If judgment for Linux shell scripts

 

LinuxIf command

WhateverProgrammingLanguage is inseparable from conditional judgment. Shell is no exception. If list then Do something here Elif list then Do another thing here Else Do something else here Fi Ex1: #! /Bin/sh System = 'uname-S' # obtain the operating system type. If [$ system = "Linux"]; then # If it is Linux, print the Linux string Echo "Linux" Elif [$ system = "FreeBSD"]; then Echo "FreeBSD" Elif [$ system = "Solaris"]; then Echo "Solaris" Else Echo "what? " FI # ifend It is basically the same as other scripting languages. There is no big difference. However, it is worth noting that. [] Condition judgment. 1 string judgment Str1 = str2: true when two strings have the same content and length Str1! = Str2: true when str1 and str2 are different -N str1: true when the length of a string is greater than 0 (the string is not empty) -Z str1: true (empty string) when the string length is 0) Str1 is true when str1 is not empty 2. digit judgment Int1-EQ int2 two numbers are equal to true Int1-ne int2 two numbers are not true Int1-GT int2 int1 greater than int2 true Int1-ge int2 int1 greater than or equal to int2 true Int1-lt int2 int1 smaller than int2 true Int1-Le int2 int1 smaller than or equal to int2 true 3. File judgment -R file user readable to true -W file users can write to true -X file user executable is true -F file: the regular file is true. -D file: the directory is true. -C file: the special character file is true. -B file: The Block special file is true. -S file is true if the file size is not 0 -T file: this parameter is true when the specified device is a terminal in the file descriptor (1 by default ). 3. complex logic judgment -A and -O or ! Non End Although the syntax is simple, its functions become powerful when used in shell.