Use brackets in linux to determine conditions

In linux, brackets are used to determine the format # representing spaces. [# param1 # op # param2 #] is indispensable in the form of a comparison operator, which must be separated by spaces between the left and right sides of op. for example, if [#32 #] is a write method without spaces, the result is true. of course, the result is false. w...
In linux, brackets are used for condition determination. the format "#" represents space. [# param1 # op # param2 #] is indispensable in the form of a comparison operator, which must be separated by spaces between the left and right sides of op. for example, if [# "3" = "2" #] is missing spaces, the result is "true". of course, the result is actually "false ". the variables www.2cto.com should be enclosed in double quotation marks [#-z "$ name" #]. * ******************* name = "Jim" [$ name = "Jack"] # it will become [jim = "Jack"], an error occurs. * ******************* constants should be enclosed in double quotation marks or single quotation marks [# '1' #==#'10 '#]. better writing method: ******************************. each component in the brackets is separated by a space (which can be described as a base salary) B. variables are enclosed in double quotation marks ******* * ******************** Www.2cto.com parameter-B if the file exists and is a special block file, true-c file if the file exists and is a special character file, true-d file if the file exists and is a directory, true-e file if the file exists, true-f file if the file exists and is a rule file, true-g file if the file exists and the SGID bit value is set, true-h file. if the file exists and is a conforming link, true-k file if the file exists and the "sticky" bit value is set-p file if the file exists and is a named pipe, true-r file if the file exists and is readable, true-s file if the file exists and its size is greater than zero, true-u file if the file exists and the SUID bit is set, true-w file if the file exists and can be written, true-x file if the file exists and is executable, true-o file is true if the file exists and is owned by a valid user ID. -Z string if the string length is 0, true-n string if the string length is not 0, true string1 = string2 if the two strings are equal, true string1! = String2 if the two strings are not equal, it is true that www.2cto.com ************************************* * ******************** the numbers involved in the comparison must be converted to integers, do you have manual with this syntax? Int1-eq int2 if int1 is equal to int2, true int1-ne int2 if int1 is not equal to int2, true int1-lt int2 if int1 is less than int2, true int1-le int2 if int1 is smaller than or equal to int2, true int1-gt int2 if int1 is greater than int2, true int1-ge int2 if int1 is greater than or equal to int2, it is true ************************************** ********************! If expr is false, the composite expression is true. Expr can be any valid test expression expr1-a expr2 if both expr1 and expr2 are true, the entire formula is true expr1-o expr2 if expr1 and expr2 have one true, the entire formula is true www.2cto.com, in your example, do not mind ^_^ when the user inputs Y/y, the output is "OK, continue". when the user inputs N/n, the output is "Oh, interrupt!" When the user inputs other characters or is empty, the output "I don't know your command !"