随着shell脚本行数的增大，为了编写和维护的需要，想把一些特定的功能的代码抽取出来，组成函数的形式，放到一个叫做functions.sh中这样将来使用的时候只需要在脚本中source functions.sh 一下，然后就可以方便使用，处理大数据的时候，上篇博文提到过使用多线程处理是重要的手段，所以想到了写一个lock()函数，使得多个进程之间可以异步的工作。
函数的返回值有两种用途
1，返回函数结束的状态（可以是int，也可以是string）
2，共享一些变量
以下代码来自
(EDIT: This is also true for some other shells...)
1. echo strings
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lockdir="somedir"testlock(){ retval="" if mkdir "$lockdir" then # directory did not exist, but was created successfully echo >&2 "successfully acquired lock: $lockdir" retval="true" else echo >&2 "cannot acquire lock, giving up on $lockdir" retval="false" fi echo "$retval"}retval=$( testlock )if [ "$retval"=="true" ]then echo "directory not created"else echo "directory already created"fi |
2. return exit status
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lockdir="somedir"testlock(){ if mkdir "$lockdir" then # directory did not exist, but was created successfully echo >&2 "successfully acquired lock: $lockdir" retval=0 else echo >&2 "cannot acquire lock, giving up on $lockdir" retval=1 fi return "$retval"}testlockretval=$?if [ "$retval" == 0 ]then echo "directory not created"else echo "directory already created"fi |
3. share variable
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lockdir="somedir"retval=-1testlock(){ if mkdir "$lockdir" then # directory did not exist, but was created successfully echo >&2 "successfully acquired lock: $lockdir" retval=0 else echo >&2 "cannot acquire lock, giving up on $lockdir" retval=1 fi}testlockif [ "$retval" == 0 ]then echo "directory not created"else echo "directory already created"fi |
【NOTICE】关于shell函数的一个陷阱，我曾经深尝苦果，shell函数内部定义的变量，不是局部变量，这就意味着变量不会随着函数的结束而消失，这个特点可以被利用，所以shell函数中的变量要初始化，每次执行的时候注意重新赋值。