The command line in Linux is so incredibly powerful with so many functions available to you via the OS and optional applications you can install. It is often the easiest solution in C++ programs to just use the command line to achieve something you need doing rather than finding a harder way to do it in code and the following examples let you do just that.<\/p>\n\n\n\n
#include <stdlib.h>\n\t\/\/Console command:\n\tsystem(\"cp file.x newfile.x\");\n\n\t\/\/Execute file:\n\texeclp(\"\/usr\/bin\/omxplayer\", \" \", \"\/home\/pi\/projects\/game\/audio\/alpha.wav\", NULL);\t\t\/\/Execute file: file, arguments (1 or more strings followed by NULL - omxplayer has [OPTIONS] [FILE] hence the blank string)<\/code><\/pre>\n\n\n\nSystem Function (Calling shell)<\/h4>\n\n\n\n#include <stdlib.h>\n\n\n\tsystem(\"cp file.x newfile.x\");<\/code><\/pre>\n\n\n\nCall On A Background Thread<\/h4>\n\n\n\n
Can you get away with just adding a ‘&’ to the end of the line to cause it to be done in the background? If not:<\/p>\n\n\n\n
#include <unistd.h>\n\tint pid;\n\tpid=fork();\n\tif(pid==0)\n\t{\n\t\t\/\/printf(\"I am the child\\n\");\n\t\texeclp(\"\/usr\/bin\/omxplayer\", \" \", \"\/home\/pi\/projects\/game\/audio\/alpha.wav\", NULL);\t\t\/\/Execute file: file, arguments (1 or more strings followed by NULL - omxplayer has [OPTIONS] [FILE] hence the blank string)\n\t\t_exit(0);\n\t}\n\telse\n\t{\n\t\t\/\/printf(\"I am the parent\\n\");\n\t\twait();\n\t} <\/code><\/pre>\n\n\n\nRunning as a different root user<\/h4>\n\n\n\n
If your application has been run as root user with sudo because you are using the IO pins you may want to make command lines calls as the standard pi user. You can change to a different user using su – USERNAME -c before the command and surrounding it with quotes.<\/p>\n\n\n\n
\tsystem(\"su - pi -c \\\"fetchmail > \/dev\/null\\\"\");<\/code><\/pre>\n\n\n\nGetting The Result Of An Executed Console Command<\/h4>\n\n\n\n#include <string>\n#include <iostream>\n#include <stdio.h>\nusing namespace std; \/\/Or use std::string;\n\n\/\/************************************************************\n\/\/************************************************************\n\/\/********** EXECUTE CONSOLE COMMAND AND GET RESULT **********\n\/\/************************************************************\n\/\/************************************************************\n\/\/Note, this will return the output stdout. Some commands may generate a stderr response instead of stdout which you'd see on the console but this won't\n\/\/return, unless you simply add \" 2>&1\" to the end of your command string. Then you'll get the output of stdout and stderr\nstring do_console_command_get_result (char* command)\n{\n\tFILE* pipe = popen(command, \"r\");\t\t\/\/Send the command, popen exits immediately\n\tif (!pipe)\n\t\treturn \"ERROR\";\n\t\n\tchar buffer[128];\n\tstring result = \"\";\n\twhile(!feof(pipe))\t\t\t\t\t\t\/\/Wait for the output resulting from the command\n\t{\n\t\tif(fgets(buffer, 128, pipe) != NULL)\n\t\t\tresult += buffer;\n\t}\n\tpclose(pipe);\n\treturn(result);\n}<\/code><\/pre>\n\n\n\nIf you want to run a command \/ tool that will run continuously<\/h5>\n\n\n\n