刚学的SHELL， shell怎么调用另一个shell的三种方式

转自：神勇小白鼠的博客
http://my.oschina.net/shootercn/blog/29186

 

看完小白鼠的这篇文章，原来不只是简简单单的调用，弄清区别也很重要。对于我目前的工作用exec方式调用估计用不到吧.

fork  ( /directory/script.sh)

fork是最普通的, 就是直接在脚本里面用/directory/script.sh来调用script.sh这个脚本.

运行的时候开一个sub-shell执行调用的脚本，sub-shell执行的时候, parent-shell还在。

sub-shell执行完毕后返回parent-shell. sub-shell从parent-shell继承环境变量.但是sub-shell中的环境变量不会带回parent-shell

exec (exec /directory/script.sh)

exec与fork不同，不需要新开一个sub-shell来执行被调用的脚本.  被调用的脚本与父脚本在同一个shell内执行。但是使用exec调用一个新脚本以后, 父脚本中exec行之后的内容就不会再执行了。这是exec和source的区别

source (source /directory/script.sh)

与fork的区别是不新开一个sub-shell来执行被调用的脚本，而是在同一个shell中执行. 所以被调用的脚本中声明的变量和环境变量, 都可以在主脚本中得到和使用.

 

 

可以通过下面这两个脚本来体会三种调用方式的不同:

1.sh 

#!/bin/bash

A=B 

echo "PID for 1.sh before exec/source/fork:$$"

export A

echo "1.sh: \$A is $A"

case $1 in

        exec)

                echo "using exec…"

                exec ./2.sh ;;

        source)

                echo "using source…"

                . ./2.sh ;;

        *)

                echo "using fork by default…"

                ./2.sh ;;

esac

echo "PID for 1.sh after exec/source/fork:$$"

echo "1.sh: \$A is $A"

2.sh 

#!/bin/bash

echo "PID for 2.sh: $$"

echo "2.sh get \$A=$A from 1.sh"

A=C

export A

echo "2.sh: \$A is $A"

 

执行情况：

$ ./1.sh     

PID for 1.sh before exec/source/fork:5845364

1.sh: $A is B

using fork by default…

PID for 2.sh: 5242940

2.sh get $A=B from 1.sh

2.sh: $A is C

PID for 1.sh after exec/source/fork:5845364

1.sh: $A is B

$ ./1.sh exec

PID for 1.sh before exec/source/fork:5562668

1.sh: $A is B

using exec…

PID for 2.sh: 5562668

2.sh get $A=B from 1.sh

2.sh: $A is C

$ ./1.sh source 

PID for 1.sh before exec/source/fork:5156894

1.sh: $A is B

using source…

PID for 2.sh: 5156894

2.sh get $A=B from 1.sh

2.sh: $A is C

PID for 1.sh after exec/source/fork:5156894

1.sh: $A is C

$