Shell detailed introduction and programming (ON)

• Shell Introduction

The shell is a programming language interpreter, which interprets commands entered from the keyboard, and also explains the sequence of commands stored in the script, which is a file containing a series of commands, and running a script is running each command in the file. You can use a shell script to execute multiple commands in a single request. Shell script execution: Shell interpreter will execute this script command fork+exec, in the exec call, the kernel will check the first line of the script (for example: #!/bin/bash) to find an interpreter to execute the script, and then load the interpreter, which interprets the execution script

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• Execution of the shell

You can directly chmod +x shell.sh to join the Execute command./shell.sh run, you can also directly bash shell.sh execute bash-x You can see the details of the execution, Bash-n shell.sh can check for syntax errors, spelling errors will not prompt.

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• Shell's variables

Shell variables are: variable amount, named memory space

The bash environment variables are as follows:

Local variables: current shell process;

Environment variables: The current shell process and its child processes;

Local variables: a function execution process;

Positional parameter variables: references to parameters passed to the script in the script, and arguments passed to the function in the function;

Special variables: $?, $*, [email protected], $#, $$

Local variable definition:

Name=value//Name: Variable name =: Assignment symbol =: assignment symbol Value: Values

Variable name: can only contain numbers, letters and underscores, and cannot start with a number;

Reference variable: ${name}, $name//local variable definition and use, only valid for the current shell, log off and re-login is invalidated, the shell defined before the child process is also invalidated

In the script reference: Weak reference: "", its internal variable reference will be replaced with the value of the variable, strong reference: ", the variable reference of its variables will keep the original character; Command reference: ' Commands ', ' $ ';

Declared as integral: Declare-i Name[=value] or let Name=value

Invalidation or cancellation of a variable: script execution completes automatic destruction: Shell process terminates; manual destroy: unset name

[Email protected] bin]# tao= "shaonian.blog.51cto.com" [[email protected] bin]# echo $tao//DECLARE variable taoshaonian.blog.51cto. Com[[email protected] bin]# bash [[email protected] bin]# echo $tao//Sub-process invalidation [[email protected] bin]# Set//view variable Bash=/bi N/bashbashopts=checkwinsize:cmdhist:expand_aliases:extquote:force_fignore:hostcomplete:interactive_comments: Progcomp:promptvars:sourcepath

environment variable Definition:

A bit like a local variable that is "exported"

Export Name[=value]

Declare-x Name[=value]

View all environment variables: env, PRINTENV, Expor

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Local variables: A shell script execution process that takes effect only during shell script execution and then fails.

Special variables: $?, $*, [email protected], $#, $$

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Shell detailed introduction and programming (ON)