Linux01-bash script programming for signal capture and mission planning 53

First, the script programming knowledge point

1. Get the length of the character in the variable: ${#VARNAME}

2. Assigning values to variables:

A) ${parameter:-word}: If the parameter is empty or undefined, the variable is expanded to "word"; otherwise, the value is expanded to parameter;

such as: a=3

Echo ${a:-30}

Unset A

Echo ${a:-30}

b) ${parameter:+word}: If the parameter is empty or undefined, do nothing; otherwise, expand to "word" value;

such as: Echo ${a:+30}

A=1

Echo ${a:+30}

c) ${parameter:=word}: If parameter is empty or undefined, the variable is expanded to "word" and the expanded value is assigned to parameter;

such as: unset A

echo {a:=30}

D) ${parameter:offset}:offest means skipping a few;

e) ${parameter:offset:length}: Intercept substring, starting from the next character at offset and taking lenth long substring;

such as: A= ' Hello world '

echo {A:2:3}

3. Script configuration file

/etc/rc.d/init.d/service script, Service Script Support profile:/etc/sysconfig/Service script configuration file with the same name

4, variable scope, locals: local var_name=

such as: Edit a script, note where the function definition plus local and no local difference

#!/bin/bash

#

A=1

Test () {

Local A=$[3+4]

}

Test

For I in ' seq $a 10 '; Do

Echo $I

Done

5. Command mktemp: create temporary files or directories to avoid duplication with other filenames

Mktemp/tmp/file. XX (TMP directory is cleared by default for 30 days)

-D: Create as Directory

Second, signal capture

1. Signal:

Kill-signal PID

1:hup

2:int

9:kill

15:term

2, the script can achieve the signal capture, but 9 and 15 can not capture

Ctrl+c:sigint

3. Signal Capture command: Trap

Trap ' COMMAND ' signal list

such as: Edit a script to capture CTRL + C signal;

#!/bin/bash

#

Trap ' echo ' You go ... "' Int

While:;d o

Date

Sleep 2

Done

4, a row to execute multiple statements, the statement separated by semicolons;

Script instance:

Create a script ping.sh to capture the CTRL + C signal. and clean up the temporary files that are generated during the script run.

#!/bin/bash

#

network=192.8.8.

File= ' Mktemp/tmp/file. XX '

Clearup () {

echo "Quit ..."

RM-RF $FILE

Exit 1

}

Trap ' Clearup ' INT

For I in ' seq ten ';d o

If ping-c 1-w 1 $NETWORK $i &>/dev/null;then

echo "$NETWORK $i is up." | Tee >> $FILE

Else

echo "$NETWORK $i is down."

Fi

Done

III. Mission Plan

1. Task Plan mode:

A) perform a task at a future point in time;

At

Batch

b) To perform a task periodically;

Cron

2. At related

A) Use the format:

At time

At> COMMAND

At> Ctrl+d

b) Specify the time format:

Absolute time: hh:mm, DD. Mm. YY Mm/dd/yy

Relative Time: now+#

Units: minutes, hours, days, weeks

Blur Time: Noon, midnight, teatime

c) Options:

At-l = ATQ: Show jobs

at-d at_job_id = ATRM at_job_id: Deleting a job

d)/etc/at.deny and/etc/at.allow files

Control who uses the AT command

e) Execution result of the command: it will be sent to the user who scheduled the task in the form of mail;

3. Cron Related:

Cron: itself is an uninterrupted service that runs on the online host.

Anacron:cron, can be implemented to enable cron for various reasons in the past time the execution of the task is not performed, the resumption of normal execution once;

A) Cron:

A1) System cron Task: defined in/etc/crontab

Format: minutes, hours, days, months, weeks, user tasks

A2) User cron Task: defined in/var/spool/cron/username

Format: Minutes Hours day Month Week task

b) Valid value of time:

B1) minutes: 0-59

B2) Hours: 0-23

B3) Days: 1-31

B4) Month: 1-12

b5) Week: 0-7,0 and 7 both represent Sunday

c) Time-pass indication:

C1) *: All valid values corresponding to:

For example: The third minute of every hour: 3 * * * *

Third minute of every hour of the week: 3 * * 7

Daily 12:13:13 12 * * *

6th per month 12:13:13 12 6 * *

every year, July 6, 12:13:13 12 6 7 *

C2),: Discrete time point value:

For example: 10 minutes and 40 minutes per hour: 10,40 * * * *

every Tuesday Friday, 10 minutes and 40 minutes: 10,40 * * * 2,5

every Tuesday Friday 2 points 10 minutes 40 points: 10,40 02 * * 2,5

C3)-: Continuous point in time:

For example: Every Monday to Friday 2:10:10 02 * 1-5

c4)/#: How often in the corresponding value range,

Example: Every 3 minutes: */3 * * * *

every 2 hours: 01 */2 * * *

Every 1 hours: * */2 * * *

every other day: 10 04 */2 * *

d) Execution results will be emailed to the administrator;

such as: Only the wrong execution results are sent to the administrator:

*/3 * * * */bin/cat/etc/fstab >/dev/null

e) Cron environment variables: All cron execution commands go down the path specified by the PATH environment variable and add it in the script:

#!/bin/bash

Export Path=/bin:/sbin:/usr/bin:/usr/sbin

f) User Task Management command: crontab

-L: Lists all cron tasks for the current user

-E: Edit cron Task

-r: Remove all cron tasks

-u USERNAME: Managing cron tasks for other users

g) Cron Service

Service Crond Status

Chkconfig--list Crond

4, Anacron related

A)/etc/anacrontab file field (minimum time unit is daily)

First paragraph: not implemented in the past few days

The second paragraph: the number of minutes after the boot starts running

The third paragraph: represents the comment information

Fourth: Indicates the task performed

b) The Anacron service is turned off by default:

Service Anacron status

Cron Task Exercise:

Configure the machine to back up the/etc directory at 3:20 A.M. every two days, and the backup file to the/BACKUP/ETC directory. file name type: etc-2012-06-20.tar.bz2

*/2 * * root/bin/tar-jcf/backup/etc/etc-' date +%f '. tar.bz2/etc/*

This article is from "Nick Liu's blog," Please make sure to keep this source http://zkhylt.blog.51cto.com/3638719/1426060