Shell basic Syntax (i)

Composition + Execution

• Need to add #! at the beginning /bin/bash

• Lines that begin with # are interpreted as explanatory notes

• The name of the script ends with. SH and is used to differentiate between this is a shell script

• There are two methods of executing

  chmod +x 1.sh;./1.sh

  Bash 1.sh

• View the script execution process

  Bash-x 1.sh

• To see if the script is syntactically incorrect

  Bash-n 1.sh

Date command syntax

# date      //Simple Display current date 2017  09 month  12 Day   Tuesday  21:26:09  cst[[email protected] ~]# date +%y   //  simple four-digit    "year" 2017[[ email protected] ~]# date +%y   //  two digits      "year" 17[[ email protected] ~]# date +%m   // minute  "Minutes" 32[[email  protected] ~]# date +%m   // month     "Month" 09[[email  protected] ~]# date +%S   // Second    "Seconds" 21[[email  protected] ~]# date +%H   // Hour      "Hours" 21 [[email protected] ~]# date +%d   // date       "Date" 12[[email protected] ~]# date +%d   //   installation how to output in English format      "Month Day" 09/12/17[[email protected] ~]# date +%y%m%d       //  four-digit     "Month Day" 20170912[[email protected] ~]# date +%y%m%d        //  Two digits     month Day 170912[[email protected] ~]# date +%f            //  Special format   "Month Day" 2017-09-12[[email  protected] ~]# date +%T              Special formats   "hours and Seconds" 21:40:22[[email protected] ~]# date +%h%m%s        //  Combo     "hours/minute" 214500[[email protected] ~]# date +%h: %m:%s     //  custom     "hours/Minutes" 21:45:07[[email protected] ~]#  date +%w           // week      "Weeks" 2[[email protected] ~]# date +%w            //  weeks    37[[email protected] ~]# date -d  " -1  Day " +%F       //  Yesterday 2017-09-11[[email protected] ~]#  date -d  " -1 month"  +%F     //  last month 2017-08-12[[email  protected] ~]# date -d  " -1 years"  +%f     //   Last year 2016-09-12[[email protected] ~]# date -d  " -1 hour"  +%T       //  the past hour 21:00:33[[email protected] ~]# date +%s            //  How many seconds has it been since 1970?     timestamp      1505225506 conversion Timestamp at a point in time: (August 8, 2018 8:8 8 seconds Away 1970 years elapsed how many seconds) [[email protected] ~]#  date +%s -d  "2018-08-08 08:08:08 "1533686888 based on timestamp   get a specific time [[email protected] ~]# date -d @ 15,336,868,882,018 years  08 month  08   Wednesday  08:08:08 CST

Variables in the shell

• When using conditional statements, the variable if [$a-gt 1] is often used; Then ...; Fi

• Replace N=wc-l 1.txt with a variable when referencing the result of a command

• When writing and user interaction scripts, variables are also essential for read-p "Input a number:" N; Echo $n If you don't write this n, you can use $reply directly.

• Built-in variables $, $ $, $ ... $ $ represents the script itself, the first parameter, the $ A second ... $ #表示参数个数

• Mathematical Operation a=1;b=2; c=$ (($a + $b)) or $[$a + $b]

Shell basic Syntax (i)