Here’s a terminal command:
awk '/^Mem/ {print $4}' <(free -m)
Here’s my code:
class CSystemInfo{ public: std::string free_ram(){ std::string s; FILE *in; char buff[512]; //here is a prepared string (but with an error) if(!(in = popen("awk '/^Mem/ {print $4 "\t"}' <(free -m)","r"))){ return ""; } while(fgets(buff, sizeof(buff), in)!=NULL){ cout << s; s=s+buff; } pclose(in); return s; } }; CSystemInfo info; std::string ram = info.free_ram(); cout << ram;
The above code, when run, returns this message:
sh: 1: Syntax error: "(" unexpected
How can I place the ‘/’ symbol, for this command to work correctly?
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Answer
Your problem is not in C++. You are invoking your command with popen
, and popen
runs your command in sh
shell, that does not support <()
syntax, while in your terminal you are having bash
, zsh
or any other shell, that does support <()
syntax.
Edit: Better choise! Use pipes!
popen("free -m | awk ...")
Original answer, not working!: Try invoking bash
in popen
:
bash -c "awk '/^Mem/ {print $4}' <(free -m)"
in code:
popen("bash -c "awk '/^Mem/ {print $4}' <(free -m)"")