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Linux System Administration phần 3

An ninh là chặt chẽ hơn trên các hệ thống Debian mặc định hơn bất kỳ những người khác mà chúng ta đã cài đặt. Debian người sử dụng có xu hướng giống như có kiểm soát nhiều hơn đối với sự phát triển của nó hơn so với phân phối khác. Trang Web của Debian được đặt tại | the application. Instead of the wildcard characters for instance the program would receive a space-delimited list of all files matching the wildcard construct. The user may restrict this capability if the wildcard characters are intended to be interpreted by the program rather than the shell. There are three wildcard characters frequently used in Linux each interpreted differently by the Bash shell the asterisk the question mark and the bracket pair. The asterisk is often called the splat the string b .bmp might be pronounced as b-splat-dot-bmp. Its purpose is to replace a string of any number of characters in sequence. Thus b .bmp matches with any file whose name begins with b and has the .bmp extension. The files blue.bmp barney.bmp bermuda.bmp and before_you_go_away.bmp would all match. The string . matches all files that contain a period be certain that you really mean to act on all files in the directory when you use this string. The string . matches any dot file. Many a user has deleted important files by specifying an incorrect wildcard string as an argument to the rm command. The joke that is often played is trying to get the new guy to run rm -rf from the root directory. This is a forced removal of all files and directories. It s ugly if you have no backup. The question mark represents any one character. The string file_ would match all of the following file_1 file_2 file_A or file_b. The string file. would match any file named file that has a three-character extension. The bracket pair is used to define a list or range of characters to be matched. The string file 0-9 would match file0 file1 file9. The string a-zA-Z would match any single alphabetical character. The string a-zA-Z0-9 would match any alpha or numeric character. Quoting As you ve seen shell commands assign special meanings to ordinary alphanumeric characters so when these characters are used within strings literally there needs to be some way to prevent the shell from interpreting the .