Python Full Stack road Day9

Tag: IDT Test successfully represents the status of LIS sys file one

first edited September 25, 2017 22:43:40

Summary
I. Shell's basic syntax-variables
Two. Shell's basic syntax-operator
Three. Process Control
Homework
Summary today

Summary

Citation: Mr. Haifeng

1. Basic syntax of the shell
2. Process Control, script transfer

I. Shell's basic syntax-variables

1. Naming rules
   1. Start with a letter
   2. Connect words with an underscore or an underscore
   3. The same type is distinguished by numbers
   4. For file best plus extension
2. System variables
   • Set and env differences
   • Set: Show All variables
   • ENV: System Variables
3. Assigning values to variables
   • unset VARNAME: Deleting variables
4. Common system Variables
   • PATH
   • Pwd
   • Lang
   • HOME
   • Histsize: Number of history log lines
   • PS1: Storing user information
   • Ifs
   • Export: Defining global variables
5. Define the bounds of a variable name
   [Email protected] ~]# rest_mem=20
   [Email protected] ~]# echo ${rest_mem}%
   20%
6. Data type

Two. Shell's basic syntax-operator

2. Arithmetic operators
   • +
   • -
   • *
   • /
   • %
4. Relational operations
   • <
   • >
   • <=
   • >=
   • ==
   • !=
   • &&
   • ||
     • Above with (())
   • Test command related, [] can achieve the same effect
6. Assignment operators
   • =
   • +=
   • *=
   • /=
   • %=
   • [Email protected] ~]# ((x%=3))
     [Email protected] ~]# echo $x
8. All the calculators in the shell
   • $[]
   • (())
   • $(())
   • Expr
   • Floating-point arithmetic BC Software
     • Yum Install Bc-y
     • Echo ' SCALE=2;1/3 ' |bc-l (retains two bits, 1 divided by 3 operations)
9. Test action
   1. After the
   2. command executes, it returns to a system variable ? & #x5982; & #x679C; Style= "font-size:100%; Display:inline-block; Position:relative "> ? A value of 0 indicates that the command executed successfully or failed
   4. Testing command test [] [[]] (())
      1. Test file status
         • -D Directory
         • -E
         • -H Link File
         • -S file length > 0, non-empty
         • -F Normal File
         • -W Writable
         • -R Readable
         • -X Executable
         • -L Symbolic connection
         • -u file has suid bit settings
         • -B Block File
      2. String test
         • = Two strings equal
         • ! = two strings are not equal
         • -Z Empty string
         • -N Non-empty string
      3. Test values
         • -eq equals
         • -ne Not equal to
         • -GT Greater than
         • -lt less than
         • -ge greater than or equal to
         • -le less than or equal to
      4. Expand Test Symbols

Three. Process Control

1. The IF statement for Process Control

#!/bin/bashvar=‘/etc/init.d‘#var=‘/dev/sda‘if [ -d $var ]    then        echo "$var is directory"elif [ -b $var ]    then        echo "$var is block"elif [ -f $var ]    then        echo "$var is regular file"else        echo ‘unknow‘fi

• Passing parameters to a script

#test.shecho $0echo $1echo $2echo $3echo ${11}echo ‘$$‘ $$echo ‘$*‘ $*echo ‘[email protected]‘ [email protected]echo ‘$#‘ $#echo ‘$?‘ $?‘‘‘测试：python test.sh 1 2 3 4 5 6 7 8 9 10 11输出结果：./test.sh    211$$ 14312$* 1 2 3 4 5 6 7 8 9 10 11[email protected] 1 2 3 4 5 6 7 8 9 10 11$# 11$? 0‘‘‘

* $0 为运行的文件名* $$ 为进程pid* $* 为输入的所有的参数* [email protected] 同$** $# 输入参数个数* $? 上一条命令是否执行成功

• Modify the script so that it can receive the arguments from the caller

[[email protected] ~]# cat test_file.sh#!/bin/bashif [ -d $1 ]    then        echo "$1 is directory"elif [ -b $1 ]    then        echo "$1 is block"elif [ -f $1 ]    then        echo "$1 is regular file"else        echo ‘unknown‘fi[[email protected] ~]# ./test_file.sh /etc/passwd/etc/passwd is regular file

• Detects if Nginx is started, and if not, starts it

#! /bin/bashps aux|grep nginx|grep -v grepif [ $? -eq 1 ]    then        systemctl start nginxfi

Homework

Summary today

Python Full Stack road Day9