Linux Shell Basic Learning--cycle and condition judgment

For loop

1. Note Do must wrap

For i in {1..10} do echo $idone

2. Note Do must wrap

For I in 1 2 3 4 5 do echo $idone

3. Traverse the results of the command output

For shname in ' ls *.sh ' do echo $shnamedone

4. For loops similar to high-level languages

For ((i=1;i<100;i++)) do echo $idone

The For loop is here, and these are enough.

While loop

Min=1max=100while [$min-le $max]do echo $min min= ' expr $min + 1 ' done

[] In the conditional expression,-le is less than equals, more can refer to the comparison operator

Until cycle

Min=0max=100until [$min-ge $max]do min= ' expr $min + 1 ' echo $mindone

If judgment, note the space

1. If

value=1if [$value-eq 1]; Then echo "true" fi

2. If...else

value=80if [$value-lt];then echo "fail" else echo "Success" fi

3. If...elif...else

value=80if [$value-lt];then echo "fail" elif [$value-ge];then echo "good" else echo "Success" fi

4. && | | Operation

value=80if [$value-ge 0] && [$value-le];then echo "ok" fi

Arithmetic expressions (for add, subtract, multiply, divide, take-up)

Expr expression

i=1i= ' expr $i + 1 ' echo $ii =$ (expr $i-1) echo $i

Let expression

I=10let i= $i +1echo $ilet i*=2echo $i

Using declare

Declare-i numnum= $num +1echo $num

$ ((expression))

i=2i=$ ((i+1)) echo $i

Linux Shell Basic Learning--cycle and condition judgment