Shell scripts ultrafast entry

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Shell Programming

Summary:

Shell is a program written in C, you can access the operating system kernel services by Shell user.

Shell is both a command language is a programming language

The Linux Shell interpreter many species, there may be a plurality of system shell, can / shells command to view the system installed by the shell interpreter cat / etc.

Since Bash free and easy to use, widely used in daily work. Meanwhile, Bash is the default most Linux systems Shell.

Shell naming variables?

Variable name must be a letter or an underscore character "_" at the beginning, followed by letters, numbers, or the underscore character. Do not use a?, *, Or other special characters to name your variables

Shell interpreter

java virtual machine interpreter needs, empathy shell script also needs parser

• [root@node04 shells]# cat /etc/shells
• /bin/sh
• /bin/bash
• /sbin/nologin
• /bin/dash
• /bin/tcsh
• /bin/csh

• Shell special characters used to process parameters What does it mean ?

  • $ 0 Current file name of the script
  • $ N arguments passed to the script or function. n is a number that represents the number of parameters. For example, the first parameter is $ 1, $ 2 is the second parameter.
  • $ # Number of arguments passed to the script or function.
  • $ * All parameters passed to the script or function.
  • $ @ All the parameters passed to the script or function. When the double quotes ( "") contains, and $ * is slightly different, the following will be mentioned.
  • $? Exit status of the previous command, or the return value of the function. In general, most of the command is successful returns 0, failure to return 1.
• Shell $$ current process ID. For Shell scripts, these scripts are located is the process ID

A writing shell scripts

① New /export/hello.sh file

#!/bin/bash

echo 'hello shell'                 

Solution:! # Convention is a tag that tells the system what the script requires an interpreter to perform that which Shell use.

  echo command for outputting the text window. 

Two shell scripts to perform a variety of ways

①

[root@node04 shells]# /bin/sh 01.sh
hello shell

②

[root@node04 shells]# /bin/bash 01.sh
hello shell

③

[root@node04 shells]#  ./hello.sh

hello shell