exec 和 source的区别

source 就是让 script 在当前 shell 内执行、而不是产生一个 sub-shell 来执行。由
exec 也是让 script 在同一个行程上执行，但是原有行程则被结束了。

source ./my.script
 或： . ./my.script
 也就是简而言之：原有行程会否终止，就是 exec 与 source/fork 的最大差异了。

代码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 ./.sh ;;  #执行完成后结束
        source)
                echo "using source...."
                . ./.sh ;;  #执行完成后继续执行
        *)
                echo "using fork by default...."
                ./.sh ;;  #另起一个进程来执行 .sh 执行后继续执行1.sh
esac

echo "PID FOR 1.sh after exec/source/fork :$$"
echo "1.sh:\$A is $A"

代码 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"

修改文件权限：

 chmod  .sh
 chmod  .sh

测试代码：

$ ./.sh fork
$ ./.sh source
$ ./.sh exec

结果：

# ./.sh exec
PID FOR .sh before exec/source/fork:
.sh:$A is B
using exec,,,,,
PID for .sh:
.sh get $A=B from .sh
.sh: $A is C

# ./.sh source
PID FOR .sh before exec/source/fork:
.sh:$A is B
using source....
PID for .sh:
.sh get $A=B from .sh
.sh: $A is C
PID FOR .sh after exec/source/fork :
.sh:$A is C

# ./.sh fork
PID FOR .sh before exec/source/fork:
.sh:$A is B
using fork by default....
PID for .sh:
.sh get $A=B from .sh
.sh: $A is C
PID FOR .sh after exec/source/fork :
.sh:$A is B