Linux_Course

This blog records my Linux learning process.

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Commands

ls

ls [-a -l -h] [path]

“-a” shows some hidden directories or files.

“-l” shows more information.

“-h” shows the filesize which should be used with “-h”.

cd pwd

cd ./[path]  #workdir
cd ..        #predir
cd ~         #homedir

“cd” change directory
“pwd” print work directory

mkdir

mkdir [-p] path

Make directory
“-p” can create directory-chain

touch

touch filename   #create file
cat path         #show file
more path        #show file with pages

cp mv rm

copy move remove

cp [-r] copied copy   #"-r" copy dir
mv moved path/
rm [-r -f] para1 para2 ... paraN #"-r" remove dir "-f" force

““ refers to wildcard
e.g.:”test“ can represent test1 test2 test3

which find

which command
find startpath -name "filename"
find startpath -size +|-n[kMG] #"-10k" <10kb "+100M" >100Mb

grep wc Pipeline|

global regular expression print, Word count

grep [-n] "keyword" path  #"-n" show line number
wc [-c -m -l -w]          #"-c"bytesum "-m"charactersum
                          #"-l"linesum "-w"wordsum
cat filename | grep "keyword"

“left | right” left output is the input of right.

echo `` > >> tail

echo "output word"
echo `command`          #same as command > filename      #cover the file with the output
command >> filename     #add the output to the file
echo 'hello world' >> test.txt
tail [-f -num] path     #show tail line of the file
                        #"-f" can follow change immediately

root

su

switch user

su [-] [username] #"-" load environment var
exit              #back to the pre user

sudo

switch user do
the user who verified can sudo

sudo command
visudo          #verify user

usergroup

groupadd groupname
groupdel groupname

useradd [-g -d] username #"-g" add to existed group "-d" user home path
userdel [-r] username    #"-r" delete user homedir
id [username]            #check the usergroup
usermod -aG usergroup username #modify usergroup
getent [passwd group]                  #check all the usergroup

ls -l description

e.g.

1	2	3	4	5	6	7	8	9	10
d	rwx	rwx	r-x	4	xx	xx	4096	Feb 2 19:07	Desktop

Field 1- for File, d for Directory, l for Link

Field 2,3,4 Those are permissions that means read, write and execute, and comes in three different fields that belongs to the permission the:

• second: The owner has over the file
• third: The group has over the file
• fourth: Everybody else has over the file

Field 5 This field specifies the number of links or directories inside this directory.

Field 6 The user that owns the file, or directory.

Field 7 The group that file belongs to, and any user in that group will have the permissions given in the third field over that file.

Field 8 The size in bytes, you may modify this by using the -h option together with -l this will have the output in k,M,G for a better understanding.