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How to use Shell online tools, I believe that many inexperienced people do not know what to do, so this article summarizes the causes of the problem and solutions, through this article I hope you can solve this problem.

Shell learning

Shell is a program written in C language, which is a bridge for users to use Linux. Shell is both a command language and a programming language.

Shell is an application that provides an interface through which users access the services of the operating system kernel

Shell online tool

Shell variable variable definition

The dollar sign is not required for the variable name (the dollar sign is more necessary for the use of the $variable), and the ``symbol is used to obtain the system variable.

MyName= "www.baodu.com" BAK_DIR=/usr/local/tomcat/webapps_bak/ `date +% Y% m% d`pid = `ps-ef | grep tomcat | grep "jdk" | awk-F''{print $2}'`

Note:

There can be no spaces between variables and between variables and equal signs.

Variable naming can only use English characters, numbers and underscores, and the first character cannot start with a number

Variables cannot use punctuation and special characters

Variables cannot use special keywords such as: bash shell

Variable use

The use of variables requires attention to [local variables] and [global variables]. Variables in shell can be local and global components.

The curly braces {} of the MyName= "www.baodu.com" echo $MyName echo ${MyName} # variable can be added or not, to help the interpreter identify the boundary of the variable #! / bin/bashfor salary in 1000 5000 5000 10000 Do echo "My salary is ${salary} yuan" done# variable redefines MyName= "www.baodu.com" echo ${MyName} MyName= "www.sogo.com" echo ${MyName} # read-only variable, need to add readonly keyword MyName= "www.baodu.com" echo ${MyName} readonly MyName# to delete variable, need to add unset keyword, cannot use #! / bin/bashMyName= "www.baodu.com" unset MyNameecho ${MyName} again after deletion

Shell string

The most common data type of a string, a string can be single quotation marks, double quotation marks (double quotation marks can appear escape characters), or should not be quoted.

#! / bin/bashMyName='www.baodu.com'str= "Hello, I know you are\" ${MyName}\ "!" echo ${str}

Get string length

#! / bin/bashMyName= "www.baodu.com" echo ${# MyName} get the use of the array #! / bin/bashMyName= "www.baodu.com" echo ${MyName:4:5} after intercepting the fifth character

The definition of an array can be separated by a [space] or [carriage return] symbol. Note that the subscript of the array starts with 0.

#! / bin/bash# define the array array_name= (Bananaappleorange) # or define the array array_name1= (Bananaappleorange) # define the value of the array array_name [0] = Bananaarray_name [1] = applearray_ name [n] = orange# use the array echo ${array_name [0]} echo ${array_name [1]} echo ${array_name [2]} echo ${array_ name [n]} # to get the number of array elements echo ${ # array_name [*]} echo ${# array_name [@]} # get the length of the array element echo ${# array_name [1]}

Use of comments

# single-line comment # Multi-line comment, EOF can also be other symbols:

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