Shell Scripting Learning Guide

Entry

• Awk and Bourne shell are the basis of POSIX shell
• In addition to the POSIX standard, there are European x/open standards
• Two types of regular expressions
  
  • BRE basic Regular Expressions basic grep use
  • ERE Extended Regular Expressions Extensibility Egrep Use
• Small shell script development, first, directly in the command line test, and then put a series of commands into the script, and set the executable permissions, and finally use the script

$ cat > users       #建立文件，使用cat复制终端的输入    who | wc -l     #程序的内容    ^D              #Ctrl + D表示end-of-line$ chmod +x nusers   #让文件拥有可执行权限$ ./nusers          #执行    6$ cat nusers        #文件内容    who | wc -l

• "#!" in the first line of the shell script

#! /bin/sh     #告诉系统用哪种Shell解释#! /bin/sh -f  #-f表示执行脚本的参数，后面不能有空格，空格会跟着选项一起传给程序   /bin/sh -f /bin/ls -la#! /bin/awk -f #声明一个awk脚本，参数为-f#! /bin/sh -   #表示没有选项。这是基于安全的考虑，可避免欺诈攻击

• Shell command-line arguments
  
  • Options that do not require parameters, you can merge
  • Separate multiple commands in the same line with semicolons
  • Shell basic Commands
    
    • Built-in commands
    • Shell functions
    • External Command--shell initiates a new process to execute the external command, and after execution, the process of returning to the shell continues execution
  • $ plus number, indicating the parameters of the script
  • If the argument exceeds 9, enclose it in curly braces ${10}

lsls -la

• Variable
  
  • Start with a letter or underscore
  • The variable can be null, and the null value is NULL
  • When assigning a variable, there must be no spaces around the equals sign
  • Gets the value of the variable, preceded by $; If the value contains a space, enclose it in quotation marks

#! /bin/sh -var1=1          #=>1var2=aaa        #=>aaavar3="bbb"      #=>bbbvar4="aaa bbb"  #=>aaa bbbvar5 =1         #=>错误2         #=>错误

• Output
  
  • Echo
    
    • Simple output, end with line break
    • -N option, omitting the last line break
    • echo command standard is not uniform, so portability is problematic, only use this command to do the simplest output, do not use complex parameters
  • Printf
    
    • You must specify a newline character to be displayed.

#! /bin/sh -echo"Hello World!"                 #=>Hello World!printf"Hello World! i = [%d]\n"3  #=>Hello World! i = [3]

• io redirection
  
  • > redirect standard output
  • < REDIRECT standard input
  • >> append to file
  • | pipeline
  • /dev/null reads/dev/null and immediately returns EOF
• Basic Command Lookup
  
  • Shell finds the command to execute in the environment variable $path
  • $PATH, Empty project with:: Represented, representing the current path
  • starts with: Indicates the current path is first
  • to: End, indicates the last find current path
  • use. Instead of empty items, enhanced readability
  • should not put the current path in the lookup path because of security issues
• Execute trace
  
  • Print Statements executed by the Shell
  • SET-X Start Tracking
  • St +x de-tracking

#!/bin/sh- set -xecho  " 111 " set  +xecho   "222"   #输出:  + echo  111  111  + set  +x 222   

• internationalization and localization
  
  • internationalization i18n
  • localization l10n
  • locale environment variable
    
    • LANG does not set the default value when any lc_xxx
    • Lc_all is used to override the value of all other lc_xxx variables
    • lc_collate collation
    lc_ctype Character Set
    • lc_messages message and response (POSIX only)
    • lc_monetary currency
    • lc_numeric number
    • lc_time time and date
  The
  • should avoid assigning a value to any of the lc_xxx variables
  • locale-a
    
    • lists all locale names
  • lc_all=da locale-ck lc_time
    
    • query Danish time and date format
• commands involved
  
  • who commands
    
    • display who are logged in
  • TR
    
    • tr is used to convert character conversions from standard input through substitution or deletion
  • stty
    
  • locale
    
    • display locale settings

# Replace the "ABC" that appears in the file with "XYZ"Cat file| tr "Abc" "Xyz"> New_file# Use the TR command to "unify" the case of lettersCat file| tr [A-z] [a-z] > New_fileCat file| tr [A-z] [a-z] > New_file# Replace the number 0-9 in the file with A-jCat file| tr [0-9] [a-j] > New_file# Delete the "Snail" characters that appear in file filesCat file| tr-d "Snail"> New_file"Note" Here, the ' S ', ' n ', ' a ', ' I ', and ' l ' characters that appear in the file files will be deleted! Instead of tightly deleting the resulting"Snail" string# Remove the newline ' \ n ' and the tab ' \ T ' characters that appear in file files, and the invisible characters must be represented by the escape characterCat file| tr-d "\n\t"> New_file# Delete "consecutive" repeating letters, leaving only the first oneCat file| tr-s [a-za-z] > New_file# Delete empty linesCat file| tr-s "\ n"> New_file# Delete windows file "Cause" the ' ^m ' characterCat file| tr-d "\ r"> New_fileCat file| tr-s "\ r"  "\ n"> New_file"Note" Here-S is followed by two parameters"\ r"And"\ n", replace the former with the latter# Replace tabs with space \040 \011Cat file| tr-s "\011" "\040"> New_file# Replace the colon ":" in the path variable with the line break "\ n"Echo $PATH| tr-s ":" "\ n"

Shell Scripting Learning Guide