三种shell脚本调用方法(fork, exec, source)

三种shell脚本调用方法(fork, exec, source)

原文: http://mindream.wang.blog.163.com/blog/static/2325122220084624318692/

fork(/path/to/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 /path/to/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:$$"
export A
echo "1.sh: $A is $A"
case in
    exec)
        echo "using exec…"
        exec ./2.sh ;;
    source)
        echo "using source…"
        . ./2.sh ;;
    *)
        echo "using fork by default…"
        ./2.sh ;;
esac
echo "PID for 1.sh after exec/source/fork:$$"
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