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Basic_Command
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## LINUX COMMAND
##DIRECTORY
sudo - super user do
---
pwd --> displays present working directory
---
mkdir (directory name) --> This command create a directory
---
cd (directory/folder where you want to navigate) -->This command change directory.
---
ls --> lists contents of current directory
---
ls -l --> list contents of current directory with detailed output
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ll --> list contents of current directory with detailed output
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cd <folder>
---
cd .. --> to come out of a directory
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rm -r testdir --> to remove a directory
---
~ --> Home directory
---
mkdir -p folder/subfolder/subfolder2 --> create parent and child directory
---
---
##FILE
touch test.txt(file name) --> creates a empty file
---
ls -l --> lists the contents in current directory
---
echo Print Output
echo "This is a text" > test.txt
---
cat test.txt --> writes the content of file into terminal & exits
---
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 )
---
less test.txt --> open the file on terminal & can be read line by line (use arrows to scroll up & down)
To comeout need to press 'q' on the key board
---
vi test.txt --> Visual Editor
-This opens the file in read only mode
-To edit the file, press 'i' on keyboard for INSERT mode & then you can write anything
-once the text is entered, press 'ESC' on keyboard to return back on readonly mode
-press ':wq' on keyboard -- to save & come out of the file
-press ':q' on keyboard -- to come out of the file without saving
-press ':wq!' on keyboard -- to save forcefully & come out of the file
-press ':q!' on keyboard -- to come out of the file forcefully without saving
---
rm test.txt --> To remove a file
---
COPY/RENAME/MOVE/OPERATION
While performing these operations, we can always use absolute paths or relative paths accrodingly.
These commands expects source & dest values
cp A.txt B.txt --> makes a copy of A.txt names it to B.txt in current directory
cp /home/A.txt /tmp/A.txt --> make a copy of A.txt to /tmp
cp -r testdir/ newdir/ --> makes a copy of testdir & names it to newdir in current dirctory
cp -r /home/testdir /tmp/testdir --> makes a copy of testdir to /tmp
mv A.txt new.txt ---> renames A.txt to new.txt in current path
mv A.txt /tmp ---> moves to A.txt to /tmp
mv testdir newdir --> renames testdir to newdir in crrent path
mv newdir /tmp ---> moves newdir to /tmp path
---
##Linux pipes
cat test.txt | grep 'searchkey' ---> Only gives lines from that file thant contains the key in ''
cat test.txt | less ---> Prints out file content, but you have the possibility to scroll
Quit the reading with 'q'
cat test.txt | uniq ---> This will sort the given file and print the unique values only.
cat test.txt | head -4 ---> Only prints out the last 4 lines of the command before the pipe, you can specify any number you want
ls | wc -l ---> prints out the linenumber of the command before the pipe
---
##PERMISSION
Observe the output of ls:
drwxrwxr-x 2 manifoldailearning manifoldailearning 4096 Nov 7 23:38 testdir
-rw-rw-r-- 1 manifoldailearning manifoldailearning 126 Nov 7 23:37 abc.txt
-rw-rw-r-- 1 manifoldailearning manifoldailearning 126 Nov 7 23:38 one.txt
drwxrwxr-x or -rw-rw-r-- --> Read/Write/Execute Permission for a file or a directory in linux
(1st value)manifoldailearning --> owner of the file/directory
(2nd value)manifoldailearning --> group who owns file/directory
---
How to update the owner & group for a file/dir -
chown ( change owner ) is the command to update the owners of dir/file
note: note that you need to have previliges to update the permissions for a file/directory
Syntax: chown owner:group filename/dirname
---
How to update the read,write & execute permissions for a file/dir
How to decode the Read/Write/Execute Permission terminology:
-/d ---> denotes if it is a file or directory ( - means file / d means directory )
rwx ---> means read,write & execute permissions for super user ( root )
rw- ---> means read,write permissions for the owner of the file ( ex: manifoldailearning as above )
r-- ---> means read only permissions for others ( whoever login to the machine )
r --> Permission to read the file.
w --> Permission to write (or delete) the file.
x --> Permission to execute the file, or, in the case of a directory, search it.
chmod ( change mode ) is the command to update the read/write/execute permissions for a file/directory
r = 4, w = 2, x = 1
- | rwx | rwx | rwx
- | 421 | 421 | 421
To update the permissions we can sum 421
If super user needs to have read,write & exeute give 7
If the owner need to read & write give 6
If other need to have only read give 4
chmod 777 file/dir -- rwx for root, rwx for owner, rwx for others
chmod 764 file/dir -- rwx for root, rw for owner, r for others
chmod 755 fire/dir -- rwx for root, rw for owner, rw for others
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