Basic use of Shell statements

1 if statement

echo "Please input X"

Read X

echo "Please input Y"

Read Y

If [$x-gt $y]; In the [] condition, there must be a space before the [only space is followed]. Only a semicolon can be available, or there can be no semicolon

Then

echo "$x Dayu $y"

elif [$x-lt $y];

Then

echo "$x Xiayu $y"

Else

echo "$x Dengyu $y"

Fi

2. addition (multiplication)

sum= ' expr $x + $y ' integer calculation, to add expr, and to have spaces on both sides of the +

echo "The result is $sum"

If it's a multiplication. ' Expr $x * $y ' need ' for translation

3. Save the return code of the previous command

["$x" = "$y"]

echo $?? can be used to save the return code of the previous command. Correct return of 0, wrong return 1

4.for statement

Total=0

The For ((i=1;i<=100;i++)) is followed by a double bracket (()). The inside of a general (()) is used for some computational

Todo

Total= ' expr $total + $i '

Done

echo "The result is $total"

5.while statement

1) total=0; Num=0 on the same line, but separated by semicolons

2) Total=0 Num=0 agreed to the line, but no separator these three kinds of effects are the same

3) total=0

Num=0 is written in two lines.

while (NUM<100) a while is also a double bracket (())

Todo

num= ' expr $num + 1 '

Total= ' expr $total + $num '

Done

In 6.until, the condition is True end loop

Until [$num-ge] until is [] to judge, here can not use <, if-gt

Todo

num= ' expr $num + 1 '

Total= ' expr $total + $num '

Done

7. For loop there is a conditional judgment of if

For ((i=1;i<=10;i++)) This, for the inside easy to forget to write do and done

Todo

if ((i%2==1))

Then

Rcho "Jishu is $i"

Else

echo "Oushu is $i"

Fi

Done

8. Case statement

Read X

A= $x

Case $a in

1)

echo "The NUM is 1";; At the end of each sentence there are two semicolons;; this is necessary.

2)

echo "The NUM is 2"; echo "Hehhehe";; Output two lines, and is a newline, between the two sentences with a semicolon link;

3|4)

echo "The NUM is 3 or 4";; A condition has multiple values, this time with a "|" to separate

*)

echo "The NUM is other";; For other possible conditions, use "*" to indicate

Esac

9 Functions and calling

Add () function body

{

sum= ' expr $x + $y '

echo "The sum is $ sum"

}

echo "Please input X"

Read X

echo "Please input Y"

Read Y

Add $x $y function call

10. Call to Script

In script 1, if you call script 2. Add a line "./script2" directly to script 1