shell awk

shell

 What is? shell Script  :
1. When the command is not executed on the command line , But when executing from a file , The file is shell Script .	shell Scripts are plain text files , It consists of process control logic and commands .	shell Scripts usually use .sh Suffixed name , But it's not necessary .
2.Shell It's an interpretive programming language , No compilation required , It is also executed by line .       
3.Shell Scripts are interpreted and executed by the interpreter , Common interpreters are ：	bash dash ash  ksh  sh etc.     Be careful , Each of these Shell The interpreter is right shell The grammatical interpretation of is not exactly the same (sh and bash The parser is right ll The explanation is different ), But basically the same .
4.  A script is a stack of commands 5.  Scripts can take parameters , There are variables, too , There can also be process control and even functions 

 Position parameter variable :
  1. Positional parameters are a special set of built-in variables , Each string separated by a space following the script name 	$1  It means the first one 1 Parameter values ,……,$9  It means the first one 9 Parameter values 	${10}  It means the first one 10 Parameter values , ${11}  It means the first one 11 Parameter values 	
  2. Role of position parameters 	     from  shell  command / Script   The command line of accepts parameters 	    Calling  shell  Pass parameters to function 
  
    Special variables :
   1. Related to command line parameters 	
   $*      Treat all position parameters as a string （ In space ） .String str= "1  2  3  4"	
   [email protected]    Treat each position parameter as a separate string （ In space ）.	"1" "2 " "3"  "4" 	
  “$*”    Treat all position parameters as a string （ With $IFS interval ）.	
  “[email protected]”  Treat each position parameter as a separate string （ In space ） .       $0     Entered on the command line Shell The program name .	 
   $#     Indicates the number of parameters on the command line .
   2. Related to process status 	
   $?   Represents the return value of the last command 	
   $$   The process number of the current process 	$!    Displays the of the last job running in the background  PID	
   $_   The last parameter of a command or script executed before 	 Examples of location parameters and special variables , Execute the script  
   
   
    Improve the package backup function ：
    establish sh file    touch pack.sh
   #!/bin/bash     Declaration parsing , Used to parse commands 
   # pack , And handle exceptions , When the backup package succeeds , Delete the original directory 
   # 2 Represents the execution of the previous name if there is an error  &&  When the previous command is executed successfully , Execute the following command 
   tar -czvf $2   $1  2>error.log && rm -rf $1 || cat error
    Then exit the editor , Modify user rights 
   chmod u+x pack.sh       
    Carry out orders ：
   ./pack.sh    Compressed files      Compressed prefix name 
   ls Check whether to compress and delete 
   
  
   sign out / Return to status ：
  1.$?： Returns the status of the last statement or script execution 	0： success 	1－255： You don't succeed 
  2.exit  The command is used to exit the script or the current Shelln  It is a slave.  0  To  255  The integer of 0  Indicates a successful exit , Non zero means that some failure return value is encountered   Saved in state variables  $?  in 
  
  
    Common return status codes ：
   0：	  Execute correctly 	 
   1：      General error 	
   126：	  Command or script does not have execution permission 	
   127：	  The order was not found 	
   2 :	  Parameter does not exist 
  
   
    Stream redirection ：
    The standard input ： Code 0, Use  <  perhaps  <<
    standard output ： Code 1, Use   >  perhaps  >>
    Error output ： Code 2, Use  >  perhaps  > >
   >  Express   write in   >> Indicates append 
   < Express   Read in  << Indicates end of read in 
   cat<b.log>c.log          Read b.log Document content to c.log in 
   cat <<EOF >>c.log          Read EOF The content between is appended to c.log
    It is generally used for the combination of two files 
   
   
    Continuous execution of commands  
   &&： Execute the following command after success 
   ||： Execute the following code after the previous code fails 
    if else    if elseif    for  while  
     Greater than  -gt (greater than)       
     Less than  -lt (less than) 
     Greater than or equal to  -ge (greater than or equal) 
     Less than or equal to  -le (less than or equal) 
     It's not equal  -ne （not equal）  

Common commands awk

awk brief introduction ：
1.awk Is a very good data processing program , It tends to divide a line into multiple ‘ Field ’ To deal with it . similar    String[] strArray = "a,b,c,d".split(","); strArray[0]   strArray[3]	
2. Data can come from standard inputs 、 One or more files 、 Output of other processes 	
3.awk From 1 Line by line scanning to the last line , And perform matching operations 	
4.awk The default operation of is to output matching lines, that is, print matching lines to standard output 

awk grammar ：
1.awk  [ Options ]   'BEGIN{ sentence 1; sentence 2;...}  END{ sentence 1; sentence 2;...}     Pattern 1{ sentence 1; sentence 2;...}   Pattern 2{ sentence 1; sentence 2;...}   Pattern n...'    [ file name ]
awk 'BEGIN{print " File start ";} END{print " End of file ";} {print " Executive line " NR}'  tomcat.log        

practice ：

Write a script , The functional requirements are as follows ：
Script runtime , You can enter multiple parameters
1, When the script enters parameters , The first parameter is 1 when , The second parameter is the path to package , The third parameter is the packed file name , Realize the function of dynamically packaging and backing up any directory and deleting the original files
2, When the script enters parameters , The first parameter is 2 when , The second parameter is the directory path to traverse , Traverse all files under the directory of dynamic input and output the results
3, When the script enters parameters , The first parameter is 3 when , The second parameter is a positive integer , Achieve summation 1 To the function of the sum of the positive integer parameters
4, When the script enters parameters , When the first parameter is other , Input error of output parameters

#!/bin/bash
if [ $1 -eq 1 ] ; then
tar -czvf $3.tar.gz $2 2>error.log && rm -rf $2
elif [ $1 -eq 2 ] ; then
ls -l $2
elif [ $1 -eq 3 ] ; then
declare -i sum=0;
declare -i j=1;
while (( j<=$2))doletsum+=j;letj++;doneecho"totalandyes：$sum "
else
echo 'error ’
fi