Linux single quotes, double quotes, and reverse quotes

Single quotes

Purpose: To prevent text conversion. Except for the single quotation marks, all words in the single quotation marks are output as is.

1. [root @ jszwl161 sp49ep9] # echo '$ *> <! '

$ *> <!

2. [root @ jszwl161 sp49ep9] # echo 'she is crying: "Help "'

She is crying: "Help"

3. [root @ jszwl161 sp49ep9] # echo '\\\\'

\\\\

4. [root @ jszwl161 sp49ep9] # echo 'hah'test''

Hah test # skipped all'

5. [root @ jszwl161 sp49ep9] # echo 'Today is 'date''

Today is 'date' # The function cannot be implemented here.

Double quotation marks

Purpose: To include text or function segments, except for functions in the backquotes, variables starting with $, and characters in the backticks are directly output.

1. [root @ jszwl161 sp49ep9] # echo "Today is 'date '"

Today is Fri Jul 4 08:03:34 GMT 2008

2. [root @ jszwl161 sp49ep9] # echo "Today is 'date '"

Today is 'date'

3. [root @ jszwl161 sp49ep9] # echo "\\\\"

\\

4. [root @ jszwl161 sp49ep9] # echo "test" test ""

Test test

Reverse quotation marks

The objective is to keep Function Conversion within double quotes, but it does not work in single quotes.

1. [root @ jszwl161 sp49ep9] # echo "Today is 'date '"

Today is Fri Jul 4 08:03:34 GMT 2008 # convert the function date.

2. [root @ jszwl161 sp49ep9] # echo 'Today is 'date''

Today is 'date' # It does not work in single quotes.

 

 

 

Single quotes

The content enclosed by single quotes is considered as a single string. The $ symbol representing the variable in quotation marks does not work. That is to say, it is treated as a general symbol to prevent replacement of any variable.

Double quotation marks
The content enclosed by double quotation marks is considered as a single string. It prevents wildcard extension, but allows variable extension. This is different from how a single reference is processed.

Reverse quotation marks
The preceding single double quotes enclose strings. What if the string is a command column? The answer is no execution. To deal with this situation, we must use reverse single quotes.
Fdv = 'date + % F' echo "today $ fdv"

The date + % F in the inverted quotation marks is considered as an instruction, and the execution result is included in the fdv variable.

Address: http://kmoving.blog.163.com/blog/static/205049197201242211111682/