linux中exec、source、fork区别
在运行shell脚本时候,有三种方式来调用外部的脚本,exec(exec script.sh)、source(source script.sh)、fork(./script.sh)
1、exec(exec /home/script.sh):
使用exec来调用脚本,被执行的脚本会继承当前shell的环境变量。但事实上exec产生了新的进程,他会把主shell的进程资源占用并替换脚本内容,继承了原主shell的PID号,即原主shell剩下的内容不会执行。
2、source(source /home/script.sh)
使用source或者“.”来调用外部脚本,不会产生新的进程,继承当前shell环境变量,而且被调用的脚本运行结束后,它拥有的环境变量和声明变量会被当前shell保留,类似将调用脚本的内容复制过来直接执行。执行完毕后原主shell继续运行。
3、fork(/home/script.sh)
直接运行脚本,会以当前shell为父进程,产生新的进程,并且继承主脚本的环境变量和声明变量。执行完毕后,主脚本不会保留其环境变量和声明变量。
总结:这样来看fork最灵活,source次之,exec最诡异。
主脚本:
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1 #!/bin/sh 2 a=main 3 4 echo "a is $a" 5 echo "PID for parent before 2.sh:$$" 6 case $1 in 7 exec ) 8 echo "using exec" 9 exec . /2 .sh ;; 10 source ) 11 echo "using sourcing" 12 source . /2 .sh ;; 13 *) 14 echo "using fork" 15 . /2 .sh ;; 16 17 esac 18 19 echo "PID FOR parent after 2.sh :$$" 20 21 echo "now main.sh a is $a" 22 echo "$b" |
调用脚本:2.sh
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1 #!/bin/sh 2 echo "PID FOR 2.SH:$$" 3 4 echo "2.sh get a from main.sh is $a" 5 6 a=2.sh 7 export a 8 b=3.sh 9 10 echo "now 2.sh a is $a" ~ ~ |
执行结果:
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[root@lvs2 home] # ./main.sh exec a is main PID for parent before 2.sh:19026 using exec PID FOR 2.SH:19026 2.sh get a from main.sh is main now a is 2.sh [root@lvs2 home] # ./main.sh source a is main PID for parent before 2.sh:19027 using sourcing PID FOR 2.SH:19027 2.sh get a from main.sh is main now a is 2.sh PID FOR parent after 2.sh :19027 now main.sh a is 2.sh 3.sh [root@lvs2 home] # ./main.sh fork a is main PID for parent before 2.sh:19028 using fork PID FOR 2.SH:19029 2.sh get a from main.sh is main now a is 2.sh PID FOR parent after 2.sh :19028 now main.sh a is main [root@lvs2 home] # |
本文出自 “DanielQu” 博客:http://qujunorz.blog.51cto.com/6378776/1541676