Shell basic applications and examples

Shell basic applications and examples

One

$# the number of arguments to the script

$* displays all parameters passed to the script in a single string. Unlike positional variables, this option parameter can be more than 9

$$ the current process ID number for the script to run

$! Process ID number of the last process running in the background

[Email protected] is the same as $*, but quotes are used, and each parameter is returned in quotation marks

$? Displays the exit status of the last command. 0 means there is no error, and any other value indicates an error.

$ A script name

$1..$9 Nth Parameter

Second, the function basic use:

function functname{

Shell commands

}

Or

Functname () {

Shell commands

}

Third, Bash's arithmetic operation comparison operator \ string comparison operator \ File comparison operator:

Tea tasting: This one is relatively full. Check the general, please click here.

1. Arithmetic Operation comparison operator (bash itself cannot compare floating-point numbers)

-eq equals [$num 1-eq $num 2]

-ne not equal to [100-ne $num 1]

-lt less than [100-lt ' expr $num 1 + $num 2 ']

-le less than or equal to [100-le ' expr $num 1 \* $num 2 ']

-GT greater than [100-gt ' expr $num 1/$num 2 ']

-ge greater than or equal to [100-ge ' expr $num 1 $num 2 ']

2. String comparison operators

-Z String True if string length is zero [-Z ' PS aux | grep MySQL ' "]

-N String if string length is nonzero, true [-n ' $string ']

"Note" $string must be placed in double quotation marks inside "$string", otherwise the result of using-n-z is true!

String1! = string2 true if string1 is different from string2 ["$str 1"! = "Snail"]

string1 = = string2 If string1 is the same as string2, then True ["$str 1" = = "$str 2"]

(above with one = can also be used under strict POSIX compatibility)

String1 string2 if string1 is more than string2 in dictionary order, true

Iv. File comparison Operators

-a filename if filename exists, true [-e $HOME/.BASHRC]

-e filename (ibid.)

-d filename If filename exists and is a directory, true [-d/home/snail]

-f filename If filename exists and is a regular file, true [-F/DEV/TTYS0]

-r filename If filename exists and is readable, true [-r/etc/passwd]

-u filename if filename exists and is Set-user-id, true [-f $HOME/ak47]

-W filename if filename exists and is writable, true [-w/var/log/mail]

-x filename If filename exists and is executable, true [-X./start.sh]

Five, a few common grammar

While basic usage:

while [condition]

Do

Command1

Command2

Command3

Done

#!/bin/bash

sudo find-type f-name ' *.log ' |while read mvname

Do

MV $mvname ${mvname/.log/. LOG}

Done

#!/bin/bash

#查找当前目录下 *.log and assign the value to Mvname to participate in the loop.

sudo find-type f-name ' *.log ' |while read mvname

Do

#移动, and replace the ending. Log with a. Log/*ubuntu.

MV $mvname ${mvname/.log/. LOG}

Done

Example: Above is a case of a batch replace file name bash

Simple PD file type, which can be written according to the above File Class form table:

#!/bin/bash

If [$#-ne 0]; Then

If [-D $]; Then

Echo is a Mulu

Else

echo $ D1 D2

Fi

If [-D + $]; Then

echo $ is a Mulu

Else

echo $ D1 D2

Fi

Fi

#!/bin/bash

#如果个数不为空的话

If [$#-ne 0]; Then

#如果 The first parameter is a table of contents

If [-D $]; Then

Echo is a Mulu

Else

echo $ D1 D2

Fi

If [-D + $]; Then

echo $ is a Mulu

Else

echo $ D1 D2

Fi

Fi

The program is just an example, there are many bugs in the middle, for example, if there are three parameters?

To make into a function to express:

#!/bin/bash

Set-x

ISD1 () {

echo $ D1 D2

}

If [$#-eq 2]; Then

If [-D $]; Then

Echo is a Mulu

Fi

If [-D + $]; Then

echo $ is a Mulu

Fi

Else

Isd1

Fi

Calculate the value change:

[Email protected]:/bash$ cat nubmer.sh

#!/bin/bash

A=1

b=2

Echo $a + $b

echo $ (($a + $b))

[Email protected]:/bash$ sudo sh nubmer.sh

1+2

3

This article is from the "Ten Years Sword-Breeze" blog, please be sure to keep this source http://jingfeng.blog.51cto.com/9152964/1880760

Shell basic applications and examples