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Day 2 of 5
⏱ ~60 minutes
Linux in 5 Days — Day 2

Files: Reading, Writing, Searching

Read files with cat/less, edit with nano, search with grep and find, and chain commands with pipes.

Reading Files

Reading commands
cat file.txt           # print entire file
less file.txt          # paginated view (q to quit)
head -n 20 file.txt    # first 20 lines
tail -n 20 file.txt    # last 20 lines
tail -f /var/log/syslog  # follow in real-time
Editing with nano
nano file.txt
# Ctrl+O = save
# Ctrl+X = exit
# Ctrl+W = search
# Ctrl+K = cut line
# Ctrl+U = paste
grep: Search File Content
grep 'error' app.log                    # lines containing 'error'
grep -i 'error' app.log                 # case-insensitive
grep -r 'TODO' ./src/                   # recursive search
grep -n 'error' app.log                 # show line numbers
grep -v 'DEBUG' app.log                 # lines NOT matching
grep -E 'error|warning' app.log         # regex: error OR warning
grep -c 'error' app.log                 # count matching lines
find: Search for Files
find . -name '*.txt'                     # by name
find . -name '*.log' -newer config.txt   # modified after
find /var/log -size +10M                 # files over 10MB
find . -type f -name '*.py' -exec grep -l 'import os' {} \;
Pipes: Chain Commands
# | passes output of one command as input to the next
cat app.log | grep 'error' | wc -l      # count error lines
ls -la | sort -k5 -n                     # sort by file size
ps aux | grep nginx                      # find nginx processes
cat /etc/passwd | cut -d: -f1 | sort    # list usernames, sorted
📝 Day 2 Exercise
Search Logs
  1. D
  2. o
  3. w
  4. n
  5. l
  6. o
  7. a
  8. d
  10. a
  12. s
  13. a
  14. m
  15. p
  16. l
  17. e
  19. l
  20. o
  21. g
  23. f
  24. i
  25. l
  26. e
  28. (
  29. o
  30. r
  32. u
  33. s
  34. e
  36. /
  37. v
  38. a
  39. r
  40. /
  41. l
  42. o
  43. g
  44. /
  45. s
  46. y
  47. s
  48. l
  49. o
  50. g
  51. )
  52. .
  54. F
  55. i
  56. n
  57. d
  59. a
  60. l
  61. l
  63. e
  64. r
  65. r
  66. o
  67. r
  69. l
  70. i
  71. n
  72. e
  73. s
  74. .
  76. C
  77. o
  78. u
  79. n
  80. t
  82. t
  83. h
  84. e
  85. m
  86. .
  88. F
  89. i
  90. n
  91. d
  93. u
  94. n
  95. i
  96. q
  97. u
  98. e
  100. I
  101. P
  103. a
  104. d
  105. d
  106. r
  107. e
  108. s
  109. s
  110. e
  111. s
  113. i
  114. n
  116. a
  117. n
  119. n
  120. g
  121. i
  122. n
  123. x
  125. a
  126. c
  127. c
  128. e
  129. s
  130. s
  132. l
  133. o
  134. g
  135. .
  137. U
  138. s
  139. e
  141. f
  142. i
  143. n
  144. d
  146. t
  147. o
  149. l
  150. o
  151. c
  152. a
  153. t
  154. e
  156. a
  157. l
  158. l
  160. .
  161. c
  162. o
  163. n
  164. f
  166. f
  167. i
  168. l
  169. e
  170. s
  172. i
  173. n
  175. /
  176. e
  177. t
  178. c
  179. .

Day 2 Summary

  • cat for quick reads, less for long files, tail -f for live logs.
  • grep -r 'pattern' dir/ searches recursively through all files in a directory.
  • Pipes | are the Unix superpower: chain simple tools into complex operations.
  • find . -name '*.txt' finds files. Add -exec command {} \; to act on each result.
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Day 1: The Terminal and File System
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Day 3: Permissions and Users
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