Shell-related knowledge (1)

The Shell's own abilities.
Writing scripts is OK, at least now I'm running a script on the Internet
Program-Log scheduled backup and delete, NFS Shanghai volume file Delete and send mail.

"Data"
Export Path=/mall/jdk/jdk1.7/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin
Export LANG=ZH_CN. GB18030

start= ' Date +%s-d ' 2011-11-28 15:55:37 "'
end= ' Date +%s-d ' 2011-11-28 15:55:52 "'
echo $ (($end-$start))
Date "+%y-%m-%d%h:%m:%s"
Date-d ' +1 day ' + '%d ' Today +1
Date-s 20100405
Date-s 14:31:00

1. Late last month
Date-d ' Date +%y%m01 ' "-1 day" +%d
2. Forward
Date-d-' Date +%d ' Day +%d
3. Conditions
If [' Date +%d-d tomorrow ' = = 01];
4. Last month
Date-d Last-month
Date-d -1month
Date-d '-1 month ' + "%m"
5, next month
Date-d Next-month
Date-d 1month
6. Early this month
Date-d 1 ' Date +%b '
Early last month
Date-d 1 ' date-d last-month +%b '
Specify month
Day-d 1May

echo ' Date +%d ' | xargs-i{} date-d '-{} day ' +%y%m%d How Linux gets last month's end date

Sed-i "3s/.*/$table/g" conf/run.sql
Table=t_sms_mt_log_ ' date + "%m" ' this month, then the beginning of the month 1th is still counted last month
Date-d '-1 day ' + '%m ' this month, real this month
Subject= "Daily verification code issued quantity statistics _ ' date-d '-1 day ' +"%m%d ""

SELECT * from T_sys_user where user_code= ' duanzz ';

Update t_sys_user set terminal_id= ' 13730000000 ' where user_code= ' duanzz ';

Set Fileformat=unix

Intercept-Replace of string
Echo ${stringa:1} from the second place has been all
Echo ${stringa:2:5} intercepts 5 bits from the third position.

echo ${stringz: (-4)} Intercept from right to left
echo ${stringz:-4} Intercept from right to left, same as above
A=${STRINGA%%F} Remove the variable Stringa suffix F.
echo ${stringz/abc/xyz} variable in string ABC replaced by XYZ
echo ${stringz/#abc/xyz} with ' XYZ ' to replace the beginning ' abc '.
Echo ${STRINGZ/%ABC/XYZ} Replaces the end of ' abc ' with ' XYZ '.

You_id=${user}-on-${hostname}
you_id= $USER \-on-$HOSTNAME
echo $you _id root-on-db1 effect. Mixed output of variable and string
val=${1##+ (0)} # uses local variables to match the longest consecutive one or more 0.

Reference: ${backup_dir}/$DATE
#备份的变量:
Backup_dir=/home/mysql/mysql_bak
Date= ' date-d "+%y%m%d%h:%m:%d" '
Yes_time= ' date-d Yesterday "+%y%m%d" '
Mkdir-p/opt/chen$date\nailong Chen20160608nailong
Date-d "2 day Ago" + "%y-%m-%d" Yesterday date
date-d "1 week Ago" + "%y-%m-%d" last Sunday
Date +%y%m%d%h%m

The single quotation mark (') operation is basically the same as double quotes, but it is not allowed to reference a variable because the special meaning of $ is closed. In single quotation marks,
Any special characters are interpreted literally, except '. So the single quotation mark ("full reference") is a more than double quotation mark ("partial citation").
") more restrictive reference methods.

' Single quote mask all special characters
"" Double quotation marks mask some special characters

"Eval"

Two scans

Test.txt content: Hello Shell world!

Myfile= "Cat Test.txt"

(1) Echo $myfile #result: Cat test.txt

(2) eval echo $myfile #result: Hello Shell world!

"Echo"
ECHO-E handles special characters and interprets special characters. Effective special characters
Echo-n Non-newline output
Echo-e "A\NDDDD"//Automatic line wrapping
echo $ (ls-al) do not wrap echo "$ (ls-al)" Line wrap

bash$ Echo hello\!
Hello!
bash$ echo "hello\!"
hello\!
bash$ echo-e X\ty
Xty
bash$ echo-e "X\ty"
X y

echo "Chen" >> file: Append Chen content to file, without overwriting
echo "Chen" > file: Covered!!!

[A-za-z0-9]
Intercept Hello string: # var= ' Hello world! ' # echo ${var:0:5} Hello
Intercept World string: # Echo ${var:5:-1} World
Intercept the last character: # echo ${var: (-1)}!

########################  (( ... )) Structures can be used to calculate and test the results of an arithmetic expression.
#!/bin/bash
((5 > 4))
echo $?
echo "Exit Status of \" ((5 > 4)) \ "is $?."

"Input from keyboard-more than read"
Command << Word
Any input
Word

Read-p "Your command:" CMD
until [$CMD = = ' Q ']; Do
! Which $CMD && echo "wrong command" && read-p "Input again:" CMD && continue
Command= ' which $CMD | Grep-v "^alias" | Grep-o "[^[:space:]]\{1,\}" '
BINCP $COMMAND
echo "Copy $COMMAND finished."
Read-p "Continue:" CMD
Done

"Output to Screen"
Cat << Word
-----------
Name ID
Word
"Call in script" source _function.sh
"Shell function"
Hello ()
{
Echo ' Date '
}
Hello # # #这儿直接写hello
' Anti-quote allows you to assign the output of a shell command to a variable
today= ' Date +%y%m%d '
echo "Today is ' date +%y%m%d '"

Sleep 5 #过五秒再执行

"BaseName"
$ basename/tmp/test/file.txt
File.txt
$ basename/tmp/test/file.txt. txt
File

"DirName"
Dirname/var/log/messages get the path to a file or folder (previous level)
/var/log

Array
Var= ("123" "456" "789")
Var[1]=123
var[2]=456
echo "$var [1], $var [2]"
#

echo $? Condition is true, output 0, condition no, Output 1
CP 1.txt/opt/apps/2.txt >/dev/null 2>&1
Status=$?
echo $? #如果cp这个命令成功的话, output 0, unsuccessful, output 1

: The colon is here a placeholder, {str:=expr} if the variable str is not empty, ${str:=expr} equals the value of STR, and if Str is empty, the value of expr is assigned to STR
: >> target_file If this file does not exist before, create it
if [$name = ""] If this variable is a null value
Then: # doing nothing, branching out.
If [!-S 22.txt] If 22.txt this file is empty
or if [-Z 22.txt]

[$I-eq 1] && min= $MYRAND

If [-s $name] If this variable is empty
If [-D $path] If the directory exists
If [-s $path] if the directory exists
If [-N ""] # Tests whether there are command-line arguments (NOT null).
-A file exists YES!
-F This is a generic file
-D This is a directory
-B This is a fast device (floppy disk, hard drive, optical drive, etc.)
-C This is a character device (keyboard, sound card, etc.)
-P This file is a conduit
-H OR-l this is a symbolic link
-R file is readable
-W file is writable
-X file is executable
-O Whether you are a file owner
-G file Group-id is the same as you
F1-nt F2 file f1 than file F2 new
F1-ot F2 file F1 f2 older than file

Shell-related knowledge (1)