Tài Liệu - Võ Tấn Dũng (votandung) Unit2 Linux ITC

Information Technology College of HoChiMinh city Faculty of Information Technology Course: Fundamentals of Linux OS Unit Accessing Files and Directories Lecturer: Võ Tấn Dũng votandung@yahoo.com http://sites.google.com/site/votandungsg/ Objectives Upon completion of this module you should be able to: • Contrast absolute and relative pathnames • Access files and directories within the file structure using absolute and relative pathnames • Identify and describe the parts of a command line • Access files and directories within the file structure using pathname abbreviations • List the contents of directories and their file types • Identify various meta-characters • Enter more than one command on a single command line • Demonstrate the use of wildcard characters VÕ TẤN DŨNG Pathnames • A pathname uniquely identifies a particular file or directory by specifying its location VÕ TẤN DŨNG Absolute Pathname - An absolute pathname specifies a file or directory in relation to the entire Linux file hierarchy The hierarchy begins at the / (root) directory - Absolute pathnames always: • Start at the root (/) directory and list each directory along the path to the destination file (or directory) • Use a slash (/) between each directory name in the path to indicate different directories Example: /home/user2 /home/user2/dir1 /home/user2/dir1/coffees VÕ TẤN DŨNG Relative Pathname • A relative pathname describes the location of a file or directory as it relates to the current directory • If you are in a directory and you want to move down the directory tree, it is not necessary to type the absolute pathname • You can just type the path starting with the name of the next directory in the directory structure • If a pathname does not begin with a slash, it is a relative pathname VÕ TẤN DŨNG Relative Pathname (cont.) • A relative Pathname starts from a direct child directory of the current directory to the destination • Relative pathnames are useful because they are shorter than absolute pathnames Example: The current directory /home Relative pathname to user2 user2 Relative pathname to dir1 user2/dir1 Relative pathname to coffees user2/dir1/coffees VÕ TẤN DŨNG Changing Directories using the cd command • Files you need to access are often stored in a given subdirectory, it is often desirable to change directory locations • Use the cd command to change to a new current directory The cd command accepts both absolute and relative pathnames Command Format cd [directory_name] Example: With an absolute pathname $ cd /home With a relative pathname $ cd user2/dir1 Use the cd command without a directory name to return to your home directory $ cd VÕ TẤN DŨNG Displaying the Current Directory using the pwd command • Remembering which directory you are currently working in is often difficult Use the pwd (print working directory) command to display the absolute pathname of your current directory Example: $ pwd /home/user2 $ cd /home $ pwd /home $ cd $ cd practice $ pwd /home/user2/practice VÕ TẤN DŨNG Pathname Abbreviations Example: $ pwd /home/user2/dir1 $ cd $ pwd /home/user2 $ cd / $ pwd / $ cd ~/practice $ pwd /home/user2/practice $ cd ~$ pwd / $ cd ~guest $ pwd /home/guest VÕ TẤN DŨNG Using the ls Command To determine the contents of a directory, use the ls command This command will display a listing of all files and directories within specified directories If no pathname is given as an argument, ls will display the contents of the current directory Command Format ls [-option(s)] [pathname[s]] Example: $ cd $ pwd /home/user2 $ ls dante dir1 dir3 file1 file3 practice dante_1 dir2 dir4 file2 file4 $ls dir1 coffees fruit trees $ ls /var/mail user1 user2 user3 user4 user5 VÕ TẤN DŨNG Displaying Hidden Files • File names that begin with a dot (.) are called hidden files They are not shown by default because they are infrequently edited • Use ls -a to list all files in a directory, including hidden (.) files Example: $ pwd /home/user2 $ ls -a kshrc dante1 dir2 dir4 file2 file4 dante dir1 dir3 file1 file3 practice $ VÕ TẤN DŨNG Displaying File Types • Use ls -F to display file types The various file types are displayed using the following symbols: Showing File Type: $ ls -F /etc cron@ asppp.cf* shadow uucp/ $ VÕ TẤN DŨNG Displaying a Long Listing • To see detailed information about the contents of a directory use the ls -l command VÕ TẤN DŨNG Displaying a Long Listing (cont.) VÕ TẤN DŨNG Listing Individual Directories • Use ls -ld to display detailed information about a directory, but not its contents This is useful when you want to see the permissions on a directory and not the information about its contents VÕ TẤN DŨNG Displaying a Recursive Listing • Use ls -R to display the contents of a directory and all of its subdirectories VÕ TẤN DŨNG Meta-characters • Metacharacters are keyboard characters with special meaning to the shell A general definition of a meta character is any keyboard character that is not alphanumeric • for example: • It is very important not to use meta characters when naming files and directories The dot (.) and underscore ( _ ) are the only two non-alphanumeric characters that are not metacharacters This is why you can use the dot (.) and the underscore ( _ ) in file names A hyphen (-), even though it is a metacharacter (used to delineate options in a command line), can also be used in file names VÕ TẤN DŨNG Asterisk • The asterisk (*) represents zero or more characters, except the leading dot on a hidden file The asterisk is often referred to as a wildcard character Example: $ ls dante dir1 dir3 file1 file3 fruit practice dante_1 dir2 dir4 file2 file4 fruit2 $ ls d* dante dante_1 dir1: coffees fruit trees dir2: beans notes recipes dir3: planets dir4: flowers VÕ TẤN DŨNG Question Mark • The question mark (?) matches any single character, except for the leading dot on a hidden file Example: $ ls dante dir1 dir3 file1 file3 fruit practice dante_1 dir2 dir4 file2 file4 fruit2 $ ls dir? dir1: coffees fruit trees dir2: beans notes recipes dir3: planets dir4: flowers VÕ TẤN DŨNG Question Mark (cont.) • The following example illustrates the message you will receive if no file name matches the wildcard character: Example: $ ls z? z?: No such file or directory $ VÕ TẤN DŨNG Square Brackets • Use square brackets ([ ]) to match a set or range of characters for a single character position The characters inside the brackets not generally need to be in any order; for example, [abc] is the same as [cab] However, if you are looking for a range of characters, they must be in proper order (for example, [a–z] or [3–9]) If you want to search for all alphabetic characters, whether lowercase or uppercase, use [A–z] for the pattern to match You can use alphabetic or numeric characters for the search pattern Example: $ ls [b-f]* dante dir1 dir3 file1 file3 fruit practice dante_1 dir2 dir4 file2 file4 fruit2 $ $ ls [af]* file1 file2 file3 file4 fruit fruit2 $ VÕ TẤN DŨNG Semicolon • The semicolon (;) enables you to enter multiple commands on a single command line The semicolon is also referred to as the command separator Command Format Command ; command Example: $ cd;ls dante dir1 dir3 file1 file3 fruit practice dante_1 dir2 dir4 file2 file4 fruit2 $ date;cal;pwd Sun Jul 18 11:05:39 MDT 1999 July 1999 S M Tu W Th F S 123 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 /home/user2 VÕ TẤN DŨNG END OF UNIT • remember to your homework (see http://sites.google.com/site/votandungsg/) VÕ TẤN DŨNG ... ls -F /etc cron@ asppp.cf* shadow uucp/ $ VÕ TẤN DŨNG Displaying a Long Listing • To see detailed information about the contents of a directory use the ls -l command VÕ TẤN DŨNG... information about its contents VÕ TẤN DŨNG Displaying a Recursive Listing • Use ls -R to display the contents of a directory and all of its subdirectories VÕ TẤN DŨNG Meta-characters • Metacharacters... location VÕ TẤN DŨNG Absolute Pathname - An absolute pathname specifies a file or directory in relation to the entire Linux file hierarchy The hierarchy begins at the / (root) directory - Absolute