Linux single quotes, double quotes, anti-quotes

Single quotation marks
Purpose: In order to protect the text from being converted. That is, except for the single quote, all the text inside the single quotation marks is output as is.
1. [[email protected] sp49ep9]# echo ' $*><! '
$*><!
2. [[email protected] sp49ep9]# echo ' She's crying: ' Help '
She is crying: "Help"
3. [[Email protected] sp49ep9]# echo ' \\\\ '
\\\\
4. [[Email protected] sp49ep9]# echo ' hah ' test '
Hah Test #略去了所有 '
5. [[Email protected] sp49ep9]# echo ' Today is ' date '
Today is ' Date ' #反引号在此无法实现函数功能.

double quotes
Span style= "font-family: ' Microsoft Jacob Black ', Sans-serif;" Purpose: To include text or function segments. In addition to itself, the function inside the counter-quote, the variable starting with $ and the \ Start inverse of the character, the rest is the direct output.
1. [[email protected] sp49ep9]# echo "Today is ' Date '"
    today is Fri jul    4 08:03:34 GMT
2. [[email protected] sp49ep9]# echo "Today is ' Date '"
    today is ' Date '
3. [[email protected] sp49ep9]# echo "\\\\"
    \\
4. [[email protected] sp49ep9]# echo "test" test ""
    test test

Anti-Quote
The purpose is to keep the function transformation within the double quotation marks. But it has no effect in single quotation marks.
1. [[email protected] sp49ep9]# echo "Today is ' Date '"
Today is Fri Jul 4 08:03:34 GMT2008 #将函数date转换.
2. [[email protected] sp49ep9]# echo ' Today is ' date '
Today is ' Date ' #在单引号内无作用.

Single quotation marks

The enclosed quotation marks are treated as a single string. The $ sign that represents the variable within the quotation marks does not work, that is, he is treated as a general symbol and prevents any variable substitution.
Double quotes
The content enclosed in double quotes is treated as a single string. It prevents wildcard expansion, but allows variable expansion. This is different from the way a single argument is handled.
Anti-Quote
In the preceding single double quotation mark, enclose the string, but what if the string is a list of command columns? The answer is no execution. To deal with this situation, we have to use anti-single quotes to do it.
fdv= ' Date +%f ' echo "Today $FDV"
The date +%f in the inverted quotation marks is treated as an instruction, and the result of execution is taken into the FDV variable.

This article is from the "Itlang_jansion_goktech" blog, make sure to keep this source http://wangdy.blog.51cto.com/3845563/1570637

Linux single quotes, double quotes, anti-quotes