File Processing Commands Worksheet Pos 420 Version 91 Univer

File Processing Commands Worksheetpos420 Version 91university Of Phoe

File Processing Commands Worksheet – 15 Marks – Week . How do you know how many number of users currently logged into the system? (Not considering if any user is logged more than one time) (1) A. who | uniq | sort | wc -l B. who | cut -d' ' –f1 | uniq | wc -l C. who | sort | uniq | wc -l D. who | cut -d' ' –f1 | sort -u | wc -l E. who | cut -d' ' –f1 | uniq -d | wc -l Ans: 2. Create a file “employees.txt” using vi editor or pico. (The file will have 6 fields, ID, Name, Designation, Dept, D.O.B, Salary separated by pipe) Enter these lines in the file and save it. 2133|charles smith |Manager|sales|12/12/56| Rob Thomson|director |production|03/12/50||David Blake |General Manager|marketing |04/19/43| |Rick Martin|director|personnel |05/11/47|120000 (Use cut command for the following questions A,B) A. Display the person's name, his designation and salary in the above file. (Show the command and output) Ans: B. Display first 20 characters on each line in the above file. (Show the command and output) Ans: 3. How do you display the hour and minute from date command using cut utility (1) (Show the command and output) Ans: 4. What is the difference between the following commands? (1) $ who | grep 'mary' and $ who | grep '^mary' Ans: 5. We know that all user information is stored in /etc/passwd where fields are delimited by a colon. Display only their userids using cut command. (userid is the first field in /etc/passwd file) Show only top 10 userids. (1) (Show the command and output) Ans: 6. Create the following four files chapter1, chapter2, chapter3, chapter4 in your current directory and enter the following text: Chapter1 : This is the first line in this file This chapter deals with the basic information of a UNIX system. Chapter2 : This is the first line in this file This chapter deals with Unix System info and shell introduction. Chapter3 : This is the first line in this File System This chapter deals with various Unix Systems. Chapter4 : This is the first line in this file This chapter deals with kernel system. The question is to search for a string "System" or "system" in the above files. Use wild cards in both pattern and file searching. (1) (Show the command and output) Ans: 7. Show these commands and output: A. Redirect man pages of ‘grep’ to a file called, man_grep in /tmp directory. B. Display lines not having the word “system” in the above file.(1) Ans: 8. Which command of the following is correct ? (Some may work but does not make sense). (1) a. cat file file > file3 | wc -l b. cut -d ":" filename c. ls -l | grep unix myfile d. head filename | tail e. find name "myfile.txt" -print 9. We know that ls -l command shows all the files in the current directory. How do you display only the directories, not files in the current directory. (You have to use ls command, but not find command) (1) Ans: 10. How do you set only read permissions to user, group and others in octal mode for a file "myfile.txt" ? (1) Ans: 11. You observed that some of your group members are fiddling with your file "myfile" and you wanted to remove the read permission to your group. How do you do? (1) Ans: 12. Here is the long listing of a file. -rw-rw-rw- 2 Y435678 odms 22 Sep 02 12:03 myfile.txt Is the above a file or a directory? To which group does it belong? (1) Regular file, Y435678 file, Y435678 file, odms directory, odms directory, Y435678 Ans : 13. Here is another long listing of a file. (1) -rw-r----- 1 Y435678 odms 20 Sep 02 17:03 file.txt. What are the owner permissions? read, execute read, write write, execute all since s/he is the owner Ans: 14. The file users_data has the following contents : (1) Tom Smith 7..00 Rob Sheryl 8..00 Ken Bradman 7..00 Peter Smith 6..00 Dennis Smith 8..00 Tom Dave 9..00 How do you sort the above file and redirect the output to another file called sortedusers? Ans : 15. How do you list only duplicate lines in a file "myfile"? (1) Ans :

Paper For Above instruction

The following comprehensive guide addresses essential Unix/Linux shell commands and procedures aligned with the File Processing Commands Worksheet. This document aims to elucidate methods to monitor system users, manipulate text files, extract specific information, and manage permissions, thereby enhancing proficiency in Unix/Linux system administration and scripting.

1. Counting Logged-in Users

To determine the number of current users logged into a Unix/Linux system, the command `who` can be combined with text processing utilities. Among the options, the most accurate approach is: who | cut -d' ' -f1 | uniq | wc -l. This pipeline extracts usernames, removes duplicates (as a user may log in multiple times), and counts distinct users. Consequently, the correct answer is option B, which filters only unique user names and counts them.

2. Creating and Using a Text File with User Data

Constructing the file employees.txt with specific fields separated by pipes involves using a text editor such as vi or pico, inputting the data, and saving it appropriately. The six fields include ID, Name, Designation, Department, Date of Birth, and Salary. For subsequent tasks, the cut command extracts specific columns based on delimiters.

3. Displaying Name, Designation, and Salary

To display specific fields, the command uses cut with the delimiter set to '|'. For example, cut -d'|' -f2,3,6 employees.txt will output the Name, Designation, and Salary fields for all records. The output corresponds to the data extracted from the file based on the specified fields.

4. Displaying the First 20 Characters per Line

The command cut -c1-20 employees.txt displays the first twenty characters of each line in the file, allowing a quick overview of data snippets.

5. Extracting Hour and Minute from Date

Using the date command combined with cut, e.g., date +"%H:%M", directly displays current time in hours and minutes. Alternatively, if a date string is available, pipe it to cut with appropriate delimiters to extract the hour and minute parts.

6. Comparing who | grep 'mary' vs. who | grep '^mary'

The command who | grep 'mary' searches for all lines containing the sequence 'mary', regardless of position. In contrast, who | grep '^mary' restricts matches to lines where 'mary' appears at the beginning, ensuring a more precise search for usernames starting with 'mary'.

7. Displaying User IDs from /etc/passwd

To extract user IDs (the first field), the command cut -d':' -f1 /etc/passwd | head -10 outputs the first ten userIDs from the '/etc/passwd' file, demonstrating field-based extraction.

8. Searching for a String in Multiple Files

Searching for 'System' or 'system' across multiple files can be performed using wildcards. For example, grep -i 'system' chapter* searches case-insensitively in files starting with 'chapter'.

9. Saving Man Pages and Filtering Lines

Redirecting the manual pages of 'grep' to a file involves: man grep > /tmp/man_grep. To display lines from 'man_grep' that do not contain 'system', use: grep -v 'system' /tmp/man_grep.

10. Validating Commands

Among the options, valid commands include: cut -d ':' -f1 filename for extracting fields, and ls -l | grep unix filters files with 'unix' in their details. Some options like 'cat file file > file3 | wc -l' are syntactically incorrect or produce unexpected results.

11. Displaying Only Directories in Current Directory

Using the ls -l | grep '^d' command filters directory entries because directories have a 'd' at the beginning of their permission string.

12. Setting File Permissions to Read Only

To assign read permissions only to user, group, and others, in octal mode, use: chmod 444 myfile.txt.

13. Modifying Permissions to Remove Group Read Permission

To revoke read permission for the group, execute: chmod g-r myfile.

14. Determining File or Directory and Group Ownership

From the listing -rw-rw-rw- 2 Y435678 odms 22 Sep 02 12:03 myfile.txt, it's a file belonging to the 'odms' group. The presence of '-' at the start indicates a regular file.

15. Analyzing Permissions for a File

For -rw-r----- 1 Y435678 odms 20 Sep 02 17:03 file.txt, the owner has read and write permissions, indicating 'r' and 'w'. The permissions suggest the owner can read and modify the file, but no execute permission is granted.

16. Sorting File Contents and Redirecting Output

To sort the 'users_data' file and redirect output, use: sort users_data > sortedusers.

17. Finding Duplicate Lines in a File

To list only duplicate lines in 'myfile', the command is: sort myfile | uniq -d.

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