BILKENT UNIVERSITY DEPARTMENT OF COMPUTER TECHNOLOGY AND INFORMATION SYSTEMS CTIS156 INFORMATION...

BILKENT UNIVERSITYDEPARTMENT OF COMPUTER TECHNOLOGY AND

INFORMATION SYSTEMS

CTIS156 INFORMATION TECHNOLOGIES II

CHAPTER 10:

ADVANCED FILE PROCESSING

CH.10 ADVANCED FILE PROCESSING

● Objectives:– To explain how file compression is performed in Linux

– To discuss searching for commands and files in Linux file structure

– To describe searching files for expressions, strings, and patterns

– To explain command history

– To describe input/output redirection

– To explain Linux pipes

2 CTIS156 INFORMATION TECHNOLOGIES II


● 10.3 Compressing Files– Reducing the size of files:

● To save disk space● To save time when transmitting over the internet● To save time during file save

– Linux provides several commands to compress/decompress files:

● gzip command is used to compress files● gunzip command is used to decompress files



● 10.3 Compressing Files (cont)– gzip [options] [file-list]

● It saves the compressed file with a .gz extension● -f option forces compression even though .gz file

already exists● -r option recursively compresses files in the

subdirectories● -l option displays a list of compressed files,

compressed and uncompressed file sizes, compression ratio, etc.



● 10.3 Compressing Files (cont)– gunzip [options] filename

● Uncompresses the compressed files.




● 10.4 Sorting Files– Order set of items according to some criteria.– The sorting process is based on using a field, or portion

of each item, known as sort key.– The Linux sort utility can be used to sort items in text

(ASCII) files.– By default, the sort utility takes each line, starting with

the first column to be the key.



● 10.4 Sorting Files (cont)

[vural@vpdesktop vural]$ cat studentsJohn Johnsen [email protected] 503.555.1111Hassaan Sarwar [email protected] 503.444.2132David Kendal [email protected] 229.111.2013Kelly Kimberly [email protected] 555.123.9999Maham Sarwar [email protected] 713.888.0000




[vural@vpdesktop vural]$ sort studentsDavid Kendal [email protected] 229.111.2013Hassaan Sarwar [email protected] 503.444.2132John Johnsen [email protected] 503.555.1111Kelly Kimberly [email protected] 555.123.9999Maham Sarwar [email protected] 713.888.0000




[vural@vpdesktop vural]$ sort +1 studentsJohn Johnsen [email protected] 503.555.1111David Kendal [email protected] 229.111.2013Kelly Kimberly [email protected] 555.123.9999Hassaan Sarwar [email protected] 503.444.2132Maham Sarwar [email protected] 713.888.0000




[vural@vpdesktop vural]$ sort +3 studentsDavid Kendal [email protected] 229.111.2013Hassaan Sarwar [email protected] 503.444.2132John Johnsen [email protected] 503.555.1111Kelly Kimberly [email protected] 555.123.9999Maham Sarwar [email protected] 713.888.0000




[vural@vpdesktop vural]$ sort -r studentsMaham Sarwar [email protected] 713.888.0000Kelly Kimberly [email protected] 555.123.9999John Johnsen [email protected] 503.555.1111Hassaan Sarwar [email protected] 503.444.2132David Kendal [email protected] 229.111.2013


● Searching For Commands and Files:– find directory-list expression

● Searches for the files that match the criteria defined by the

expression in the directory-list

● Searches the directories recursively

● Expression examples:

– -name pattern (for files that match pattern)

– -newer file (for files newer than the file)

– -user username (for files owned by a specific user)

– -print (displays the pathnames of the files found)



● Searching For Commands and Files (cont):– Examples of find command:

● find ~ -name vural.c –print● find / -name profile –print● find /usr –name socket.h –print● find . –user ctis -print



● Searching For Commands and Files (cont):– whereis [options] [file-list]

● It searches and displays the location of a command’s files (executable, source and man pages)

● Example:

– whereis ls

– which [command-list]● If there are more than one version of a command file, then it

displays the absolute pathname of the command executed by the shell.



● Searching a text in the text files:– grep [options] pattern [file-list]

● It searches the pattern (a string) inside the text files in the file-list and if finds, displays the lines that has

● -n (display the line numbers in the output)

● -l (display only the filenames that contain the string)

● Examples:

– grep umask /etc/profile

– grep include *.c



● Command History:– history [options] [filename]

● Displays the command history

● The command history is stored in a file ~/.bash_history

● If a number is specified as an option, the command displays only the last number of commands

● !! (executes the last command in the history list)

● !n (executes the command in line n of the history list)


CH.12 REDIRECTION AND PIPING

● 12.1 Introduction:– Most commands and programs perform the following

operations:● Input● Processing● Output

– Questions:● Where does a program take it's input?● Where does it send it's output● Where are the error messages displayed?



● 12.2 Standard Files:– By default, three standard files are opened automatically by

the kernel for every command or program executed:● stdin (keyboard): Where it takes input● stdout (screen): Where it sends output● stderr (screen): Where it sends the error messages



● 12.3 Input Redirection:– The < (less than) symbol is used to change the standard

input. The syntax is:

– command < input-file– The command takes its input from another file, instead of stdin (keyboard)



● Input Redirection example:

- bc is a calculator program in Unix, takes the input form the keyboard by default.

- We can write the input to a file and use input redirection$ bc2+24$ cat bc_input2+2$ bc < bc_input4



● 12.4 Output Redirection:– The > (greater than) symbol is used to change the standard

output. The syntax is:

– command > output-file– The command write its output to an external file instead of

the standard output (screen)



● Output Redirection example:$ ls -l > ls.file$ cat ls.filetotal 30drwx--x--x 8 vpolat ctisac 1536 Apr 20 10:55 .drwxr-xr-x 29 root other 512 Feb 2 12:07 ..-rw-r--r-- 1 vpolat ctisac 53 Feb 28 10:57 .profile-rw------- 1 vpolat ctisac 2748 Apr 20 10:55 .sh_historydrwxr-xr-x 2 vpolat ctisac 512 Apr 16 2004 _fpclassdrwxr-xr-x 3 vpolat ctisac 512 Sep 23 2004 _privatedrwxr-xr-x 3 vpolat ctisac 512 Apr 16 2004 _themes-rw-r--r-- 1 vpolat ctisac 4 Apr 20 10:44 bc_inputdrwxr-xr-x 2 vpolat ctisac 512 Sep 12 2005 images-rw-r--r-- 1 vpolat ctisac 0 Apr 20 10:55 ls.filedrwx------ 2 vpolat ctisac 512 Jul 20 2004 maildrwxr-xr-x 7 vpolat ctisac 1536 Mar 23 09:30 public_html



● 12.5 Combining Input and Output Redirection:

Command < input-file > output-fileCommand > output-file < input-file

Example:


$ cat bc_input2+2$ bc < bc_input > bc_output$ cat bc_output4


● 12.7 Redirecting Standard Error:– The 2> (2 greater than) symbol is used to change the

standard error file. The syntax is:

– command 2> error-file– The error messages are written into an external file instead

of the stderr (screen)



● 12.9 Redirecting stdin stdout and stderr in one command:

● 0< standard input● 1> standard output● 2> standard error

Example:● $sort 0< students 1> students.sorted 2> sort.error



● 12.11 Linux Pipes:– In Linux stdout of a command can be connected to the stdin of another command.

– | (pipe) character is used between the commands

– Syntax:● command1 | command2 |...| commandN



● Linux Pipes (cont):– Linux pipe example:

● $ls -l | more

– The output of ls -l command is fed to more command as input

● $history | tail -7

– The output of history command is fed to tail -7 command as input



● References:● LINUX: The Textbook. Sarwar, Koretsky, Sarwar.

Addison Wesley. 2002.


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