当前位置:网站首页>Chapter 4.1 shell programming basis

Chapter 4.1 shell programming basis

2020-11-10 11:31:08 Super director Li

  linux The control of the system is controlled by the kernel to allocate resources ,shell Commands are tools for communicating with kernel operations .shell There are many types of , common /bin/sh、/bin/bash, stay centos Environment   By default bash, Other forms of... Are not recommended shell.

  1) Historical record

  bash shell When use , It will automatically record the command operated , The records are kept in .bash_history In file . Recent naming history 1000 strip , Can pass profile Set up HISTSIZE Adjust the length of the record , For example, you can set the number of records to 10000 /HISTSIZE=10000. When querying a used command , have access to Ctrl+r The shortcut key opens the command search , But in daily management, it is recommended to use history  or history|grep xxxx Command find .

  2) Shortcut key

   In command line shell interface , The command line can use the following shortcut keys , Improve operation efficiency .

    Ctrl+a    Move the cursor to the beginning of the line
    Ctrl+e    Move the cursor to the end of the line
    Ctrl+l     Clear the screen
    Ctrl+c    Terminate the process
    Ctrl+z    Suspend process
    Ctrl+u    Delete the character from the cursor to the beginning of the line
    Ctrl+k    Delete the characters from the cursor to the end of the line
    Ctrl+f    Move the cursor one character to the right
    Ctrl+b    Move the cursor one character to the left
    Ctrl+w    Delete the character before the cursor
    Alt+d     Delete the character after the cursor
    Tab       Automatic completion

  3) The alias set

   linux Allow users to set the alias of the command according to their own needs . such as ,ll The command is 'ls -l --color=auto' Abbreviation , Alias complex commands , It can improve the efficiency of operation . Enter... In the command line interface alias  You can view the command aliases that have been set ; For example, setting an alias : alias nginxstart='systemctl start nginx',nginxstart  You can start it directly nginx 了 ; Remove alias :unalias nginxstart.

  [root@centos7 yum.repos.d]# alias nginxstart='systemctl start nginx'
  [root@centos7 yum.repos.d]# alias
  alias cp='cp -i'
  alias egrep='egrep --color=auto'
  alias fgrep='fgrep --color=auto'
  alias grep='grep --color=auto'
  alias l.='ls -d .* --color=auto'
  alias ll='ls -l --color=auto'
  alias ls='ls --color=auto'
  alias mv='mv -i'
  alias nginxstart='systemctl start nginx'
  alias rm='rm -i'
  alias which='alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde'
  [root@centos7 yum.repos.d]# unalias nginxstart

  4) Pipe, ---“|”

    The pipe character is used to connect multiple commands , The result of the previous command is standard output to the standard input of the next command . for example ,cat /etc/passwd |grep bash Commands can be filtered out to have bash Users with login rights , direct cat see passwd When it comes to documentation , There is a lot of output , Inconvenient to view with bash Permission information , When you add pipes | after , Then use grep Command filtering cat Output information , Finally, it was screened out with bash Information line of .

  5) Redirect ---“> ,>>”

    The function of the redirection symbol is to output the result of the command to the specified file or location .> It's mandatory coverage mode , No file will automatically create a file , Documents , File contents will be overwritten ;>>  Is append mode output to file ; The number at the end of the command also has a special meaning ,0 For standard input ,1 For standard output ,2 Represents standard error ;2>&1  To redirect standard error to standard output ;> /dev/null  It's writing output to an endless black hole , The processing of user's uninteresting information .

  [root@centos7 ~]# history > /tmp/1.txt
  [root@centos7 ~]# cat /etc/nginx.conf >>/tmp/1.txt
  [root@centos7 ~]# nohup ./rmlog.sh > rm.log 2>&1 &
  [root@centos7 ~]# sh mysql.sh >/dev/null 2>&1

  6) Sequence controller ---“&”

  & yes shell The characters commonly used in , Add... After an order &, It means running in the background ;&& Can connect two commands , It means that only if the current command is successfully executed, the following command will be executed ;|| It means that when the previous command fails to execute, the following character will be executed .

  [root@centos7 ~]# nohup /home/jiankong.sh &    # The background does not interrupt the execution

  7) quotes

   Single quotation marks can be used to restore the literal meaning of a character , The function of shielding metacharacter is realized , Single quotation marks must be used in pairs ; Double quotation marks are basically the same as single quotation marks , But it doesn't block $ ' \ The function of these three metacharacters , If you want to block , It has to be preceded by a \; Backquotes are command substitution , Replace the command character with the command result output .

  [root@centos7 ~]# echo '$JAVA_HOME'      # To achieve shielding $ Special features of
  [root@centos7 ~]# echo 'cd \home'        # Implementation of shielding escape characters
  [root@centos7 ~]# echo "$JAVA_HOME"       # Double quotation marks output variables directly
  [root@centos7 ~]# echo "\$JAVA_HOME"     # use \ escape , Directly output the following characters
  [root@centos7 ~]# echo "today is `date`"      # Direct output date Results of command

  8) Variable

    Variables have environment variables 、 Common variables 、 Special variables . Environment variables generally refer to system environment variables , Just include the user 、 Catalog 、 route 、 Global parameters, etc , They need to execute export Statement can be used only , use env The command can view these variables . Ordinary variables are mainly the assignment of parameters to be called by the application . The special variable is linux Specific parameter variables set by the system . In daily application, the most important thing is to declare environment variables , Assignment variables are also used in scripts , Special variables are used less . Here are examples of three variables .

  java Example of setting environment variables
  [root@centos7 ~]# vim /etc/profile
    JAVA_HOME=/usr/local/java
    JRE_HOME=/usr/local/java/jre
    CLASS_PATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar:$JRE_HOME/lib
    PATH=$PATH:$JAVA_HOME/bin:$JRE_HOME/bin
    export JAVA_HOME JRE_HOME CLASS_PATH PATH
  [root@centos7 ~]# source /etc/profile

   Examples of commonly used assignment variables in scripts
  [root@centos7 ~]# starttime=`date`
  [root@centos7 ~]# gameuser="lixiaoming"
  [root@centos7 ~]# fr_1='12315'

   Definition of special variables
  $0    Get script file name
  $n    For the first n Parameter values ,$1 Is the first parameter ,$2 It's the second parameter ...
  $#    Get the total number of parameters
  $*    Get the parameter passed ,"$*" Represents the parameter as a single string , With "$1 $2 ... $n" Formal output parameters
  $@   Get the parameter passed ,"$@" Indicates that the parameter is treated as a separate string , With "$1" "$2" "$3" ... "$n" Formal output parameters
  $?    Gets the execution status of the previous command ,0 It means success , Others are failures
  $$    Get the process number of the current script or command
  $!    Get the process number of the last background process

  9) Array

   Array is a data structure with variable function , An array consists of elements , Each element is assigned a zero based integer index . There are two ways to define an array , One is to assign values one by one , Such as TESTA[0]=100,TESTA[1]=200; The other is to create a full value assignment , Such as TESTB=(12 23 34 45), Take the value of $TESTB[1]. Use the following example to deepen your understanding of arrays .

  root@centos7 ~]# TESTB=(12 23 34 45)       # Define a new array
  [root@centos7 ~]# echo ${TESTB[2]}       # The output index is 2 The element value of
  [root@centos7 ~]# TESTB[4]=56           # Add the index to 4 New elements of
  [root@centos7 ~]# echo ${TESTB[@]}       # Output all elements , Space separates the element value format
  [root@centos7 ~]# echo ${TESTB[*]}       # Output all elements , String format
  [root@centos7 ~]# echo ${#TESTB[@]}     # The number of elements in the output array
  [root@centos7 ~]# echo ${#TESTB[*]}       # The number of elements in the output array
  [root@centos7 ~]# TESTC=(${TESTA[@]} ${TESTB[@]})   # Two arrays are merged into a new array

  10) Arithmetic operations

  Bash Supports many operators , Including arithmetic operators 、 Relational operator 、 Boolean operator 、 String operators and file test operators .

  1 Arithmetic operations
   Native bash Simple mathematical operations are not supported , But it can go through expr Command to implement expr Is an expression calculation tool , It can complete the evaluation of expressions
  a=10
  b=20
   Common arithmetic operators
  +    Add    `expr $a + $b`   The result is 30
  -    Subtraction    `expr $a - $b`    The result is 10
  *    Multiplication    `expr $a \* $b`    The result is 200
  /    division    `expr $b / $a`    The result is 2
  %    Remainder    `expr $b % $a`    The result is 0
  =   assignment      a=$b      Will put the variable b The value is assigned to a
  ==    equal   Used to compare two numbers , Same returns true,[ $a == $b ] return false
  != It's not equal Used to compare two numbers , If not, return to true,[ $a != $b ] return true
   Be careful : Conditional expressions should be placed between square brackets , And there should be spaces , for example [$a==$b] It's wrong. , Must be written as [ $a == $b ]
  
  2 Relational operator
   Operator          explain                 give an example
  -eq   Check whether two numbers are equal , Equal return true      [ $a -eq $b ] return false
  -ne   Check whether two numbers are equal , Unequal return true    [ $a -ne $b ] return true
  -gt   Check whether the number on the left is greater than that on the right , Is to return true    [ $a -gt $b ] return false
  -lt   Check whether the number on the left is less than that on the right , Yes, go back to true    [ $a -lt $b ] return true
  -ge   Check whether the number on the left is greater than that on the right , Yes, go back to true  [ $a -ge $b ] return false
  -le   Check whether the number on the left side is less than or equal to that on the right side , Yes, go back to true  [ $a -le $b ] return true
  
  3 Boolean operator
   Operator        explain                    give an example
   !    Non operation , Expression for true Then return to false, Otherwise return to true    [ ! false ] return true
  -o   Or operations , There is an expression for true Then return to true      [ $a -lt 20 -o $b -gt 100 ] return true
  -a    And operation , Both expressions are true To return to true      [ $a -lt 20 -a $b -gt 100 ] return false
  
  4 String operators
   Operator        explain                  give an example
  =    Checks if two strings are equal , Equal return true      [ $a = $b ] return false
  !=    Checks if two strings are equal , Unequal return true    [ $a != $b ] return true
  -z    Check if the string length is 0, by 0 return true      [ -z $a ] return false
  -n    Check if the string length is 0, Not for 0 return true      [ -n $a ] return true
  str    Check if the string is empty , Not empty return true      [ $a ] return true
  
  5 File test operators
   The operator explain give an example
  -b file    Check if the file is a block device file , If it is , Then return to true     [ -b $file ] return false
  -c file    Check whether the file is a character device file , If it is , Then return to true    [ -b $file ] return false
  -d file    Check if the file is a directory , If it is , Then return to true        [ -d $file ] return false
  -e file    Detect the existence of files or directories , If it is , Then return to true      [ -e $file ] return true
  -f file    Check if the file is a normal file , If it is , Then return to true       [ -f $file ] return true
  -g file    Check if the file is set SGID position , If it is , Then return to true    [ -g $file ] return false
  -h file    Check if the file is a linked file , If it is , Then return to true      [ -h $file] return false
  -k file    Check whether the file is set with the adhesive bit ( If it is , Then return to true      [ -k $file ] return false
  -p file    Check whether the file is a named pipe , If it is , Then return to true      [ -p $file ] return false
  -u file    Check if the file is set SUID position , If it is , Then return to true    [ -u $file ] return false
  -r file    Check whether the file is readable , If it is , Then return to true        [ -r $file ] return true
  -w file    Check whether the file is writable , If it is , Then return to true        [ -w $file ] return true
  -x file    Check if the file is executable , If it is , Then return to true      [ -x $file ] return true
  -s file    Check if the file is not empty , Not empty , return true       [ -s $file ] return true

  11) The basis of regular expression

  1 Regular common command tools
  grep、egrep、sed、awk

  2 The basic regular expression of symbolic meaning
   d       Match the letter d
   .       Match any single character
   *       Match one or more
   .*       Match any number of characters
   ^       Match the beginning of the string
   $       Match the end of the string
   []       Matches any single character in the set
   [^]       Match negation , Negate the set in brackets
   [x-y]       matching x To y Continuous string ranges
   \      Match the escaped string
   \{n,\}   Match the previous character and repeat at least n Time
   \{n\}    Match the previous character and repeat n Time
   \(\)    call \( and \) Content between
  
  3 Expression for check character
  1 Chinese characters :  ^[\u4e00-\u9fa5]{0,}$
  2 English and numbers :  ^[A-Za-z0-9]+$ or ^[A-Za-z0-9]{4,40}$
  3 The length is 3-20 All characters of :  ^.{3,20}$
  4 from 26 A string of English letters :  ^[A-Za-z]+$
  5 from 26 A string of uppercase letters :  ^[A-Z]+$
  6 from 26 A string of lowercase letters :  ^[a-z]+$
  7 By numbers and 26 A string of English letters :  ^[A-Za-z0-9]+$
  8 By digital 、26 A string of English letters or underscores :  ^\w+$ or ^\w{3,20}$
  9 chinese 、 english 、 Numbers include underscores :  ^[\u4E00-\u9FA5A-Za-z0-9_]+$
  10 chinese 、 english 、 Number but excluding symbols such as underscores :  ^[\u4E00-\u9FA5A-Za-z0-9]+$
  11 Can be entered with ^%&',;=?$\" Equal character :  [^%&',;=?$\x22]+
  12 Disable input containing ~ The characters of :  [^~\x22]+
  
  4 Expression of special requirements
  Email Address :  ^\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$
   domain name :  [a-zA-Z0-9][-a-zA-Z0-9]{0,62}(/.[a-zA-Z0-9][-a-zA-Z0-9]{0,62})+/.?
  InternetURL:  [a-zA-z]+://[^\s]* or ^http://([\w-]+\.)+[\w-]+(/[\w-./?%&=]*)?$
   Phone number :  ^(13[0-9]|14[5|7]|15[0|1|2|3|5|6|7|8|9]|18[0|1|2|3|5|6|7|8|9])\d{8}$
   Phone number ("XXX-XXXXXXX"、"XXXX-XXXXXXXX"、"XXX-XXXXXXX"、"XXX-XXXXXXXX"、"XXXXXXX" and "XXXXXXXX):^(\(\d{3,4}-)|\d{3.4}-)?\d{7,8}$
   Domestic phone number (0511-4405222、021-87888822):  \d{3}-\d{8}|\d{4}-\d{7}
  15 or 18 position ×××:  ^\d{15}|\d{18}$
  15 position ×××:  ^[1-9]\d{7}((0\d)|(1[0-2]))(([0|1|2]\d)|3[0-1])\d{3}$
  18 position ×××:  ^[1-9]\d{5}[1-9]\d{3}((0\d)|(1[0-2]))(([0|1|2]\d)|3[0-1])\d{4}$
   short ××× number ( Numbers 、 Letter x ending ):  ^([0-9]){7,18}(x|X)?$ or ^\d{8,18}|[0-9x]{8,18}|[0-9X]{8,18}?$
   Is the account number legal ( Beginning of letter , allow 5-16 byte , Allow alphanumeric underscores ):  ^[a-zA-Z][a-zA-Z0-9_]{4,15}$
   password ( Start with a letter , The length is in 6~18 Between , Can only contain letters 、 Numbers and underscores ):  ^[a-zA-Z]\w{5,17}$
   Strong password ( Must contain a combination of upper and lower case letters and numbers , Special characters cannot be used , The length is in 8-10 Between ):  ^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).{8,10}$
   Date format :  ^\d{4}-\d{1,2}-\d{1,2}
   One year 12 Months (01~09 and 1~12):  ^(0?[1-9]|1[0-2])$
   A month 31 God (01~09 and 1~31):  ^((0?[1-9])|((1|2)[0-9])|30|31)$
   tencent QQ Number :  [1-9][0-9]{4,} ( tencent QQ Number from 10000 Start )
   China Post Code :  [1-9]\d{5}(?!\d) ( China Post code is 6 Digit number )
  IP Address :  \d+\.\d+\.\d+\.\d+ ( extract IP Useful for addresses )

 

版权声明
本文为[Super director Li]所创,转载请带上原文链接,感谢