Linux Commands for Beginners 15 - Bash History — Transcript

Full transcript

1. 0:00[Music]
2. 0:19hey guys welcome to another video in my
3. 0:22Linux commands for beginner series and
4. 0:24in this video I wanted to give you guys
5. 0:27a quick look at history it's a pretty
6. 0:30easy concept but it's actually a very
7. 0:33important one that as a Linux
8. 0:35administrator you're going to be using
9. 0:37every single day so let's go ahead and
10. 0:39get started so here on my terminal
11. 0:41you've probably seen me several times in
12. 0:44previous videos using the up and down
13. 0:46arrow to basically go through previous
14. 0:49commands that we've run and that's great
15. 0:52because if you want to basically act you
16. 0:54know enter a command again you don't
17. 0:55really have to type the entire thing you
18. 0:58could just simply find it and then press
19. 1:00Enter and you know you're able to
20. 1:02execute that obviously it took me longer
21. 1:04to find the groups command than it would
22. 1:05have taken me to you know type that out
23. 1:07but sometimes you have very long
24. 1:09commands that you want to reenter so
25. 1:12going up and down in the history of
26. 1:14course is going to be a lot easier when
27. 1:17you find the command than retyping it
28. 1:18sometimes but that's really not the
29. 1:20extent of history it goes a lot more
30. 1:23than that in fact you can use the
31. 1:25history command and press Enter and you
32. 1:28can see all kinds of different things
33. 1:30here now this is my personal laptop here
34. 1:31so what you're going to see is a lot of
35. 1:34the commands that we have been using for
36. 1:36the videos that we've been doing in this
37. 1:39series and there's quite a few commands
38. 1:41right here and we can execute any one of
39. 1:44these commands at any time we don't
40. 1:47actually need to go up and down through
41. 1:49the history to find it if we just type
42. 1:52the history command by itself we can
43. 1:53actually just scroll through here and
44. 1:55find the commands we want but that's not
45. 1:57all we can do
46. 1:58notice that command that er actually
47. 2:01each one of these has a number on the
48. 2:04left hand side and we can execute that
49. 2:06command and refer to it by number which
50. 2:09is actually a really useful thing to do
51. 2:12so how do we do that well remember this
52. 2:15command is command number five nine four
53. 2:18and the command was executed was here
54. 2:21now I have customized my shell a little
55. 2:23bit so you might have the output
56. 2:25presented a little bit differently on
57. 2:27your end
58. 2:28but the main important thing is the
59. 2:29number and then the command which you
60. 2:32should have
61. 2:33so that was command 594 so I'll clear
62. 2:36the screen now we need to run command
63. 2:39594 but we can't actually just type the
64. 2:42number we actually need to put an
65. 2:44exclamation mark in front of that and
66. 2:46what that'll do is re-execute that
67. 2:49command in my case it's showing me the
68. 2:52command that you know that number refers
69. 2:55to and then I get the output of the
70. 2:57command which is basically just groups J
71. 2:59so essentially it's the same as I just
72. 3:01typed it in it's just giving me the
73. 3:02output but you know I can go ahead and
74. 3:05you know refer to it by number and
75. 3:07that's really important because you know
76. 3:09obviously none of these commands are
77. 3:11really hard
78. 3:11I can re-enter any of these commands
79. 3:14just as easily as I can scroll through
80. 3:16this list but again sometimes in Linux
81. 3:18you have really long commands and it's
82. 3:20just not practical to retype them and in
83. 3:22fact you open a margin of error for
84. 3:24possibly having a typo which is you know
85. 3:26potentially a really bad thing that you
86. 3:28could do so perhaps it's a good idea to
87. 3:31go ahead and look through here and you
88. 3:33can just execute the history or the
89. 3:35command accordingly now notice that
90. 3:37every time I enter a command so I just
91. 3:39do cat that's the passwd just a random
92. 3:43example and then I'll do history again
93. 3:48we can see that we have the command I
94. 3:52just entered automatically entered into
95. 3:54the history as I do LS and we see LS is
96. 3:59now in the history so every time we do
97. 4:02that we actually do see the command
98. 4:04being entered in which is great because
99. 4:05it keeps up and it enters all the
100. 4:07commands in there that we have run we'll
101. 4:11get back to the video in just a moment
102. 4:12but before we do I just wanted to
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125. 5:07back to the video what if we don't want
126. 5:11a command to be in the history so what
127. 5:15I'm going to do is type a space and then
128. 5:19I'm going to do sudo apt update to
129. 5:22update my package repositories I'll
130. 5:24press Enter and you know that that did
131. 5:30that so I'll clear the screen and let's
132. 5:32do history again wait a minute we don't
133. 5:36see the sudo apt update command here at
134. 5:39all I did just run it you saw me do it
135. 5:41but it's not listed and actually that's
136. 5:44a very common customization is that
137. 5:47anything with us or command with a space
138. 5:49in front of it is not actually going to
139. 5:51show up in the history now this is
140. 5:52dependent on the bash configuration and
141. 5:55each distribution ships a different
142. 5:58configuration for bash so yours might be
143. 6:00a little different than that but most
144. 6:02distributions will have a default
145. 6:04customization that omits command to
146. 6:07start with a space from the history why
147. 6:09would you want to hide a command from
148. 6:11your history well a couple examples
149. 6:13include maybe you have a command that
150. 6:16has sensitive information maybe it's a
151. 6:18old program where you have to type a
152. 6:20password and you know the bad thing is
153. 6:23if you're to do you know type a password
154. 6:26here I know this is not a good example
155. 6:27that's going to fail but it's in the
156. 6:29history right you know basically I just
157. 6:35pretend I typed a command that included
158. 6:36a password now it's in history so
159. 6:38somebody hacks into the server now they
160. 6:41could check the history file which is
161. 6:42you know pretty much usually viewable by
162. 6:44anyone and at that point they can get
163. 6:47the password so you don't want to
164. 6:50include a command
165. 6:52command that might include some
166. 6:54sensitive information you can type a
167. 6:56space in front of that so that way you
168. 6:58don't have to worry about a command that
169. 7:01has sensitive information being shown in
170. 7:03the history so a database server for
171. 7:05example if you need to type a database
172. 7:07password that's especially important you
173. 7:09don't want that in the history and one
174. 7:11way to avoid that if you can't omit the
175. 7:14password altogether is to put a space in
176. 7:16front so yeah I know that was a very
177. 7:18simple concept guys and I did want to
178. 7:21make sure that you guys understand
179. 7:23history and know how to get the history
180. 7:27and how to use it so yeah it's literally
181. 7:30that simple you have the history command
182. 7:31you can in most cases depending on the
183. 7:33configuration hide a command from
184. 7:35history if you put a space in front of
185. 7:36it you can use the number in front of an
186. 7:39item in the history to re execute that
187. 7:41command that's pretty powerful stuff and
188. 7:44another thing that also makes it very
189. 7:46powerful too is if you have a you know a
190. 7:48team of engineers and you know you want
191. 7:51to basically see what someone else did
192. 7:53to fix a problem history is
193. 7:55indispensable especially when you're
194. 7:56first starting a job at a new company
195. 7:58you're supporting a server you never
196. 8:00supported before you can use the history
197. 8:02command to find out how people have
198. 8:04solved similar problems in the past you
199. 8:07might actually find a command that was
200. 8:08used to resolve a problem because a lot
201. 8:10of cases problems do repeat and you can
202. 8:13find that information in the history it
203. 8:15can be valuable to go through the
204. 8:17history to see what others before you
205. 8:19have done to solve problems and if you
206. 8:22know there's a bad thing that happened
207. 8:23to the server you can also check the
208. 8:25history and it's a per-user thing but
209. 8:27you could check the history for the
210. 8:28users to find out it maybe if someone
211. 8:29made a mistake maybe they removed a file
212. 8:32that shouldn't have been removed or
213. 8:34something like that or if a server you
214. 8:36know went offline you might find that
215. 8:38they rebooted it or they shut it down
216. 8:39and then started to back up you'll see
217. 8:42those commands in the history so it's
218. 8:43just a good idea to know how to get to
219. 8:46those commands and the history is
220. 8:48indispensable so I highly recommend that
221. 8:50you guys familiarize yourself with the
222. 8:53history so there you go hope that was
223. 8:54helpful for you guys and I will see you
224. 8:57in the next video as soon as I have that
225. 8:59uploaded see you there thank you so much
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