VIM
Vim is a highly configurable text editor built to make creating and changing any kind of text very efficient. It is included as "vi" with most UNIX systems and with Apple OS X.
control mode: manipulate cursor movement, copy, paste, delete, search, etc...
input mode: basic text input
last line mode: configure the editor options, save, quit, etc...
vim basic editing
vim frequently used commands
- dd delete the line where the cursor is
- 2dd delete 2 lines starts from the current cursor
- yy copy the entire line of data from the current cursor
- 2yy copy 2 lines starts form the current cursor
- n locate the next string that matches the searching pattern
- N locate the previous string that matches the searching pattern
- u undo the previous manipulation
-
p paste the text data from the last
ddoryyright after the cursor
Last Line Mode commands
- :w save the file
- :q exit the current text file
- :q! forced to exit the current text file which will lose all the unsaved text content
- :wq! forced to save and exit the current text file
- :set nu show line numbers
- :set nonu disable line numbers
- :command execute the eligible commands(inside of vim editor)
- :integer jump to the specified line number
-
:s/one/two at the current line, search
oneand replace the firstonebytwo -
:s/one/two/g at the current line, search
oneand replace all theonebytwo -
:%s/one/two/g search the entire text file and replace
onebytwo - ?string serach specified pattern from bottom to top
- /string search specified pattern from top to bottom
Tricks
select all（high light）：press
esc，thenggvGorggVG
copy all：pressesc，thenggyG
delete all：pressesc，thenggdG
gg：move cursor to the first line，it only works on
vim
v ： enter thevisual mode
G ：move cursor to the last line
select the data content，then：
d delete the selected portion
y copy the selected portion to0registor
+y copy the selected portion to+registor, i.e. the system clipboard, then other programs can use it
Practise
- add new data without
:w
# The following line just be added without :w
select all（high light）：press esc，then ggvG or ggVG
copy all：press esc，then ggyG
delete all：press esc，then ggdG
E37: No write since last change (add ! to override)
- change hostname
vim /etc/hostname
(base) /loveplay1983@($)-> hostname
deepgiant
- configure network
Shell Script
https://linuxhint.com/30_bash_script_examples/
https://www.ubuntupit.com/simple-yet-effective-linux-shell-script-examples/
https://www.softwaretestinghelp.com/shell-scripting-interview-questions/
At its base, a shell is simply a macro processor that executes commands. The term macro processor means functionality where text and symbols are expanded to create larger expressions.
Unix shell is both a command interpreter and a programming language. As a command interpreter, the shell provides the user interface to the rich set of GNU utilities. The programming language features allow these utilities to be combined. Files containing commands can be created, and become commands themselves. These new commands have the same status as system commands in directories such as /bin, allowing users or groups to establish custom environments to automate their common tasks.
Practise
- Create a simple script
# .sh extension indicates this file is a shell script file
# #!/bin/bash tells the system to use the bash interpreter to execute the script
#!/bin/bash
pwd
ls -al
- run the shell script
(base) /loveplay1983@($)-> ./example.sh
bash: ./example.sh: Permission denied
(base) /loveplay1983@($)-> chmod u+x example.sh
(base) /loveplay1983@($)-> ./example.sh
-
Accept user input or args
image.png# .sh extension indicates this file is a shell script file # #!/bin/bash tells the system to use the bash interpreter to execute the script #!/bin/bash echo "script name => $0" echo "total number of args => $#" echo "the 1st parameter is $1, the 5th parameter is $5" (base) /loveplay1983@($)-> ./example.sh x1 x2 x3 x4 x5 script name => ./example.sh total number of args => 5 the 1st parameter is x1, the 5th parameter is x5 -
Conditional test
Shell script can use the conditional statement for testing the expression, 0 if the result is true, not non-zero otherwise
Notice the right space
Notice the left space- -d test whether the target is directory
- -e test whether the file exists
- -f test whether the file is an ordinary file
- -r test the read permission
- -w test the write permission
- -x test the execute permission
[root@linuxprobe chap4_vim_shell]# cat shell-express.sh #!/bin/bash # Warnining!, Notice the space in between the square braces [ -d /etc/fstab ] echo $? # print out the last result [ -f /etc/fstab ] echo $? # print out the last result # logic and [ -e /dev/cdrom ] && echo "exist" # logic or [ $USER = root ] || echo "user" # logic not [ $USER != root ] || echo "root" [root@linuxprobe chap4_vim_shell]# ./shell-express.sh 1 0 exist root rootTips:
&& / logical and : if and only if the prior expression is true
|| / logical or : if and the prior expression is false then the post expression will start
! / logical NOT : take the negation of the expression, e.g. true => false(base) /loveplay1983@($)-> [ $USER != root ] && echo "user" || echo "root" user -
Integer comparison
- -eq 是否等于
- -ne 是否不等于
- -gt 是否大于
- -lt 是否小于
- -le 是否等于或小于
- -ge 是否大于或等于
(base) /loveplay1983@($)-> echo $? 0 (base) /loveplay1983@($)-> [ 10 -ne 10 ] (base) /loveplay1983@($)-> echo $? 1free memory detection
#!/bin/bash # Detect the free memory freeMem=`free -m | grep Mem: | awk '{print $4}'` [ $freeMem -lt 1024 ] && echo "Insufficient Memory" root@deepgiant:/home/loveplay1983/linux/shell# ./checkMem.sh 10892
-
String comparison
- = check the equality of the strings
- != check whether the strings are different
- -z check whether the string is empty
#!/bin/bash #Check equality of strings [ -z $1 ] if [ $? -eq 0 ] then echo "The string is not empty." else echo "It is an empty string." fi #!/bin/bash if [ ! $LANG = "en_US.UTF-8" ] then echo " Not en.US" else echo "en.US" fi -
if...then...fi; if....then....else...fi; if...then...elif...then...else...fi
#!/bin/bash # if then fi if # test for condition then # action list fi # assert the if statement is finished # if then else fi if then else fi # if then elif then else fi if then elif then else firead -p "Enter your score(0-100): " GRADE if [ $GRADE -ge 90 ] && [ $GRADE -le 100 ] then echo "Your grade is excellent!" elif [ $GRADE -ge 70 ] && [ $GRADE -le 89 ] then echo "Your grade is not bad!" else echo "Your grade is a little bit sad!!!" fi -
for loop
# for loop will take many objects at one time and do the operations one by one for # take all the objects in # the object list do # actions one by one done- detect and add users
read -p "Enter the user password???" PASSWD for UNAME in `cat users.txt` do id $UNAME &> /dev/null if [ $? -eq 0 ] then echo "$UNAME, already exists" else useradd $UNAME &> /dev/null echo "$PASSWD" | passwd --stdin $UNAME &> /dev/null echo "$UNAME, Create success" fi done- ping a list of hosts
#!/bin/bash host_list=$(cat hosts.txt) for ip in $host_list do echo $ip ping -c 3 -i 0.2 -W $ip &> /dev/null if [ $? -eq 0 ] then echo "Host $ip is on-line." else echo "Host $ip is off-line." fi done -
while loop
while loop walks through a list of executions repeatedly until it meets the break, it often doesn't know the exact number of repetitions.while # condition do # actions done# expr - evaluate the expression PRICE=$(expr $RANDOM % 1000) # random number mod # will yield a random number in the range of 0-# TIMES=0 echo "price is in the range of 0-999, please guess it?!!" while true do read -p "Enter the price: " price let TIMES++ if [ $price -eq $PRICE ] then echo "Congrats, the actual price is $PRICE" echo "Total guessed number $TIMES" exit elif [ $price -gt $PRICE ] then echo "Too High" else echo "Too low" fi done -
case statement
case :'var-value' in :'pattern' :'commands' ;; :'pattern' :'commands' ;; :'...' *) :'default commands' esacread -p "enter a character, end up with enter key" KEY case "$KEY" in [a-z][A-Z]) echo "you have entered letters" ;; [0-9]) echo "you have entered digits" ;; *) echo "you have entered data other than letters and digits" esac
Scheduled Task
- There at 2 ways to do the automatic tasks
- Do something at a particular time with
atcommand - Periodically do the same tasks, e.g. Backup your /home directory at each
Monday Morninghome.backup.tar.xz
- Do something at a particular time with
- With
atcommand
https://linuxconfig.org/how-to-schedule-tasks-using-at-command-on-linux- -f file Reads the job from file rather than standard input
- -q Uses the specified queue.
- -l Display the pending job list
- -d Delete the particular pending job
- -m Send email to the user after the job is done
at and batch read commands from standard input or a specified file which are to be executed at a later time, using /bin/sh.
-
atcommand uses interactive mode to configure the schedule
at command with pipe[linuxprobe@linuxprobe ~]$ at 22:00 warning: commands will be executed using /bin/sh at> apat update at> apt autoremove at> apt autoclean at> <EOT> job 1 at Mon Jan 18 22:00:00 2021
list and delete specific schedule[linuxprobe@linuxprobe ~]$ echo "systemctl restart sshd" | at 22:30 warning: commands will be executed using /bin/sh job 2 at Mon Jan 18 22:30:00 2021
Do the task after a particular[linuxprobe@linuxprobe ~]$ at -l 1 Mon Jan 18 22:00:00 2021 a linuxprobe 2 Mon Jan 18 22:30:00 2021 a linuxprobe [linuxprobe@linuxprobe ~]$ atrm 2 [linuxprobe@linuxprobe ~]$ at -l 1 Mon Jan 18 22:00:00 2021 a linuxprobetimelinelinuxprobe@linuxprobe ~]$ at now +1 HOUR warning: commands will be executed using /bin/sh at> apt clean at> apt autoclean at> <EOT> job 3 at Mon Jan 18 22:33:00 2021 [linuxprobe@linuxprobe ~]$ - With
crontabcommand
[linuxprobe@linuxprobe home]$ systemctl status crond
● crond.service - Command Scheduler
Loaded: loaded (/usr/lib/systemd/system/crond.service; enabled; vendor preset: enabled)
Active: active (running) since Tue 2021-01-19 01:36:47 CST; 15s ago
Main PID: 11729 (crond)
Tasks: 1 (limit: 49666)
Memory: 1.1M
CGroup: /system.slice/crond.service
└─11729 /usr/sbin/crond -n
https://ostechnix.com/a-beginners-guide-to-cron-jobs/
https://www.tutorialspoint.com/unix_commands/crontab.htm
crontab is the program used to install, deinstall or list the tables used to drive the cron daemon in
Vixie Cron. Each user can have their own crontab, and though these are files in/var/spool/cron/crontabs, they are not intended to be edited directly.
One of the most useful utility that you can find in any Unix-like operating system. It is used to schedule commands at a specific time. These scheduled commands or tasks are known as "Cron Jobs". Cron is generally used for running scheduled backups, monitoring disk space, deleting files (for example log files) periodically which are no longer required, running system maintenance tasks and a lot more. In this brief guide, we will see the basic usage of Cron Jobs in Linux.
- To display the contents of the crontab file of the currently logged in user
crontab -l
- Edit the current user's cron jobs
crontab -e
# If the editor is selected wrongly, you may use `select-editor` to choose again
Select an editor. To change later, run 'select-editor'.
1. /bin/nano <---- easiest
2. /usr/bin/vim.basic
3. /usr/bin/vim.tiny
4. /bin/ed
Choose 1-4 [1]:
- To edit the crontab of a different user, for example loveplay1983
crontab -u loveplay1983 -e
- Examples
# To run a cron job at every minute
* * * * * <command-to-execute>
# To run cron job at every 5th minute
*/5 * * * * <command-to-execute>
# To run a cron job at every quarter hour (i.e every 15th minute)
*/15 * * * * <command-to-execute>
# To run a cron job every hour at minute 30
30 * * * * <command-to-execute>
# You can also define multiple time intervals separated by commas. For example, the following cron job will run three times every hour, at minute 0, 5 and 10
0,5,10 * * * * <command-to-execute>
# Run a cron job every half hour i.e at every 30th minute
*/30 * * * * <command-to-execute>
# Run a job every hour (at minute 0)
0 * * * * <command-to-execute>
# Run a job every 2 hours
0 */2 * * * <command-to-execute>
# Run a job every day (It will run at 00:00)
0 0 * * * <command-to-execute>
# Run a job every day at 3am
0 3 * * * <command-to-execute>
# Run a job every Sunday
0 0 * * SUN <command-to-execute> / 0 0 * * 0 <command-to-execute>
# Run a job on every day-of-week from Monday through Friday i.e every weekday
0 0 * * 1-5 <command-to-execute>
# Run a job every month (i.e at 00:00 on day-of-month 1)
0 0 1 * * <command-to-execute>
# Run a job at 16:15 on day-of-month 1
15 16 1 * * <command-to-execute>
# Run a job at every quarter i.e on day-of-month 1 in every 3rd month
0 0 1 */3 * <command-to-execute> # 每季度
# Run a job on a specific month at a specific time
5 0 * 4 * <command-to-execute>
# Run a job every 6 months
0 0 1 */6 * <command-to-execute>
# Run a job every year
* * 1 1 * <command-to-execute>
We can also use the following strings to define job
@reboot Run once, at startup.
@yearly Run once a year.
@annually (same as @yearly).
@monthly Run once a month.
@weekly Run once a week.
@daily Run once a day.
@midnight (same as @daily).
@hourly Run once an hour.
e.g.
@reboot <command-to-execute>
- To remove all cron jobs for the current user
crontab -r
- Crontab syntax generator
https://crontab.guru/
https://crontab-generator.org/
