclosed by the same.
• String can be no spaces , otherwise the space behind the other strings as variable or command parsing.

Get string length may be $ {# string_name}

1. String taken

1.1 taken from the specified start location

 

principle	The original string var=http://www.aaa.com/123.html	result
The first character to the left is indicated by 0, the right of the first character is represented by 0-1, the starting number is 1 ${string: start :length} start: length specified starting position and length, the length of the omitted word represents until the end of the string	$ echo out the { the var : 0 to : 5 }	http:
	$ echo out the { the var : 7 }	www.aaa.com/123.html
	$ echo out the { the var : 0 to - 7 : 3 }	23.
	$ echo out the { the var : 0 to - 7 }	23.html

1.2 taken from the specified character (substring) Start

principle	The original string var=http://www.aaa.com/123.html	result
# ## represents the start deleting from the left. A  # means to delete from the left to the first specified character; Two  # means to delete from the left to the last character specified.	the var $ {# echo out the * / }	/www.aaa.com/123.html
	the var $ ## {echo out the * / }	123.html
% %% indicates the start deleting from the right. A  % said the right to delete from the first specified character; Liangge  % said deleted from the left to the last character specified. Deleted includes the specified character itself.	the var% $ {echo out the / * }	http://www.aaa.com
	the var %% $ {echo out the / * }	http:
*It is a wildcard, an arbitrary length string representation If you do not ignore a character specifies the character left / right, then you can not write* * Means zero or more of any character,? Represents only one match any character, [...] which matches the characters in brackets, [! ..] in brackets represent the characters do not match.	echo ${var#http:/} the var% $ {echo out the 123html }	/www.aaa.com/123.html http://www.aaa.com

1.3 Summary of string interception

format	Explanation	For Li
${string: 0-start :length}	Starting on the right string string of start character, the interception of length characters to the right.	var=/home/wwwroot/ echo $var #result is /home/wwwroot/ echo ${var:5} #result is /wwwroot/ echo ${var: -5} #result is root/ echo ${var:(-5)} #result is root/ echo ${var:0-5} #result is root/ echo ${var:1-5} #result is oot/
${string: 0-start}	From the right string string of characters start capturing start until the end. Extracting from the right string starts, but must be used after the colon spaces or a number or entire num parentheses , such as $ {var: -2}, $ {var: 0-2} or $ {var: (- 2 )}.
${string: start :length}	From the left string string of start character, the interception of length characters to the right.	var="http://www.runoob.com/linux/linux-shell-variable.html" s1 = $ {var %% t *   } Results: h s2 = $ {var% t *     } Results: http://www.runoob.com/linux/linux-shell-variable.h s3 = $ {var %% *.   } Results: HTTP: // WWW s4=${var#*/}      结果：/www.runoob.com/linux/linux-shell-variable.html s5=${var##*/}    结果：linux-shell-variable.html
${string: start}	从 string 字符串的左边第 start 个字符开始截取，直到最后。
${string#*chars}	从 string 字符串第一次出现 *chars 的位置开始，截取 *chars 右边的所有字符。
${string##*chars}	从 string 字符串最后一次出现 *chars 的位置开始，截取 *chars 右边的所有字符。
${string%*chars}	从 string 字符串第一次出现 *chars 的位置开始，截取 *chars 左边的所有字符。
${string%%*chars}	从 string 字符串最后一次出现 *chars 的位置开始，截取 *chars 左边的所有字符。

1.4 按指定要求截取

ls -al | cut -d "." -f2  获取后缀名 

echo $test|cut -c1-8

2.字符串的拼接

	脚本	结果	注意点
拼接字符	$value1=home $value2=${value1}"=" echo $value2	home=	1.在 Shell 中不需要使用任何连接符，将两个字符串并排放在一起就能实现拼接 2.变量名要加{}，避免变量名与其他字符向混淆
拼接字符串	var0=test var1=43 echo ${var0}${var1}	test43

3.字符串的替换

语法：${变量/查找/替换值} 一个'/'表示替换第一个，'//'表示替换所有，当查找中出现了特殊字符"/"，需要转移成"\/"。

test='c:/windows/boot.ini'	脚本	结果
替换第一个/	echo ${test/\//\\}	c:\windows/boot.ini
替换所有/	echo ${test//\//\\}	c:\windows\boot.ini