Shell

Shell is a command interpreter. It is an insulation layer between the operating system kernel and the user. To be precise, it is alsoA powerful computer language. A shellProgramIt is called a script and is a very easy-to-use tool.Combine system

The $ symbol in Bash is used to replace the parameter name with the value represented by the parameter. For $, braces are optional, that is, $ A and $ {A} represent the same parameter. $ {} There are several expressions with colons: $

Shell script debugging-run log 1   This article mainly describes how to output debug logs in shell scripts.   C/C ++ debug log In C/C ++, _ file __, _ FUNC __, _ line _ indicates which log of the current row comes fromSource codeWhich

Tangent to Vertex Returns a convex polygon.P, TangentLIsPIntersection andPInternalL. This concept is similar to orthogonal tangent. Pair of vertex points If two verticesPAndQ(BelongP) In the two parallel tangent lines, they form a pair of

$1 indicates the first parameter. $ * indicates all parameters entered by the user. The hello1 script is as follows. A location parameter is acceptable. #! /Bin/bash Echo $1   Run the Script:./hello1 "Hello World" and output Hello World on the

The Common commands of ADB shell in Android and the methods for viewing application database information under cmd are as follows: CMD -- ADB shell: Enter the shell command interface of the simulator. Ls displays all the file directories in the

1) Create FunctionName { ... } Or: Name (){ ... }   2) Call Use the function name directly. The function can be called only after it is defined; When a function has the same name, the new definition will overwrite the old definition and no

Shell scripting is an interpreted language; The essence of shell scripts is an ordered set of shell commands; 1. Basic shell programming process 1) create a shell file 2) grant executable permissions to chmod A + x filename 3) execute the shell file.

Example: #! /Bin/sh Mypath = "/var/log/httpd /"Myfile = "/var/log/httpd/access. log" # Here, the-x parameter determines whether $ mypath exists and has executable permissions.If [! -X "$ mypath"]; thenMkdir "$ mypath"Fi # Here, the-D parameter

In awk programming, do not forget that awk processes regular expressions. There are many internal functions, especially string processing functions. Calling these functions can reduce the workload. 1. Format // Note \ There cannot be spaces behind

Chapter 2: handling user input Command Line ParametersRead ParametersBASH Shell assigns some special variables called positional parameter to all the parameters entered by the command line.Even include the program name$0: Program name (Absolute

Chapter 2: using structured commands Use the if-then statement if commandthen commandsfi If the exit status code of the command after if is 0, execute then. Another Form if command; then commandsfi   If-then-else statement if commandthen

Shell sorting is a form of change in insert sorting. Because insert sorting compares each element and compares the current element with all the previous elements, in the worst case. Therefore, DL. shell proposed shell sorting in 1959, that is,

  Some terminal shortcut keys: CTRL + F Forward one character CTRL + B Move one character behind CTRL + E Move to end of line CTRL + L Clear Screen CTRL + d Delete current

1. condition test Two formats: test condition or [condition] (Note that spaces are added on both sides)Condition can be a logical operation of multiple sub-conditions. The logical operator numbers include: -A logic and -O logic or ! Logic No &, | 2.

 FindSearch for files or directories. Syntax: Find [directory...] [-Amin ] [-anewer ] [-atime ] [-Cmin ] [-cnewer ] [-ctime ] [-daystart] [-depyh] [-empty] [-exec ] [-false] [-FLS ] [-follow] [-fprint ] [-fprint0 ] [-fprintf ] [-fstype ] [-gid ]

Shell script used to detect Processes 10:38:08 | category: centos | font size subscription Script 1: #! /Bin/sh Program = XXXX # process name Sn = 'ps-Ef | grep $ program | grep-V grep | awk '{print $2} ''# obtain the process port numberIf ["$ {sn}"

#! /Bin/sh # Filename: 2.sh B = 9 E = 15 Tmpb = $ B While [$ tmpb-Le $ E] Do Echo $ tmpb # Tmpb = 'expr $ tmpb + 1' // OK Tmpb = $ (expr $ tmpb + 1) Done After the script is executed, the output result is: 9101112131415   Note: The

To determine whether the variables in a script are empty, I wrote a shell script like this: #! /Bin/sh # Filename: Test. Sh Para1 = If [! -N $ para1]; then Echo "is null" Else Echo "not null" Fi Then run the Script: test. sh uses

Linux system resource load is too high and Apache shell script is automatically restarted   When we routinely maintain Apache Web servers in Linux, the endless loop caused by crawler crawling cannot jump out, or the collection of data from peers