Initial knowledge of shell scripts

#！ /bin/bash (the declaration of theLinux scripting environment is the interpreter, which is bash, under the bin directory in the root directory )

Definition and assignment of variables:

Format: Variable name = variable value ( No need to declare variable type )

A reference to a variable:

Format: $ variable name or ${variable name}

Content inside double quotes allows variable references and \ Escapes

Content within single quotes does not allow variable references and \ Escapes (no effect for variable references and escapes)

Inverse apostrophe ( key to the left of the keypad number 1 key ) or $ (): Replace with command output

Parameters used to set/record the system's operation ( environment variables ):

System assignment: USER, LOGNAME, HOME, SHELL ...

User action: PATH, LANG, CLASSPATH ....

Controlled by a system or script, not directly assigned:

Initial knowledge of shell scripts