Some experience and skills accumulated in five years of using Linux

Some experience and skills accumulated in five years of using Linux_PHP tutorial

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Release： 2016-07-21 15:05:04

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1. $ related parameters in bash

Copy code The code is as follows:

$0 - represents the current File name 
$* - Separate all parameters with spaces to form a string 
$@ - Separate all parameters with spaces to form a string combination. The difference with $* is that when quoted by "", "$*" is a string, while "$@" contains multiple strings 
$# - the number of parameters passed to the process 
$? - The execution result of the previous command, if there is no error, is 0 
$$ - The PID of this command 

2. bash technique, combine the contents of a variable into another variable Variable name
EXAMPLE:

Copy code The code is as follows:

A_B_C_D ="something" 
t1="B" 
t2="_D" 
eval echo $A_${t1}_C${t2}; 

3 . Under Ubuntu (12.04, 12.10), ThinkPad 🎜>
echo -n 225 > /sys/devices/platform/i8042/serio1/serio2/sensitivity echo -n 115 > /sys/devices/platform/i8042/serio1/serio2/speed

4. Back up the master boot sector (bootsector)

If the boot file is damaged, you can restore it by restoring the master boot sector:

Backup

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The code is as follows:

dd if=/dev/hda of=bootsector.img bs=512 count = 1 >dd if=bootsector.img of=/dev/hda

The above two steps only restore the main boot sector. It is very likely that you need to restore all the contents of /boot to start normally, so You can also back up the files under /boot. 5. Bash command line input skills:

Use Ctrl+R to search for previously used commands

Use Ctrl+W to delete the current single item
Use Ctrl+U to delete Current line 

6. xargs is very powerful, you can use -l{} to specify the location of parameters:
EXAMPLE

Copy code The code is as follows:

cat hosts | >
set -e, when an error occurs, the script will exit 
set -u, when bash finds that there are no initialized variables, it will exit 

For more reference: "Writing Robust Bash Scripts" 》

8. tar packages the files listed in the specified list:

Copy the code
The code is as follows:

cat yourlist.lst

/etc/fstab /home/admin/bin/somefile.sh /home/mysql/somefile ... tar cvzf xxx. tar.gz -T yourlist.lst

9. Specify a DNS server to query domain name records

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The code is as follows:

dig @8.8.8.8 www.google.com

10. The parameters that need most attention in the sort command are -k and - s:

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 The code is as follows: 

-s, --stable 
 stabilize sort by disabling last-resort comparison

stable indicates that the final order depends on the original order.

EXAMPLE

Copy code The code is as follows:

$ cat a.txt 
 a 

A
b
$ sort -f a.txt a

A B $ sort -f -s a.txt a

b 

 In the example, -f means case-insensitive, -s means the order depends on the order of the original file

Copy code The code is as follows:

-k, --key=POS1[,POS2] 
 start a key at POS1 (origin 1), end it at POS2 (default end of line). 

So to sort only by the second column, you should write:

Copy the code The code is as follows:

sort -k1,1