Linux Bash


sudo ssh-keygen -t rsa -f /etc/ssh/ssh_host_rsa_key
sudo service ssh start
sudo apt-get install openssh-server
#ssh config

start server:

sudo service ssh restart/start

A bug:

sudo ssh-keygen -t rsa -f /etc/ssh/ssh_host_ed25519_key

File server

python -m http.server
#default port: 8000

python -m http.server 80
#in port 80

program status

echo $?



This is a basic note about Linux shell, I have wrote plenty of bash shell, which helps solve problem easily.

Include system information, SSH, read -p, shell array, sed, AWK

System Information

Sometimes, you may want to see the system kernel version, 2 ways are available :

lsb_release -a
cat /etc/issue

change password for a user:

sudo passwd root

echo current time as a file name:

echo test >> $(date -d "today" +"%Y%m%d_%H%M%S").txt 
# work log
git log -4 > log/$(date -d "today" +"%Y%m%d").txt

Add Choice for User

read -p is very useful for this, for example:

read -n1 -p "What is your system version? 
1: Ubuntu 16.04;
2: Ubuntu 17.10;
3: Ubuntu 18.04;
choose a number between 1, 2 and 3: " answer
case $answer in
1) ...;;
2) ...;;
3) ...;;

Tips :

  • -n1 : -n and 1 are used together, which means read commmand will quit when system accept a single character, no need for Enter.
  • -s : this options will avoid displaying user passwords on the screen.
  • -t 5: overtime option, this means that user must complete the input within 5 seconds.

Shell Array

#get the content of arrary, or [*]
echo ${arraryName[@]}
#get the size of array
echo ${#arrayName[*]}


current_plugins_version=$(dpkg -s picoscenes-plugins-demo-rxsbroadcaster-chronos | grep Version | sed 's/Version: //g')

This is a basic use of sed, sed 's/Version: //g' means that a select :

Version: 18.0406.2333

Output is:


That means replace "Version: " with empty.

To replace the string in the file, use -i:

sudo sed -i 's/GRUB_HIDDEN_TIMEOUT=0/#GRUB_HIDDEN_TIMEOUT=0/g'  /etc/default/

This is an example that we do the CSI experiment, update the ~/etc/default/grub make the new kernel version could be seen.


tr 可以理解为sed的简化版本

Usage: tr [OPTION]... SET1 SET2

  • -c, -C, --complement: use the complement of SET1(不常用)

  • -d, -delete: delete characters in SET1

  • -s: replace each sequence of a repeated character, 删除所有重复出现字符序列,只保留第一个

tr -s 'the' 'my'
tr -s ' ' '\n'

tr -d 'the'

tr [a-z] [A-Z]

tr -s [a-zA-Z]


AWK Tutorial

which awk
$ usr/bin/awk

display the complete content of the files using AWK:

awk '{print}' xx.txt

AWK script:

create a text file command.awk containing the AWK command:


the use it:

awk -f command.awk xx.txt


# -v option
awk -v name=Jerry 'BEGIN{printf "Name = %s\n", name}'

awk --help

print column:

awk '{print $3 "\t" $4}' marks.txt

# or in any order
awk '{print $4 "\t" $3}' marks.txt

there we print the third and the fourth fields.

awk '/a/ {print $4 "\t" $3}' marks.txt

the pattern, only print 4 lines:

awk '/a/{++cnt} END {print "Count = ", cnt}' marks.txt
# Count = 4(where the marks.txt has 5 lines)

$0 variable stores the entire line and in the absence of a body block, default action is taken, i.e., the print action.

Last Updated: 12/28/2018, 8:55:15 AM