- 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
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 $
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