Linux Learning Note 2015-12-09

The beginning of the script needs to use #!/bin/bash to start the script, in the script, it is best to use the # comment comments, develop good habits

In the system, the default is a variable reply variable

In declare you can define the type of a variable

Declare-i a------defines a as integral type

You can use echo $ to find the return value, the correct command return value is 0, the wrong return positive value

In Linux, you can use test to compare values.

The syntax is: Test $AA-lt $BB--------to determine that the AA variable is less than the BB variable

You can also use the [] bracket to compare

The syntax is: [$AA-gt $BB]-----Represents the contrast of the variable AA greater than the variable BB. If it is true

Returns 0, error returns non 0 positive

Judging 1 && Judging 2--------"and" connectors must be true on both sides before returning

If the judge 1 is false, then do not go to Judge 2, return False

Summary:&& must be true for 2 sides, then return True

Judgment 1 | | Judge 2--------"or" connector, as long as one side is true, the execution returns to True

If Judge 1 is false, proceed to judgment 2 and Judge 2 as true

will return to the true

Summary: | | One side is true, it returns true

Conditional Judgment Statement

Grammar:

if Judgment statement; Then

Command

Elif judgment statement; then

Command

Else

Command

Fi

eg

#!/bin/bash

grep ^$1/etc/passwd

If ["$?"-eq 0];then

echo "This account exists"

Else

echo "This account does not exist"

Fi

Example 2:

#!/bin/bash

echo "Please enter your Age:"

Read name

If [$name-lt 0] | | [$name-gt];then

echo "Please enter the correct age"

elif [$name-le];then

echo "Hello, young man"

elif [$name-le];then

echo "Hello, middle-aged"

Else

echo "Hello, Old man"

Fi

Define a functional function

Grammar

function Test () {

echo "This is a function"

}

Test #直接用函数名即可调用执行此函数

Cycle

While [judgment statement]------conditions until the end loop is not established

Do

Command

Done

Until [judgment statement]---------condition is not established until the condition is set to the end of the cycle

Do

Command

Done

For loop

For XX in value 1 value 2 value 3 .....

Do

Command

Done

Linux Learning Note 2015-12-09