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.

vim intro
vim versatile
vim cheatsheet
vim plugins

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 dd or yy right 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 one and replace the first one by two
:s/one/two/g ? ? ?at the current line, search one and replace all the one by two
:%s/one/two/g ?search the entire text file and replace one by two
?string ? ? ? ? ? ? ?serach specified pattern from bottom to top
/string ? ? ? ? ? ? ? ?search specified pattern from top to bottom

Tricks

select all（high light）：press esc，then ggvG or ggVG
copy all：press esc，then ggyG
delete all：press esc，then ggdG

gg：move cursor to the first line，it only works on vim
v ： enter the visual mode
G ：move cursor to the last line
select the data content，then：
d delete the selected portion
y copy the selected portion to 0registor
+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/

What is a Shell?

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
$[\, conditional-statement\, ]$ $\Leftarrow$ Notice the right space
$\Uparrow$
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
[ $USER != root ] || echo "root"
[root@linuxprobe chap4_vim_shell]# ./shell-express.sh 
1
0
exist
root
root
```
Tips:
&& / logical and : if and only if the prior expression is true
|| / logical or : if and the prior expression is false then the post expression will start
! / logical NOT : take the negation of the expression, e.g. true => false
```
(base) /loveplay1983@($)-> [ $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 $?
1

free 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
fi

read -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'
esac

read -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 at command
- Periodically do the same tasks, e.g. Backup your /home directory at each Monday Morning $\Rightarrow$ home.backup.tar.xz
With at command
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.

at command uses interactive mode to configure the schedule

[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

at command with pipe

[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

list and delete specific schedule

[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 linuxprobe

Do the task after a particular timeline

linuxprobe@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 crontab command

[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.

image.png

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/

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2021-01-14 VIM and Shell

2021-01-14 VIM and Shell

VIM

Tricks

Practise

Shell Script

Practise

Scheduled Task

相關(guān)閱讀更多精彩內(nèi)容

友情鏈接更多精彩內(nèi)容

色偷偷精品伊人,欧洲久久精品,欧美综合婷婷骚逼,国产AV主播,国产最新探花在线,九色在线视频一区,伊人大交九 欧美,1769亚洲,黄色成人av

2021-01-14 VIM and Shell

VIM

Tricks

Practise

Shell Script

Practise

Scheduled Task

相關(guān)閱讀更多精彩內(nèi)容

友情鏈接更多精彩內(nèi)容

色偷偷精品伊人,欧洲久久精品,欧美综合婷婷骚逼,国产AV主播,国产最新探花在线,九色在线视频一区,伊人大交九欧美,1769亚洲,黄色成人av