Linux String and Digital字符串和数字

String definition

#Global variable define
str1=abc;
str2="abc";
str3='abc';
#local variable define
fn1() {
	local local_str1=abc;
	local local_str2="abc";
	local local_str3='abc';
}
function fn1 {
	local local_str1=abc;
	local local_str2="abc";
	local local_str3='abc';
}

Use String Variable

1. Normal use, return str

   • ${str}: same as $str.

   echo "$str1";
   echo "${str1}";
   echo $str1; 
   echo ${str1};
   #位置参数大于9的，一定要加花括号，例如第十个位置参数:
   ${11}
   

2. Return str OR defaultVal

   • ${str-defaultVal}: If str is undefined, return defaultVal.
   • ${str:-defaultVal}: If str is undefined or empty, return defaultVal.

   # str undefined
   echo ${str-defaultVal}; #output defaultVal
   echo ${str:-defaultVal}; #output defaultVal
   echo ${str}; # nothing
   # str defined
   str="abc";
   echo ${str-defaultVal}; #output abc
   echo ${str:-defaultVal}; #output abc
   echo ${str}; # abc
   # different(str is empty)
   str=;
   echo ${str-defaultVal}; #output ''(empty)
   echo ${str:-defaultVal}; # output defaultVal
   

3. Set and return defaultVal ,OR return str.(位置参数或特殊参数不能以这种方式赋值)

   • ${str=defaultVal}: If str is undefined, set str=defaultVal and return defaultVal.
   • ${str:=defaultVal}: If str is undefined or empty, set str=defaultVal and return defaultVal.

   # str undefined
   echo ${str=defaultVal}; #output defaultVal and set str=defaultVal
   echo ${str:=defaultVal}; #output defaultVal and set str=defaultVal
   echo ${str}; # output defaultVal
   #str defined
   str="abc";
   echo ${str=defaultVal}; # output abc.
   echo ${str:=defaultVal}; # output abc.
   echo ${str}; # output abc
   #different(str is empty)
   str=;
   echo ${str=defaultVal}; # output ''(empty)
   echo ${str:=defaultVal}; # output defaultVal.
   

4. Return newDefineVal OR empty

   • ${str+newDefinedVal}: If str is defined, return newDefinedVal,else return empty.
   • ${str:+notEmptyVal}: If str is defined and is not empty,return notEmptyVal.else return empty.

   # str undefined
   echo ${str+newDefineVal}; #output ''(empty)
   echo ${str:+newDefineVal}; #output ''(empty)
   #str defined
   str="abc";
   echo ${str+newDefinedVal}; # output newDefinedVal
   echo ${str:+newDefinedVal}; # output newDefinedVal
   #different(str is empty)
   str=;
   echo ${str+newDefinedVal};# output newDefinedVal
   echo ${str:+newDefinedVal};# output ''(empty)
   

5. Print error message OR str

   • ${str?ERR_MSG}: If str is undefined print ERR_MSG, else return str.
   • ${str:?ERR_MSG}: If str is undefined or empty, print ERR_MSG.else return str.

   #str undefined
   echo ${str?undefined}; #output "-bash: stsfdr: undefined"
   echo ${str:?undefineOrEmpty}; #output "-bash: stssr: undefineOrEmpty"
   #str defined
   str="abc";
   echo ${str?undefined}; #output abc
   echo ${str:?undefinedorEmpty}; # output abc
   # different (str is empty)
   str=;
   echo ${str?undefined}; #output ''(empty)
   echo ${str:?undefinedOrEmpty} # output "-bash: stssr: undefineOrEmpty"
   

6. Match prefix

   • ${!strPrefix*}：Matches all variables starting with strPrefix.
   • ${!strPrefix@}: The same as above.

   #str undefined
   echo ${!str*}; # output ''(empty)
   #str defined
   str=abc
   str1=abc1;
   str2=abk2;
   str3=abe3;
   str4=abd4;
   e${!str*}; # output 'str str1 str2 str3 str4'
   

String operation（length, substr, replace）

1. Length.

   • ${#str}：Length of string.

   #str undefined
   echo ${#str}; #output 0
   #str defined
   str="abcdefg";
   echo ${#str}; #output 7
   

2. Substring.

   • ${str:position}：substring start at position.
   • ${str:position:length}：substring of length start at position.
   • ${str#substr}：Remove the shortest matching substr at the beginning of str
   • ${str##substr}：Remove the longest matching substr at the beginning of str.
   • ${str%substr}：Remove the shortest matching substr at the end of str .
   • ${str%%substr}：Remove the longest matching substr at the end of str.

   attention:

   • substr support "*" wildcard.
   • shortest and longest is working at "*" wildcard.

   # If str undefined, All of them return ''(empty)
   #str defined
   str="aabbcckkaabbkk";
   echo ${str:0}; #output the whole str, aabbcckkaabbkk
   echo ${str:3}; #output bcckkaabbkk
   echo ${str:3:2}; #output bc
   echo ${str#aab}; # output bcckkaabbkk
   echo ${str#*b};  # output bcckkaabbkk
   echo ${str##aab}; # output bcckkaabbkk
   echo ${str##*b}; #output kk
   echo ${str%bkk}; #output aabbcckkaab
   echo ${str%b*};  #output aabbcckkaab
   echo ${str%%bkk}; #output aabbcckkaab
   echo ${str%%b*};  #output aa
   

3. Replace

   • ${str/oldstr/newstr}：replace oldstr once with newstr.
   • ${str//oldstr/newstr}：replace all oldstr with newstr.
   • ${str/#oldstr/newstr}：replace oldstr with newstr at the beginning.
   • ${str/%oldstr/newstr}：replace oldstr with newstr at the end.

   attention:

   • oldstr support "*" wildcard.

   str1="aabbddaakkdd";
   ##replace
   echo "${str1/aa/111}"; //replace：111bbddaakkdd
   echo "${str1//aa/111}"; //replaceAll: 111bbdd111kkdd
   echo "${str1/#aa/111}"; //replace begin: 111bbddaakkdd
   echo "${str1/#bb/111}"; //replace begin(没匹配上): aabbddaakkdd
   echo "${str1/%dd/111}"; //replace end：aabbddaakk111
   echo "${str1/%aa/111}"; //replace end(没匹配上)：aabbddaakkdd
   

key words: linux字符串，字符串定义，字符串替换，字符串截取。

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