1+ ## LINUX COMMAND
2+
3+ ##DIRECTORY
4+
5+ sudo - super user do
6+ ---
7+ pwd --> displays present working directory
8+ ---
9+ mkdir (directory name) --> This command create a directory
10+ ---
11+ cd (directory/folder where you want to navigate) -->This command change directory.
12+ ---
13+ ls --> lists contents of current directory
14+ ---
15+ ls -l --> list contents of current directory with detailed output
16+ ---
17+ ll --> list contents of current directory with detailed output
18+ ---
19+ cd <folder>
20+ ---
21+ cd .. --> to come out of a directory
22+ ---
23+ rm -r testdir --> to remove a directory
24+ ---
25+ ~ --> Home directory
26+ ---
27+ mkdir -p folder/subfolder/subfolder2 --> create parent and child directory
28+
29+ ---
30+ ---
31+
32+ ##FILE
33+
34+ touch test.txt(file name) --> creates a empty file
35+ ---
36+ ls -l --> lists the contents in current directory
37+ ---
38+ echo Print Output
39+
40+ echo "This is a text" > test.txt
41+ ---
42+ cat test.txt --> writes the content of file into terminal & exits
43+ ---
44+ more test.txt --> writes the content of file on terminal page by page ( to move to next page need to hit space bar on keyboard )
45+ ---
46+ less test.txt --> open the file on terminal & can be read line by line (use arrows to scroll up & down)
47+
48+ To comeout need to press 'q' on the key board
49+ ---
50+ vi test.txt --> Visual Editor
51+ -This opens the file in read only mode
52+ -To edit the file, press 'i' on keyboard for INSERT mode & then you can write anything
53+ -once the text is entered, press 'ESC' on keyboard to return back on readonly mode
54+ -press ':wq' on keyboard -- to save & come out of the file
55+ -press ':q' on keyboard -- to come out of the file without saving
56+ -press ':wq!' on keyboard -- to save forcefully & come out of the file
57+ -press ':q!' on keyboard -- to come out of the file forcefully without saving
58+ ---
59+ rm test.txt --> To remove a file
60+ ---
61+ COPY/RENAME/MOVE/OPERATION
62+
63+ While performing these operations, we can always use absolute paths or relative paths accrodingly.
64+ These commands expects source & dest values
65+
66+ cp A.txt B.txt --> makes a copy of A.txt names it to B.txt in current directory
67+
68+ cp /home/A.txt /tmp/A.txt --> make a copy of A.txt to /tmp
69+
70+ cp -r testdir/ newdir/ --> makes a copy of testdir & names it to newdir in current dirctory
71+
72+ cp -r /home/testdir /tmp/testdir --> makes a copy of testdir to /tmp
73+
74+ mv A.txt new.txt ---> renames A.txt to new.txt in current path
75+
76+ mv A.txt /tmp ---> moves to A.txt to /tmp
77+
78+ mv testdir newdir --> renames testdir to newdir in crrent path
79+
80+ mv newdir /tmp ---> moves newdir to /tmp path
81+
82+ ---
83+
84+ ##PERMISSION
85+
86+ Observe the output of ls:
87+
88+ drwxrwxr-x 2 manifoldailearning manifoldailearning 4096 Nov 7 23:38 testdir
89+ -rw-rw-r-- 1 manifoldailearning manifoldailearning 126 Nov 7 23:37 abc.txt
90+ -rw-rw-r-- 1 manifoldailearning manifoldailearning 126 Nov 7 23:38 one.txt
91+
92+ drwxrwxr-x or -rw-rw-r-- --> Read/Write/Execute Permission for a file or a directory in linux
93+
94+ (1st value)manifoldailearning --> owner of the file/directory
95+ (2nd value)manifoldailearning --> group who owns file/directory
96+
97+ ---
98+
99+ How to update the owner & group for a file/dir -
100+
101+ chown ( change owner ) is the command to update the owners of dir/file
102+ note: note that you need to have previliges to update the permissions for a file/directory
103+
104+ Syntax: chown owner:group filename/dirname
105+
106+ ---
107+
108+ How to update the read,write & execute permissions for a file/dir
109+
110+ How to decode the Read/Write/Execute Permission terminology:
111+
112+ -/d ---> denotes if it is a file or directory ( - means file / d means directory )
113+ rwx ---> means read,write & execute permissions for super user ( root )
114+ rw- ---> means read,write permissions for the owner of the file ( ex: manifoldailearning as above )
115+ r-- ---> means read only permissions for others ( whoever login to the machine )
116+
117+
118+ r --> Permission to read the file.
119+ w --> Permission to write (or delete) the file.
120+ x --> Permission to execute the file, or, in the case of a directory, search it.
121+
122+ chmod ( change mode ) is the command to update the read/write/execute permissions for a file/directory
123+ r = 4, w = 2, x = 1
124+
125+ - | rwx | rwx | rwx
126+ - | 421 | 421 | 421
127+
128+ To update the permissions we can sum 421
129+ If super user needs to have read,write & exeute give 7
130+ If the owner need to read & write give 6
131+ If other need to have only read give 4
132+
133+
134+ chmod 777 file/dir -- rwx for root, rwx for owner, rwx for others
135+ chmod 764 file/dir -- rwx for root, rw for owner, r for others
136+ chmod 755 fire/dir -- rwx for root, rw for owner, rw for others
137+ v
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