Shell script -for loop and for int loop

for loop

for((exp1; exp2; exp3))
do
    statements
done

Some notes ：

• exp1、exp2、exp3 Are three expressions , among exp2 It's the judgment condition ,for The loop is based on exp2 To decide whether to continue the next cycle ;
• statements It's a loop body statement , There can be one , There can be more than one ;
• do and done yes Shell Keywords in .

Code ： Calculate from 1 Add to 100 And .

#!/bin/bash
sum=0
for ((i=1; i<=100; i++))
do
    ((sum += i))
done
echo "The sum is: $sum"

Output ：

The sum is: 5050

for in loop

for variable in value_list
do
    statements
done

variable Said variable ,value_list Indicates the value list ,in yes Shell Keywords in .

Each cycle starts with value_list To assign a value to a variable variable, And then into the circulatory body （do and done Part between ）, Execute in loop body statements. Until the end of taking value_list All the values in , The cycle is over .

Code 1

#!/bin/bash
sum=0
for n in 1 2 3 4 5 6
do
    echo $n
     ((sum+=n))
done
echo "The sum is "$sum

Output ：

1
2
3
4
5
6
The sum is 21

Yes value_list Explanation

1) Give specific values directly

Can be in in The specific value is directly given after the keyword , Multiple values are separated by spaces , such as 1 2 3 4 5、“abc” “390” "tom" etc. .

Code :

#!/bin/bash
for str in "aaa" "bbb" "ccc" "ddd"
do
    echo $str
done

Output ：

aaa
bbb
ccc
ddd

2) Give a range of values

The specific format of a value range is ：

{start..end}

start Indicates the starting value ,end Indicates the end value ; Note that the middle is connected by two dots , Instead of three dots . According to the author's actual measurement , This form only supports numbers and letters .

Code 1: Calculate from 1 Add to 100 And

#!/bin/bash
sum=0
for n in {1..100}
do
    ((sum+=n))
done
echo $sum

Output ：

5050

Code 2: Output from A To z All characters between ：

#!/bin/bash
for c in {A..z}
do
    printf "%c" $c
done

Output ：

ABCDEFGHIJKLMNOPQRSTUVWXYZ[]^_`abcdefghijklmnopqrstuvwxyz

You can find ,Shell It's based on ASCII Code table to output .

3) Use the execution result of the command

Code 1： Calculate from 1 To 100 Between all even numbers and ：

#!/bin/bash
sum=0
for n in $(seq 2 2 100)
do
    ((sum+=n))
done
echo $sum

Output ：

2550

seq It's a Linux command , Used to generate integers in a certain range , And you can set the step size .
seq 2 2 100 From 2 Start , Each time 2, To 100 end .

Code 2： List all under the current directory Shell Script files ：

#!/bin/bash
for filename in $(ls *.sh)
do
    echo $filename
done

Output ：

demo.sh
test.sh
abc.sh

4) Use Shell wildcard

Shell Wildcards can be thought of as a kind of refined regular expression , Usually used to match directories or files , Not the text

Code ： Display all script files in the current directory

#!/bin/bash
for filename in *.sh
do
    echo $filename
done

Output ：

demo.sh
test.sh
abc.sh