#!第一种写法 类似C、Java
for ((i=1; i<=100; i ++))
do
  echo $i  
done
#!第二种写法 in应用
for i in {1..100} 
do 
  echo $i 
done 
#!第三种写法 seq 使用
for i in `seq 1 100` 
do 
  echo $i 
done 

#!main.sh主体
#!/bin/sh
a=main

echo "a is $a"
echo "PID for parent before 2.sh:$$"
case $1 in
 exec)
  echo "using exec"
  exec ./2.sh ;;
 *)
  echo "using sourcing"
  source ./2.sh ;;
esac

echo "PID FOR parent after 2.sh :$$"

echo "now m"

#！2.sh
#!/bin/sh
echo "PID FOR 2.SH:$$"

echo "2.sh get a from main.sh is $a"

a=2.sh
export a
b=3.sh

echo "now 2.sh a is $a"

a is main
PID for parent before 2.sh:1162
using sourcing
PID FOR 2.SH:1162
2.sh get a from main.sh is main`这里写代码片`
now 2.sh a is 2.sh
PID FOR parent after 2.sh :1162
now m

#！main主函数
#!/bin/sh
a=0
for ((i=1; i<=10; i ++))
do
    a=$i
    echo "a is $a"
    echo "PID for parent before 2.sh:$$" 
        echo "using sourcing"
        source ./2.sh
     echo "PID FOR parent after 2.sh :$$"
    echo "now a is $a" 
done

a is 1
PID for parent before 2.sh:1339
using sourcing
PID FOR 2.SH:1339
2.sh get a from main.sh is 1
now 2.sh a is 2.sh
PID FOR parent after 2.sh :1339
now a is 2.sh
a is 2
PID for parent before 2.sh:1339
using sourcing
PID FOR 2.SH:1339
2.sh get a from main.sh is 2
now 2.sh a is 2.sh
PID FOR parent after 2.sh :1339
now a is 2.sh
a is 3
PID for parent before 2.sh:1339
using sourcing
PID FOR 2.SH:1339
2.sh get a from main.sh is 3
now 2.sh a is 2.sh
PID FOR parent after 2.sh :1339
now a is 2.sh
a is 4
PID for parent before 2.sh:1339
using sourcing
PID FOR 2.SH:1339
2.sh get a from main.sh is 4
now 2.sh a is 2.sh
PID FOR parent after 2.sh :1339
now a is 2.sh
a is 5
PID for parent before 2.sh:1339
using sourcing
PID FOR 2.SH:1339
2.sh get a from main.sh is 5
now 2.sh a is 2.sh
PID FOR parent after 2.sh :1339
now a is 2.sh
a is 6
PID for parent before 2.sh:1339
using sourcing
PID FOR 2.SH:1339
2.sh get a from main.sh is 6
now 2.sh a is 2.sh
PID FOR parent after 2.sh :1339
now a is 2.sh
a is 7
PID for parent before 2.sh:1339
using sourcing
PID FOR 2.SH:1339
2.sh get a from main.sh is 7
now 2.sh a is 2.sh
PID FOR parent after 2.sh :1339
now a is 2.sh
a is 8
PID for parent before 2.sh:1339
using sourcing
PID FOR 2.SH:1339
2.sh get a from main.sh is 8
now 2.sh a is 2.sh
PID FOR parent after 2.sh :1339
now a is 2.sh
a is 9
PID for parent before 2.sh:1339
using sourcing
PID FOR 2.SH:1339
2.sh get a from main.sh is 9
now 2.sh a is 2.sh
PID FOR parent after 2.sh :1339
now a is 2.sh
a is 10
PID for parent before 2.sh:1339
using sourcing
PID FOR 2.SH:1339
2.sh get a from main.sh is 10
now 2.sh a is 2.sh
PID FOR parent after 2.sh :1339
now a is 2.sh