Shell script string The difference between single and double quotes _linux shell

Basic knowledge of strings

Strings are the most commonly used data types in shell programming (except numbers and strings, and nothing else works), strings can be in single quotes, double quotes, or without quotes. The difference between single and double quotes is similar to PHP.

Single quotation mark

Copy Code code as follows:

Str= ' This is a string '

Single quote string limit:

• Any character in the single quotation mark is output as is, and the variable in the single quote string is invalid;
• Single quotes cannot appear in single quote strings (not after using escape characters for single quotes).

Double quotes

Copy Code code as follows:

Your_name= ' QINJX '
Str= "Hello, I know your are \" $your _name\ "! \ n "

Advantages of double quotes:

• Double quotes can have variables
• Escape characters can appear in double quotes

Common string-related methods

Stitching strings

Copy Code code as follows:

Your_name= "QINJX"
greeting= "Hello," $your _name "!"
greeting_1= "Hello, ${your_name}!"

echo $greeting $greeting _1

Get string length

Copy Code code as follows:

string= "ABCD"
echo ${#string} #输出 4

Extract substring

Copy Code code as follows:

String= "Alibaba is a great company"
Echo ${string:1:4} #输出liba

Find substring

Copy Code code as follows:

String= "Alibaba is a great company"
echo ' expr index ' $string ' is '

More string processing methods please refer to: http://www.jb51.net:81/article/50435.htm