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:
#!/bin/sh
a=main
echo "a is $a"
echo "PID for parent before 2.sh:$$"
case $1 in
exec)
echo "using exec"
exec ./2.sh ;;
source)
echo "using sourcing"
source ./2.sh ;;
*)
echo "using fork"
./2.sh ;;
esac
echo "PID FOR parent after 2.sh :$$"
echo "now main.sh a is $a"
echo "$b"
调用脚本: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"
执行结果:
[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]#
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