Day 2

Commands

16 :/pattern 17. :%s/Testing/development/g 18. :1 s/Testing/dev/g 19. :5,$ s/Testing/dev/g 20. 1,5 s/Testing/dev/g

1. mkdir -p dir1/dir2/dir3/Users/apple/Documents/Devops/Ref class Notes/linux Devops-class-13-May-2022.txt

2. wc filename

3. wc -l f1

4. wc -w f1

5. wc -c f1

6. wc -m f1

7. echo "statement"

8. echo -e "Hi \nThis is devops class \nThird line"

9. [Redirect]

10. [Append]

11. du filename

12. du -sh filename

13. du -sh directory_name

14. du -sh *

15. head filename

16. head -3 f1

17. head -20 f1

18. tail f1

19. tail -2 f1

20. tail -20 f1

21. | [pipe]

22. ls -l|wc -l

23. head -10 file|tail -1

24. grep

25. grep -i "devops" f1

26. grep -in "pattern" filename

27. grep -ic "pattern" filename

28. grep -iw "devops" f1

29. grep -li "devops" *

30. grep -ilr "devops" *

31. grep -ie "devops" -e "teams" f1

32. head -8 f1|tail -1|wc -w

33. df -h

34. free -g

Vi/Vim Editor Commands

16. :/pattern

Purpose: Search for a pattern in the current file within Vim editor. Usage: /pattern searches forward from the current cursor position for the first occurrence of "pattern". Example: :/devops will find the first occurrence of "devops" in the file. Navigation:

• Press n to go to the next occurrence

• Press N to go to the previous occurrence

17. :%s/Testing/development/g

Purpose: Replace all occurrences of "Testing" with "development" across the entire file. Breakdown:

• % = Apply to all lines in the file

• s = Substitute command

• /Testing/ = Find pattern

• /development/ = Replace pattern

• g = Global flag (replace all occurrences on each line) Example: If file has "Testing is important. Testing is critical." it becomes "development is important. development is critical."

18. :1 s/Testing/dev/g

Purpose: Replace all occurrences of "Testing" with "dev" on line 1 only. Breakdown:

• :1 = Target line 1

• s/Testing/dev/ = Substitute command

• g = Replace all occurrences on that line Example: On line 1, "Testing Testing code" becomes "dev dev code"

19. :5,$ s/Testing/dev/g

Purpose: Replace all occurrences of "Testing" with "dev" from line 5 to the end of the file. Breakdown:

• :5,$ = Line 5 to end of file ($ represents last line)

• s/Testing/dev/ = Substitute command

• g = Replace all occurrences on each line in the range Example: All lines from 5 onwards have "Testing" replaced with "dev"

20. 1,5 s/Testing/dev/g

Purpose: Replace all occurrences of "Testing" with "dev" from line 1 to line 5. Breakdown:

• 1,5 = Lines 1 through 5

• s/Testing/dev/ = Substitute command

• g = Replace all occurrences on each line Example: Only the first 5 lines are affected by the replacement

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Directory and File Creation

21. mkdir -p dir1/dir2/dir3/Users/apple/Documents/Devops/Ref class Notes/linux Devops-class-13-May-2022.txt

Purpose: Create a nested directory structure, creating parent directories as needed. Note: The .txt file is actually part of the directory path (not a file). Breakdown:

• mkdir = Make directory command

• -p = Parent flag (creates all intermediate directories if they don't exist)

• Path creates: dir1/dir2/dir3/Users/apple/Documents/Devops/Ref class Notes/linux Devops-class-13-May-2022.txt as a directory Important: Without -p, this command would fail if parent directories don't exist. With -p, all missing parent directories are automatically created. Example: Creates the entire hierarchy in one command instead of creating each level separately.

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Word Count Command (wc)

22. wc filename

Purpose: Display the number of lines, words, and bytes in a file. Output Format: [lines] [words] [bytes] filename Example Output: 10 50 250 filename

23. wc -l f1

Purpose: Count and display only the number of lines in file f1. Breakdown: -l = Lines only flag Example Output: 42 f1 (means the file has 42 lines)

24. wc -w f1

Purpose: Count and display only the number of words in file f1. Breakdown: -w = Words only flag Example Output: 156 f1 (means the file has 156 words)

25. wc -c f1

Purpose: Count and display only the number of bytes in file f1. Breakdown: -c = Bytes only flag Example Output: 1024 f1 (means the file is 1024 bytes)

26. wc -m f1

Purpose: Count and display only the number of characters in file f1. Breakdown: -m = Characters only flag Note: Unlike -c (bytes), -m counts actual characters (important for multi-byte UTF-8 characters) Example Output: 950 f1 (means the file has 950 characters)

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Echo Command

27. echo "statement"

Purpose: Print the text "statement" to standard output (terminal). Output: statement Usage: Commonly used to display messages, variables, or create file content in scripts.

28. echo -e "Hi \nThis is devops class \nThird line"

Purpose: Print text with escape sequences interpreted (newlines will be actual line breaks). Breakdown:

• -e = Enable interpretation of backslash escapes

• \n = Newline character Output:

Hi
This is devops class
Third line

Without -e: Would print literally as Hi \nThis is devops class \nThird line

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Input/Output Redirection

29. > [Redirect]

Purpose: Redirect standard output to a file, overwriting the file if it exists. Example: echo "Hello" > output.txt creates output.txt with content "Hello" Important: Overwrites existing file content without warning. Usage: command > filename

30. >> [Append]

Purpose: Redirect standard output to a file, appending to existing content (does not overwrite). Example: echo "New line" >> output.txt adds "New line" to the end of output.txt Important: Preserves existing file content and adds new content at the end. Usage: command >> filename

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Disk Usage Command (du)

31. du filename

Purpose: Display disk usage of a specific file in disk blocks (usually 512 bytes per block). Output Example: 8 filename (means 8 blocks, approximately 4KB) Note: For files, du shows allocated disk space, not logical file size.

32. du -sh filename

Purpose: Display human-readable disk usage of a file in a simplified format. Breakdown:

• -s = Summary (total size only, not details)

• -h = Human-readable (shows K, M, G, T for kilobytes, megabytes, gigabytes, terabytes) Output Example: 2.5M filename

33. du -sh directory_name

Purpose: Display total human-readable disk usage of a directory and all its contents. Breakdown:

• -s = Summary of the entire directory

• -h = Human-readable format Output Example: 1.2G directory_name

34. du -sh *

Purpose: Display human-readable disk usage of all files and directories in the current directory. Breakdown:

• -s = Summary for each item

• -h = Human-readable format

• * = All items in current directory Output Example:

4.2K file1.txt
2.1M directory1
512K file2.txt

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Head Command

35. head filename

Purpose: Display the first 10 lines of a file (default behavior). Example: Shows the beginning of a file for quick preview.

36. head -3 f1

Purpose: Display the first 3 lines of file f1. Breakdown: -3 specifies the number of lines to display Example Output: First 3 lines of the file appear

37. head -20 f1

Purpose: Display the first 20 lines of file f1. Breakdown: -20 specifies display of first 20 lines Example Output: First 20 lines of the file appear

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Tail Command

38. tail f1

Purpose: Display the last 10 lines of file f1 (default behavior). Example: Shows the end of a file for quick preview.

39. tail -2 f1

Purpose: Display the last 2 lines of file f1. Breakdown: -2 specifies the number of lines to display from the end Example Output: Last 2 lines of the file appear

40. tail -20 f1

Purpose: Display the last 20 lines of file f1. Breakdown: -20 specifies display of last 20 lines Example Output: Last 20 lines of the file appear

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Pipe Operator

41. | [pipe]

Purpose: Connect the output of one command as input to another command. Usage: command1 | command2 Benefit: Allows chaining multiple commands together for complex operations. Example: cat file | wc -l (shows content of file and counts lines)

42. ls -l|wc -l

Purpose: List files in detailed format and count the number of lines in the output. Breakdown:

• ls -l = Long format listing of files

• | = Pipe the output to the next command

• wc -l = Count lines in the piped output Result: Shows total number of files/directories (including header line) in current directory Output Example: 15 (means 14 items plus 1 header line)

43. head -10 file|tail -1

Purpose: Display only the 10th line of a file. Breakdown:

• head -10 file = First 10 lines of the file

• | = Pipe to the next command

• tail -1 = Last line of the piped output (which is the 10th line) Result: Shows exactly the 10th line of the file Use Case: Extracting a specific line from the middle of a file

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Grep Command

44. grep

Purpose: Search for lines containing a specific pattern in a file or input. Basic Usage: grep "pattern" filename Output: All lines that contain the pattern Example: grep "error" logfile.txt shows all lines containing "error"

45. grep -i "devops" f1

Purpose: Search for "devops" in file f1, case-insensitive. Breakdown: -i = Ignore case (matches "devops", "DEVOPS", "DevOps", etc.) Output: All lines containing "devops" regardless of case Example: Finds "DEVOPS Engineer" and "devops class" with same command

46. grep -in "pattern" filename

Purpose: Search for "pattern" in filename, case-insensitive, and show line numbers. Breakdown:

• -i = Ignore case

• -n = Print line numbers Output Format: [line_number]:[matching_line] Example Output: 5:This is a pattern line (pattern found on line 5)

47. grep -ic "pattern" filename

Purpose: Count how many lines contain the pattern (case-insensitive). Breakdown:

• -i = Ignore case

• -c = Count matching lines Output: Just the count number Example Output: 7 (7 lines contain the pattern)

48. grep -iw "devops" f1

Purpose: Search for "devops" as a whole word only, case-insensitive. Breakdown: -w = Word boundaries (won't match "devopsclass" or "mydevops") Output: Lines containing "devops" as a complete word Difference: Without -w, "devops" in "devopsclass" would match; with -w, it won't

49. grep -li "devops" *

Purpose: List filenames containing "devops" (case-insensitive) from all files in current directory. Breakdown:

• -l = List filenames only (not the matching lines)

• -i = Ignore case

• * = All files in current directory Output: Filenames that contain the pattern Example Output:

file1.txt
file3.txt
notes.md

50. grep -ilr "devops" *

Purpose: Recursively search all files in current directory and subdirectories for "devops", listing matching filenames. Breakdown:

• -i = Ignore case

• -l = List filenames only

• -r = Recursive (search subdirectories)

• * = Start from current directory Output: Filenames from all directories containing the pattern Use Case: Finding files across entire project/directory tree

51. grep -ie "devops" -e "teams" f1

Purpose: Search for lines containing either "devops" OR "teams" in file f1. Breakdown:

• -i = Ignore case

• -e "devops" = First pattern to match

• -e "teams" = Second pattern to match Output: All lines matching either pattern Example: A line with "devops class" OR "teams collaboration" would both match Use Case: Searching for multiple alternative patterns

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Complex Pipeline Commands

52. head -8 f1|tail -1|wc -w

Purpose: Count the number of words on the 8th line of file f1. Breakdown:

• head -8 f1 = Get first 8 lines

• |tail -1 = Get the last line of those (which is line 8)

• |wc -w = Count words in that line Result: Shows word count of exactly the 8th line Output Example: 5 (the 8th line has 5 words) Use Case: Extracting and analyzing specific lines

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System Information Commands

53. df -h

Purpose: Display disk space usage of all mounted filesystems in human-readable format. Breakdown:

• df = Disk free (shows filesystem usage)

• -h = Human-readable (shows K, M, G, T) Output Columns: Filesystem, Size, Used, Available, Use%, Mount point Example Output:

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       50G   30G   20G  60%  /
/dev/sda2      100G   50G   50G  50%  /home
tmpfs           8.0G    0  8.0G   0%  /dev/shm

Use Case: Checking available disk space before large operations

54. free -g

Purpose: Display memory (RAM) usage in gigabytes. Breakdown:

• free = Show free and used memory

• -g = Display in gigabytes (alternative: -m for megabytes, -h for human-readable) Output Columns: Total, Used, Free, Shared, Buffer/Cache, Available Example Output:

              total   used   free  shared  buffers  available
Mem:             16      8      8       1        2          6
Swap:             4      0      4       0        0          4

Use Case: Monitoring system memory availability and usage

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Summary Table

Command	Purpose	Key Flags
/pattern	Search in Vim	n/N to navigate
:%s/old/new/g	Replace all in file	g = global
wc	Word/line/byte count	-l, -w, -c, -m
echo	Print text	-e for escapes
>	Redirect (overwrite)	Creates new file
>>	Append to file	Preserves content
du	Disk usage	-sh for human-readable
head/tail	Show beginning/end	-n for line count
grep	Pattern search	-i, -n, -c, -w, -r, -l
df	Filesystem usage	-h for human-readable
free	Memory usage	-g, -m, -h