从Shell脚本返回值而不使用echo

Question

I have c++ code which includes a system call which in turn calls a bash oneliner

if (system("if [ `ls | wc -l` -eq 1 ]; then return 0 ; else return 1; fi") != 0)
    std::cout << "returned non zero" << std::endl;
else
    std::cout << "returned zero" << std::endl;

This doesn't work since I get this error

-bash: return: can only `return' from a function or sourced script

If I use echo instead of return I get the return code of the echo command instead the value passed to echo . Any idea how to go around this?

Answer 1

You don't really need return, just change your code to this:

if ( system( "[ `ls | wc -l` -eq 1 ]" ) != 0)
    std::cout << "returned non zero" << std::endl;
else
    std::cout << "returned zero" << std::endl;

This code:

[ `ls | wc -l` -eq 1 ]

will return 0 or 1 as per the condition and system will return that status to your C++ code.

Answer 2

You want to use exit 0 and exit 1 in your bash command. Note that 0 typically means success, while non-0 means there was some error.