learning bash shell

results of the parameter expansion, command substitution, and arithmetic expansion that do not occur in double quotation marks in order to divide the word.The shell nonalphanumeric each word of IFS as a delimiter, dividing the other unfolded results into words based on these characters. If IFS is not defined, or if its value is "An explicitly given null parameter ("" or ") will be retained. An implicitly null parameter that is not referenced from a p

In bash shell, the handling of arrays is an error-prone place.Array:Variable: Stores the memory space of a single element;Array: A contiguous memory space that stores multiple elements;Array nameIndex: Numbering starting from 0, is a numeric index;Note: Indexes can also support the use of custom formats, not just numeric formats;The bash array supports sparse for

[" $? " != "0" ];thenecho "$TCP _portnotanumber." exit1fiport_no_exists[$CURRENT _port]= $TCP _portforlsn_portin $CHK _tcp_cmddoif[ $TCP _port== $LSN _port];then unsetport_no_exists[$CURRENT _port]breakfidone ((current_port++)) doneif[${#PORT_NO_EXISTS [@]}-gt0];thenecho " Tcpports${port_no_exists[@]}failed. " exit1fiExit0 When used, the port number is added directly after the script as a parameter, and if multiple port numbers are scanned, each port number is separated by a space. If one of t

Shell's advantage: You can call Linux system commands directlyBasic syntax for shell scripts:Script name ends with. shThe first action of the program #!/bin/bash, tell the system this is a shell scriptWith # as a commentHow shell scripts are executed:Give script execution permission first, chmod;It is called directly w

Here's what you'll find useful after reading the third chapter of the Linux command line and Shell script programming encyclopedia.1./ETC/PASSWD file　　This file contains a list of all system user accounts and basic configuration information for each user, as shown in:　　　Each entry has seven fields, and the fields are separated by a colon, which includes:• User Name• User password (if the password is in another location, the bit is a placeholder)• User

of the parameters, that is, the value of the change $1,$2 ... $n, the values are rearranged in getoptEval set--"$TEMP"#经过getopt的处理, the specific options are processed below.While true; DoCase "$" in-a|--a-long) echo "Option a"; shift;-b|--b-long) echo "Option B, argument \ ' $ '"; Shift 2;;-c|--c-long)# C has an optional argument. As we is in quoted mode,# an empty parameter would be generated if it optional# argument is not found.Case "$" in"") echo "Option C, no argument"; Shift 2;;*) echo "O

Zhou haihan/Wen 2010.6.10 BASH Shell extension refers to an operation in which Shell expands commands when analyzing input commands. There are 7 extension methods. Refer to the man bash extension page: Expansion The braces (curly braces) extension method is also interesting. Example 1: operate a file with multiple f

Preface The basic languages I have mastered: PhP (most familiar with, the code in the project is implemented using it), bash shell (O M tool), and C (ACM dedicated ), it seems that only C can implement multithreading, but C is only used to learn and implement algorithms and data structures. Therefore, I want to simulate concurrent multi-process operations in my work, you can only rely on the

Three ways to start bash shell1, log in as the default login shell2. Interactive shell as a non-login shell3. As a non-interactive shell for running scriptsFirst, login shellWhen you log in to a Linux system, the bash shell starts as a login

Several possible causes:1 The user's home directory belongs to a group that has been renamed Root, and the solution uses root to perform Cd/home/;chown username:username username2 The user's home directory was modified, this time if you want to modify the user's home directory, first switch to the root user, directly modify the/etc/passwd file, find your user name that line, modify it, but after the change to enter the system again when the user name may display-

Preface or today to write an automated packaging script, using the path name to get the last file name. Here is a record of the implementation process. Of course, in the end I will also give the official approach. (PS: Very embarrassing, realized that the original bash Shell has a ready-made function)The get file name assumes that the given path name is:/tmp/csdn/zhengyi/test/zhengyi.txtThe awk solution use

First, Bash shell overview1. What is BashBASH is the abbreviation for the Bourne Again Shell, developed from the SH-unix system, and is a tool for users to interact with the Linux kernel, using the bash operation kernel to complete the system's use and management.Types of 2.shell