![Meta characters can be used with ls command as
follows:
• $ls *t : list all files ending with the letter t.
• $ls p* : list all files starting with the letter p.
• $ls ?at : list all three letter file names ending with
‘at’ and starting with any character.
• $ls [abc]* : list all files starting with the letters a, b
or c.
• $ls [!abc]* : list all file names which do not start
with the alphabets a, b or c
• $ls / : lists the contents of the root directory](https://image.slidesharecdn.com/2-240302142401-c372e010/85/2-UNIX-OS-System-Architecture-easy-pptx-30-320.jpg)
2. UNIX OS System Architecture easy.pptx
- 1. UNIX System Architecture Hardware Kernel Shell Tools and Applications
- 3. Kernel • Core of the operating system • Collection of programs and sub routines written in C • Is in direct control of the underlying hardware Functions include: 1. File management 2. Process management 3. Memory management 4. Converting data from user level to machine level. 5. CPU scheduling 6. Dealing with interrupts from hardware devices.
- 4. Shells and GUIs • Shell acts as a command interpreter, which interprets the user commands and transfers them to the kernel for execution • Performs as an interface between the user and the kernel. • Only one kernel and there can be several shells running in the memory, one for every logged – in user. • Shell invokes a command line prompt (for ex: $), where the user can type a UNIX command.
- 5. Types of shells 1. Bourne shell 2. C shell 3. Korn shell 4. Bourne – again shell Bourne shell • Most common shell distributed with UNIX system. • Is named after its author Stephen Bourne • Most widely used shell • Executable filename is sh
- 6. C shell • Developed by Bill Joy • Coding is similar to C programming language • Shell scripts of this will not work with Bourne shell • Major advantage over Bourne shell is its ability to execute processes in the background. • Executable file is csh • TC shell(tcsh) is a free version of C shell under Linux
- 7. Korn shell • Developed by David Korn • Combines the best features of Bourne shell and C shell • One of the widely used shells • Runs Bourne shell scripts without any changes • Executable file is ksh Bourne – Again shell • Developed by Fox and C Ramey • Default shell for most Linux operating systems and its variants • Executable file is sh
- 8. File system • A major component. • Is organized in an hierarchical manner. • In UNIX, everything including hardware devices is treated as a file. • Resembles a tree structure with its root at the top. • Can be local or distributed.
- 9. System utilities and application programs • System utilities such as ls, cp, grep, bc etc. perform a single task extremely well. • System utilities provide remote network and administration services • Application programs in Linux include editor, c compiler, drawing package, Soffice (StarOffice) etc.
- 10. UNIX command format • UNIX commands can be very simple one word commands or they can take a number of additional arguments (parameters) as part of the command. • In general a UNIX command has the following general form... $command option(s) filename(s) • The command is the name of the utility or program that we are going to execute. Ex: $rm –i test1 #the command rm deletes the file test1, -i prompts before deleting file.
- 11. • The options are passed into the command to modify the way the command works. It is typical for these options to have be a hyphen followed by a single character, such as-l. • The filename is the last argument for a lot of UNIX commands. It is simply the file or files that we want the command to work on. • Take note that not all commands work on files, such as ssh which takes the name of a host as its argument. (The ssh command is used to logging into a remote host and execute commands on the remote machine.)
- 12. • The clear command, which is used to remove all previous commands and output from the display screen, is one of the rare commands that accepts neither options nor arguments.
- 13. UNIX internal and external commands • UNIX commands are classified into two types Internal Commands - Ex: cd, echo,fg External Commands - Ex: ls, cat Internal Command: • Internal commands are something which is built into the shell. • For the shell built in commands, the execution speed is really high. It is because no process needs to be generated for executing it. • For example, when using the "cd" command, no process is created. The current directory simply gets changed on executing it. External Command: • External commands are not built into the shell. • These are executables present in a separate file. • When an external command has to be executed, a new process has to be generated and the command gets executed. • For example, when you execute the "cat" command, which usually is at /usr/bin, the executable /usr/bin/cat gets executed.
- 14. Directory commands • pwd • cd • mkdir • rmdir • mv • tree
- 15. pwd - print working directory or present working directory) • Prints the absolute pathname of our current working directory • The pwd command can have options, but it doesn’t take any arguments Syntax & Ex: $pwd cd - changing the directory • Is used to move from one directory to another. • Uses a pathname (either relative or absolute) as its argument. Syntax: $cd directoryname Ex: $cd /home/harley/essays • To change to the / (root directory), use: $cd / • To return to home, use: $cd • To change to the parent directory, use: $cd .. Please note: There is a space between the command cd and its argument
- 16. mkdir – making directory • To make a directory, we use mkdir command. Syntax: $mkdir directoryname Examples: $mkdir extra $mkdir sample1 sample2 rmdir – removing directory • Removes one or more directories or sub – directories • Directories can be removed only when they are empty. Ex: $rmdir sample1
- 17. • A directory tree can be removed recursively and forcefully using the rm command with the –r and –f options mv – moving or renaming a directory • To move or rename a directory, we use mv command Syntax: $mv directory target where directory is the directory we want to move or rename and target is the target or new name Ex: $mv data extra • We use mv command to “move” a directory from one place to another. • The command mv both moves and renames.
- 18. tree • Lists the contents of directories in a tree like format. • Options –d (list directories only), -f (prints the full path prefix for each file), -p (list a tree that also shows the file permissions) Ex: $tree -p
- 19. File related commands • cat • cp • mv • rm • touch • ls • more • head • tail
- 20. cat • Is used for creating files, displaying contents of the files, concatenating files and for appending files. Creating files: • Can be used to create small files. • Takes input from keyboard and sends the output to the monitor. Ex: $cat > fruits Apple Orange Grapes <ctrl d>
- 21. Displaying contents of files • cat can be used to display the contents of the one file or more than one files Examples: $cat fruits $cat fruits vegs Concatenation of files • cat command can concatenate the contents of two or more files and store them in another file. Ex: $cat test1 test2 > test3
- 22. Append files • The cat command can be used to append or add data to the contents of the file using the symbol >> Ex: $cat >> fruits Pineapple Guava <ctrl d> • Can also be used to append the contents of one file to another file Ex: $cat fruits >> item • Options with cat command are –v (displays non – printable ASCII characters also), -n (numbers the lines in the file) etc.
- 23. cp • Can copy a file or a group of files, across directories. Syntax: $cp <source_file> <new_filename> Ex: $cp test1 test2 #creates an exact copy of test1 with file name as test2 • More than one file can be copied into another directory Ex: $cp test1 test2 testdir
- 24. cp options • -i : interactive, prompts the confirmation before overwriting the target file. • -r : is recursive copying • -p : copies the file and preserves the attributes such as owner id, group id, permissions and last modification time
- 25. mv – moving or renaming a file • To move or rename a file, we use mv command Syntax: $mv filename target Where filename indicates the file we want to move or rename and target is the target or new name Ex: $mv veg vegetables • We use mv command to “move” a file from one place to another. • The command mv both moves and renames. • A group of files can also be moved into a directory.
- 26. mv options: • -f : suppresses all prompting and forces overwriting of target file. • -i : prompts before overwriting of destination file • -p : preserves the attributes such as owner id, group id, permissions and last modification time
- 27. rm • Is used to delete one or more files • Meta characters(*,? etc.) can be used to delete files with common patterns Syntax: $rm filename Ex: $rm fruits rm options: • -f : suppresses all prompting. • -i : prompts before deleting files • -r : is recursively removes the files. (Ex: $rm –r*)
- 28. touch • Is used to create empty files Examples: $touch course1 $touch course1 course2 touch options • -a : to change the access time • -m : to change the modification time
- 29. ls • Is used to display all the files and sub directories in a current directory ls options: • -a : list all files including hidden files. • -x : list the content in a row – wise format. • -r : list the contents, sorted in a reverse alphabetical order. • -i : displays inode numbers of files • -l : display all the files and subdirectories in the long format including permissions, file type, owner id, group id etc. • -u : list the contents based on the access time or usage time.
- 30. Meta characters can be used with ls command as follows: • $ls *t : list all files ending with the letter t. • $ls p* : list all files starting with the letter p. • $ls ?at : list all three letter file names ending with ‘at’ and starting with any character. • $ls [abc]* : list all files starting with the letters a, b or c. • $ls [!abc]* : list all file names which do not start with the alphabets a, b or c • $ls / : lists the contents of the root directory
- 31. more • Is used to view the contents of a file page by page. • Takes one or more file names as arguments Ex: $more studdet.txt • The user can quit from more by typing q
- 32. head • Is used to display the first few lines of one or more files • Without any options, by default, it displays first 10 lines of the file. Examples: $head bcalist $head -4 bcalist • The head command can be used with multiple files Ex: $head -2 bcalist bsclist
- 33. tail • Is used to display the last few lines of a file. • By default, it displays the last 10 lines of the file. Examples: $tail bcalist #displays the last 10 lines $tail -4 bcalist #displays the last 4 lines $tail +7 bcalist #displays all the lines starting from the line number 7 up to end of file • The tail command cannot take multiple files
- 34. Comparing files • The commands for comparing files can be used to compare two versions of the same file. • Most common commands for comparing two files are: cmp diff comm
- 35. cmp • Is used to determine whether the two files are identical in all respects. • When files are identical, system prompt appears without any message. • When there are differences, the location of the first mismatch is echoed on the screen. Ex: $cmp bcalist bsclist
- 36. diff • It first compares the two files byte by byte, and indicates the differences. • Also tells how the contents of the first file can be changed to match the text from the second file and vice versa. Ex: $diff bcalist bsclist
- 37. comm • Compares two sorted files and shows lines that are same and those that are different. Ex: $comm bcalist bsclist
- 38. Disk related commands The df command - disk free • Reports the amount of free space available for each file system separately. Examples: $df $df -h df options: • -h : print sizes in human readable format (e.g., 1K 234M 2G) • -T : print file system type. • -a : include dummy file systems • -i : list inode information instead of block usage.
- 39. The du command – disk usage • It estimates and displays the disk space used by files. Ex: $du du options: -a : displays the space that each file is taking up -ch : displays file sizes and the total capacity of all files combined -k : reports the file sizes in units of 1024 bytes
- 40. The ulimit command – user limit • This command is used to control occupying huge amount of space by files created by users. • When applied at the command prompt ulimit displays a value which signifies the largest file that can be created by the user in the file system. Ex: $ulimit • The default value of Solaris and Linux for ulimit is unlimited.
- 41. • An ordinary user can decrease the value, but cannot increase it. • Once the limit is decreased, it remains effective till the user logs out. • A super user can use ulimit to impose restriction on the maximum file size, that a user is allowed to create. • A super user can increase or decrease the value of ulimit.