05.Shell of the universe is a great diversion

If the expression contains special characters, the Shell will replace it. For example, using a variable in double quotes is a substitution, and an escape character is also a substitution.
As an example:

#!/bin/bash

a=10

Echo-e "The universe is $a \ n"

Operation Result: The universe is a big diversion .

here-e indicates the substitution of the escape character. If you do not use the-e option, the output will be as-is: the big move

The following escape characters can be used in echo:

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You can suppress escaping by using the-e option of the Echo command, which is not escaped by default, or by using the-N option to prevent the insertion of line breaks.

Command substitution

Command substitution means that the shell can execute commands first, save the output temporarily, and output it where appropriate.

Syntax for command substitution:

' Command '

Note that it is an anti-quote, not a single quote, which is below the ESC key.

In the following example, the command execution results are saved in a variable:

#!/bin/bash

Date= ' Date '
echo "Current date is: $DATE"

Users= ' who | Wc-l '
echo "Login user has $USERS"

up= ' date; Uptime '
echo "Time: $UP"

Operation Result:

The current date is: Mon June 00:28:39 PDT 2016 login users have 2 times: Mon June 00:28:39 PDT 00:28:39 up 5:29, 2 users, load average:0. 00, 0.00, 0.00

Variable substitution

The variable substitution form you can use:

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An example:

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05.Shell of the universe is a great diversion