Linux CLI Most Used Commands (ongoing)

whoami
#return current login user

man : display Manual of commands

man whoami
# to check mannual of a command
# use key 'Q' to escape 
# use 'SPACE' or 'ARROW' key to navigate
man man

ls : listing folder structures

cd: navigate folder structures

pwd
#current working directory
ls
ls -l #list with detailed info, e.g permission
ls -la #list hidden, .**
ls -a # .*

#go 1 level up, 2 level up
cd ..
cd ../../

Head,tail : peek content of a file (default 10 lines)

cat: concate files, display content of a file (full)

Sort: sort output lines (numerica or alphabic)

less: display file content with pagination

| : piping standard input to the next command

head file.txt #output first 10 lines (default)
head file.txt -n 100   #output first 100 lines
tail file.txt #output last 10 lines (default)
tail file.txt -n 100   #output the last 100 lines.
tail log.txt -f # nice to have to read logfile where it keeps update
cat file.txt #prints out all content

less file.txt #prints out all content with pagination
#within less
/patten #to search matching patten

# sort output 
# sort output of ls , -ru : reverse and unique values only and pipe it to wc to count lines
ls | sort -ru | wc -l
# sort output of ls, -n: sort on numbers 
ls | sort -n | wc -l

# display only unique lines from a file 
cat file.txt | sort -u
sort -u file.txt
# or combine it with uniq
# -d show only duplicated lines
sort file.txt | uniq -d
# -u only non duplicated lines
sort file.txt | uniq -u
# -c gives a count of each unique entries
sort file.txt | uniq -c
# to make it more fun, we can pipe it and sort it to give it a rank
sort file.txt | uniq -c | sort -n # low to high
sort file.txt | uniq -c | sort -nr # hight to low

>>, >: Edit file Content, redirect output into file. > repace >> concate

echo: print lines to console

# redirect output into a file with append mode
ls -la >> test.txt  
# redirect output into a file with replace mode
ls -la > test.txt  
# echo string to file
echo "test string " > test.txt
echo "test string " >> test.txt

wc: word counts

diff: compare file content differences

# count file # lines # of words # of bits
wc file.txt
man wc # to read more 

# use pipe to combine commands
# count lines of the output of ls -la
ls -la | wc

# concate file1.txt and file2.txt pipe it to wc and count lines/ words and bits
cat file1.txt file2.txt | wc

# the results of wc can also be redirected into a file like this
cat file1.txt file2.txt | wc > wcresult.txt

# compare two files , use man diff to read more 
diff filea.txt fileb.txt

rm, cp and mv: Copy , move and remove files / folder

cp -r  #recursive , to cp folder and its nested childs 
rm -r  #recursive , to rm folder and its nested childs

Expansions

# expansions

# print out all files names with .txt as extenion
echo *.txt
# print out all files start with a, b or cand with .txt as extension
echo {a,b,c}.txt 
# print out all files with two letter as extension
echo *.??
# print out 1 to 100
echo {1..100}
echo day{1..365}

# print out all app files where its extension in js, php or py
echo app.{js,php,py} 

Find

is used to search files with name/type/extension

Grep

is used to search content within a file.READMORE

#find files, find file with name in current directory
# find all files + directories with .py as extension
find . -name '*.py'
# find all directory with name start with cap A
find . -type d -name 'A*'
# -iname , case insensitive
find . -type d -iname 'A*'
# or operator 
# -type f , files only
find . -type d -iname 'A*' -or -name 'B*'

#grep keyword "green" from file.txt
grep green file.txt
#find keyword "green" case sensitive within all files and subfiles in /root/files 
grep -r "green" /root/files
#find keyword "green" case insensitive within all files and subfiles in /root/files
grep -ir "green" /root/files
# or if directory is not mentioned, it earches current active directory
grep -ir "green"
# grep also allows regular express -o prints only matching part of the lines
grep -rE -o '^[a-zA-Z0-9]*@[a-zA-Z].[com|nl]' file.txt

DU: display directory and files sizes

# -h human readable, -m megabytes, -g gigabyte
du -h /foldername
du -m /foldername 
du -g /foldername
#get all file size in human readable format and sort it from ASC humanreadable
du -h /foldername | sort -h 

du -h /foldername | sort -h | tail -12 # get the largest 12 files
du -h /foldername | sort -h | head -12 # get the smallest 12 files

DF: get disk usage information

df -h
df -h /folder

History: dispay history commands with sequence number

history | sort -r -n # display history and sort it large to small on number
  126  df
  125  history | sort -r -n
  124  history | sort -n
  123  history | sort -r -n
  122  history
  121  df -h
  120  clear
  119  du -h
  118  df
  117  clear
  116  du -h | sort -h | head 
  115  du -h | sort -h | tail -r -12
  114  du -h | sort -h | tail -12 -r
  113  du -h | sort -h | tail -12
  112  du -h | sort -h
  111  du -mh | sort -h
# here with "!" and the sequence number, can trigger run of the same command. it's called expansion
!121
# previous 10 history 
history -10

#pipe history to grep and file 'grre' in the output
history | grep  'grre'

PS: display running processes

ps             #display user processes
ps axww        #display all (user + system processes)

# display all processes and find Safari.app
ps axww | grep  'Safari.app'

Top: used to show all running processes lively dashboard

top           #sorting on CPU usage

top -o mem    #sorting on memory usage 

Kill:kill process

Killall: name

killall Safari
kill 3289283

# jobs, bg, and fg

jobs # display a list of running /pending/paused jobs
# bg or '&' sign run process in the background
fg # brings process to the foreground

gzip : create zip files from file to reduce size

gzip -k file.txt 
# this will create a new file called file.txt.gz
# use ls -lh to check file size
ls -lh

# -kv keep and vbose mode to show details of the zip 
gzip -kv file.txt 

# gzip -d = gunzip

Tar : used to create archives, used to group files into 1 single file

tar -cf groupfile.tar file1.txt file2.txt file3.txt
# - c f , create file name : groupfile.tar, group file 1, 2, 3

tar -tf groupfile.tar 
# - t f, shows what are files are in the .tar archives


tar -xf groupfile.tar
# extract all files within the archives in the current directory

tar -xf groupfile.tar -C /root/foldername
# to extract to specific folder 

# Combine tar archive with gzip!
# a new file is created and compressed
tar -czf groupfile.tar.gz file1.txt file2.txt file3.txt


# combine unzip and untar
tar -xf groupfile.tar.gz 

Nano: text editor in console

nano file.txt
# ctrl + k 
# to cut current line
# ctrl + u 
# to past cutted line

# ctrl + shift + 6 start select 
# use arrow key to select more 
# option + 6 to copy
# ctrl + u to paste

# navigation
# ctrl + A to the begining of current line
# ctrl + E to the end of current line
# ctrl + Y go to top
# ctrl + V go to end

there seems to be no redo and undo on Mac

# option + u  redo 
# option + e  undo

Alias: to create alias for commands

alias my_ls_lah='ls -lah'  # this way is not persistent

# add this line to .bashrc to make it persistent
# aad this line to .zshrc to make it persistent on Mac 

# Attention, "" and '' double and single quotes
alias a001="echo $PATH"
alias a002='echo $PATH'

# a001 the path varible to be fixed, even after new path is added after. you will not seee it
# a002 the path is expanded at run time, any new path is displayed.

xargs: similar to piping, but this is special arguments

find . -size +1M | xargs ls -lah

# find a files where size is larger than 1 mb and pipe arguments to ls -lah to display details 

ln : links, hard and soft links. they are like shortcuts on windows

# create a new hard link

ln file.txt filelink.txt

echo "new content" >> file.txt 
echo "new content" >> filelink.txt  
# does the same thing..

# even
rm file.txt 
# filelink.txt still there with content.

# create a soft link (windows shortcuts)
ln -s file.txt filelink.txt

# examples of link

ls -la /usr/bin/python*

lrwxr-xr-x  1 root  wheel      75 Feb  6 22:22 /usr/bin/python -> ../../System/Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7
lrwxr-xr-x  1 root  wheel      82 Feb  6 22:22 /usr/bin/python-config -> ../../System/Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7-config
lrwxr-xr-x  1 root  wheel      75 Feb  6 22:22 /usr/bin/python2 -> ../../System/Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7
lrwxr-xr-x  1 root  wheel      75 Feb  6 22:22 /usr/bin/python2.7 -> ../../System/Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7
lrwxr-xr-x  1 root  wheel      82 Feb  6 22:22 /usr/bin/python2.7-config -> ../../System/Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7-config
-rwxr-xr-x  1 root  wheel  167072 Feb  6 22:22 /usr/bin/python3
lrwxr-xr-x  1 root  wheel      76 Feb  6 22:22 /usr/bin/pythonw -> ../../System/Library/Frameworks/Python.framework/Versions/2.7/bin/pythonw2.7
lrwxr-xr-x  1 root  wheel      76 Feb  6 22:22 /usr/bin/pythonw2.7 -> ../../System/Library/Frameworks/Python.framework/Versions/2.7/bin/pythonw2.7

# where python command is pointing at 2.7

who : used to display users logged in to the system

Su : switch user

Sudo : super user do

Chown: change ownership

# list all groups 
groups 

# change group ownership

sudo chown work:root /folder

# change ownership of a file
sudo chown <USER> <FILE>

# change ownership of a folder
sudo chown -R <USER> <Folder>

#under stand permissions 

drwxr-xr-x

1	2	3	4	5	6	7	8	9	10
d	r	w	x	r	–	x	r	–	x
file type	read	write	execute	read	write	execute	read	write	execute

Position 1: indicates file type.

Position 2 ~ 4 : indicates Owner Rights

Position 5 ~ 7 : indicates Owner Group Rights

Position 8 ~ 10: indicates Everyone’s Rights

“x” on folders gives <cd> into permission. Without it, users cannot cd into the folder

---

chmod : used to change file/folder permissions

When specifying permissions with chmod, we use a special syntax to write permission statements.

First, we specify the “who” part using following values:

• u – user (the owner of the file/ folder)
• g – group (owner group)
• o – Others (the rest of the world)
• a – all of the above (u, g, o)

Next, we tell chmod “what” we are doing using the following characters:

• – (minus sign) removes a permission
• + (plus sign) to grant a permission
• = (equals sign) set a permission and removes others

Finally, the “which” values:

• r – the read permission
• w – the write permission
• x – the execute permission

# add write permission to group 

sudo chmod g+w file.txt

# remove write permission to All ( user, group and world)
sudo chmod a-w file.txt

# add multiple permission at the same time

sudo chmod g+rwx file.txt
sudo chmod o-rwx file.txt

# use "="

chmod g=r file.txt # will remove "wx" for group if exists (replace)
chmod g=rx file.txt # will remove "w" for group if exists (replace)

# change permission for user group at the same time

chmod ug+r file.txt # this will add read permission for user and group at the same time

Commands Chaining

; semi column || double pipe( or ) && ampersand ampersand ( and )

mkdir test || echo "directory already exisits"

Environment Variables

printenv

# to read all environment variables
printenv

echo $PATH 
# or 
printenv PATH