Shell Script Programming Basics

1. Create shell script file     Create file, add executable permission to file chmod +x file    format: Specify the shell        #! in the first line of the file /bin/bash    NOTES: #开头的命令 (except  #!/bin/bash  in the first line)     Display message: Echo command         Quotation marks are not required by default, and if you need to display a string that contains one of the single or double quotation marks, you can use a different string to make the difference.         echo command displays the string after the default line wrap, the-n option can be executed after the result of the next line of command is displayed         The environment variable reference in ECHO is automatically recognized and replaced with the actual value  $ (variable name)     User variable:        format: name=value, no spaces in the middle, The life cycle is the execution of the shell script, and the automatic deletion is done.     Back quotes ('): Gets the return content of the command to be executed         such as: times= ' Date '            &NBS P    echo "The data is:" $times                the data Is:mon Jan 31 20:2 3:25 EDT 2011    REDIRECT:        OUTPUT redirect: command > OutputFile  --overwrite write to file     &NB Sp                        command >> outputfile --Append to file         input redirection: Opposite to output redirection, using < or &LT;&LT, less common     piping: | , for the output of one command as input to another command, two commands for simultaneous execution 2, exit script     View exit status code: $? Saved the result of the previous command execution, 0 for success, 1~255 for error         Common status code--126: no permissions; 127: Command not found     Exit command: Exit status code, Used to exit the shell script and specify an exit code

Shell Script Programming Basics