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. |