1. Shell variables
1) The basic format of defining variables
Variable name = value
Note that there cannot be a space between the variable name and the equal sign, which may be different from the familiar programming languages such as JAVA and C. At the same time, the naming of variable names must follow the following rules:
the first character must be a letter (az, AZ).
There can be no spaces in between, you can use an underscore (_).
Punctuation marks cannot be used.
You cannot use keywords in bash (reserved keywords can be viewed with the help command).
Note that there cannot be a space between the variable name and the equal sign, which may be different from the familiar programming languages such as JAVA and C. At the same time, the naming of variable names must follow the following rules:
the first character must be a letter (az, AZ).
There can be no spaces in between, you can use an underscore (_).
Punctuation marks cannot be used.
You cannot use keywords in bash (reserved keywords can be viewed with the help command).
2) Use variables
Define a variable
variable name=value
There are two ways to get the value of the variable:
a) $variable name
b) ${variable name}
#!/bin/bash
a=10
echo $a
echo ${a}
variable name=value
There are two ways to get the value of the variable:
a) $variable name
b) ${variable name}
#!/bin/bash
a=10
echo $a
echo ${a}
3) Readable variables
The format of the readable variable:
readonly variable name
(Note: adding this keyword before the variable name indicates that the variable is read-only and immutable)
#!/bin/bash
a=10
echo $a
echo ${a}
readonly a
a=100
echo $a
readonly variable name
(Note: adding this keyword before the variable name indicates that the variable is read-only and immutable)
#!/bin/bash
a=10
echo $a
echo ${a}
readonly a
a=100
echo $a
Execute script error
[imix@localhost shell]$ ./lsSh.sh
10
10
./lsSh.sh: line 6: a: read-only variable
10
10
10
./lsSh.sh: line 6: a: read-only variable
10
4) delete variable
The format of deleting a variable:
unset variable name
(Note: add unset before the variable name, the variable is undefined after this sentence, the unset command cannot delete read-only variables)
#!/bin/bash
a=10
echo $a
echo ${ a}
#readonly a
unset a
echo $a (because the variable has been deleted, this sentence will output nothing)
unset variable name
(Note: add unset before the variable name, the variable is undefined after this sentence, the unset command cannot delete read-only variables)
#!/bin/bash
a=10
echo $a
echo ${ a}
#readonly a
unset a
echo $a (because the variable has been deleted, this sentence will output nothing)
5) Commonly used variable types (numeric, string, array, environment variables)