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From here I have the code that gives me the command line output and the exit code. Unfortunately I don't understand much of that operator overloading and if I try to rewrite it to the simple code I know (with global variables i.e.) I always get the wrong exit code status of 0.
So how can I modify the following code so I can store the output and the exit code status for future use?
#include <cstdio>
#include <iostream>
#include <memory>
#include <stdexcept>
#include <string>
#include <array>
struct CommandResult {
std::string output;
int exitstatus;
friend std::ostream &operator<<(std::ostream &os, const CommandResult &result) {
os << "command exitstatus: " << result.exitstatus << " output: " << result.output;
return os;
}
bool operator==(const CommandResult &rhs) const {
return output == rhs.output &&
exitstatus == rhs.exitstatus;
}
bool operator!=(const CommandResult &rhs) const {
return !(rhs == *this);
}
};
class Command {
public:
/**
* Execute system command and get STDOUT result.
* Like system() but gives back exit status and stdout.
* #param command system command to execute
* #return CommandResult containing STDOUT (not stderr) output & exitstatus
* of command. Empty if command failed (or has no output). If you want stderr,
* use shell redirection (2&>1).
*/
static CommandResult exec(const std::string &command) {
int exitcode = 255;
std::array<char, 1048576> buffer {};
std::string result;
#ifdef _WIN32
#define popen _popen
#define pclose _pclose
#define WEXITSTATUS
#endif
FILE *pipe = popen(command.c_str(), "r");
if (pipe == nullptr) {
throw std::runtime_error("popen() failed!");
}
try {
std::size_t bytesread;
while ((bytesread = fread(buffer.data(), sizeof(buffer.at(0)), sizeof(buffer), pipe)) != 0) {
result += std::string(buffer.data(), bytesread);
}
} catch (...) {
pclose(pipe);
throw;
}
exitcode = WEXITSTATUS(pclose(pipe));
return CommandResult{result, exitcode};
}
};
int main ()
{
std::cout << Command::exec("echo blablub") << std::endl;
}
Here is my code, the global variable is correct in the function but is overwritten afterwards.
#include <cstdio>
#include <iostream>
#include <memory>
#include <stdexcept>
#include <string>
#include <array>
int exitcode = 555;
std::string exec(const std::string cmd) {
int exitcode = 255;
std::array<char, 128> buffer {};
std::string result;
#ifdef _WIN32
#define popen _popen
#define pclose _pclose
#define WEXITSTATUS
#endif
FILE *pipe = popen(cmd.c_str(), "r");
if (pipe == nullptr) {
throw std::runtime_error("popen() failed!");
}
try {
std::size_t bytesread;
while ((bytesread = fread(buffer.data(), sizeof(buffer.at(0)), sizeof(buffer), pipe)) != 0) {
result += std::string(buffer.data(), bytesread);
}
} catch (...) {
pclose(pipe);
throw;
}
exitcode = WEXITSTATUS(pclose(pipe));
std::cout<<exitcode<<'\n';
return result;
}
int main (){
exec("echo bla");
std::cout<<exitcode<<'\n';
}
Assuming the code provided in the article is correct and does what it should do, it is already doing all you need. The exit code and output are returned from the exec function.
You only have to use the returned CommandResult and access its members:
int main() {
auto result = Command::exec("echo blablub");
std::cout << result.output << "\n":
std::cout << result.exitstatus << "\n";
}
I am looking for a way to get the output of a command when it is run from within a C++ program. I have looked at using the system() function, but that will just execute a command. Here's an example of what I'm looking for:
std::string result = system("./some_command");
I need to run an arbitrary command and get its output. I've looked at boost.org, but I have not found anything that will give me what I need.
#include <cstdio>
#include <iostream>
#include <memory>
#include <stdexcept>
#include <string>
#include <array>
std::string exec(const char* cmd) {
std::array<char, 128> buffer;
std::string result;
std::unique_ptr<FILE, decltype(&pclose)> pipe(popen(cmd, "r"), pclose);
if (!pipe) {
throw std::runtime_error("popen() failed!");
}
while (fgets(buffer.data(), buffer.size(), pipe.get()) != nullptr) {
result += buffer.data();
}
return result;
}
Pre-C++11 version:
#include <iostream>
#include <stdexcept>
#include <stdio.h>
#include <string>
std::string exec(const char* cmd) {
char buffer[128];
std::string result = "";
FILE* pipe = popen(cmd, "r");
if (!pipe) throw std::runtime_error("popen() failed!");
try {
while (fgets(buffer, sizeof buffer, pipe) != NULL) {
result += buffer;
}
} catch (...) {
pclose(pipe);
throw;
}
pclose(pipe);
return result;
}
Replace popen and pclose with _popen and _pclose for Windows.
Getting both stdout and stderr (and also writing to stdin, not shown here) is easy peasy with my pstreams header, which defines iostream classes that work like popen:
#include <pstream.h>
#include <string>
#include <iostream>
int main()
{
// run a process and create a streambuf that reads its stdout and stderr
redi::ipstream proc("./some_command", redi::pstreams::pstdout | redi::pstreams::pstderr);
std::string line;
// read child's stdout
while (std::getline(proc.out(), line))
std::cout << "stdout: " << line << '\n';
// if reading stdout stopped at EOF then reset the state:
if (proc.eof() && proc.fail())
proc.clear();
// read child's stderr
while (std::getline(proc.err(), line))
std::cout << "stderr: " << line << '\n';
}
For Windows, popen also works, but it opens up a console window - which quickly flashes over your UI application. If you want to be a professional, it's better to disable this "flashing" (especially if the end-user can cancel it).
So here is my own version for Windows:
(This code is partially recombined from ideas written in The Code Project and MSDN samples.)
#include <windows.h>
#include <atlstr.h>
//
// Execute a command and get the results. (Only standard output)
//
CStringA ExecCmd(
const wchar_t* cmd // [in] command to execute
)
{
CStringA strResult;
HANDLE hPipeRead, hPipeWrite;
SECURITY_ATTRIBUTES saAttr = {sizeof(SECURITY_ATTRIBUTES)};
saAttr.bInheritHandle = TRUE; // Pipe handles are inherited by child process.
saAttr.lpSecurityDescriptor = NULL;
// Create a pipe to get results from child's stdout.
if (!CreatePipe(&hPipeRead, &hPipeWrite, &saAttr, 0))
return strResult;
STARTUPINFOW si = {sizeof(STARTUPINFOW)};
si.dwFlags = STARTF_USESHOWWINDOW | STARTF_USESTDHANDLES;
si.hStdOutput = hPipeWrite;
si.hStdError = hPipeWrite;
si.wShowWindow = SW_HIDE; // Prevents cmd window from flashing.
// Requires STARTF_USESHOWWINDOW in dwFlags.
PROCESS_INFORMATION pi = { 0 };
BOOL fSuccess = CreateProcessW(NULL, (LPWSTR)cmd, NULL, NULL, TRUE, CREATE_NEW_CONSOLE, NULL, NULL, &si, &pi);
if (! fSuccess)
{
CloseHandle(hPipeWrite);
CloseHandle(hPipeRead);
return strResult;
}
bool bProcessEnded = false;
for (; !bProcessEnded ;)
{
// Give some timeslice (50 ms), so we won't waste 100% CPU.
bProcessEnded = WaitForSingleObject( pi.hProcess, 50) == WAIT_OBJECT_0;
// Even if process exited - we continue reading, if
// there is some data available over pipe.
for (;;)
{
char buf[1024];
DWORD dwRead = 0;
DWORD dwAvail = 0;
if (!::PeekNamedPipe(hPipeRead, NULL, 0, NULL, &dwAvail, NULL))
break;
if (!dwAvail) // No data available, return
break;
if (!::ReadFile(hPipeRead, buf, min(sizeof(buf) - 1, dwAvail), &dwRead, NULL) || !dwRead)
// Error, the child process might ended
break;
buf[dwRead] = 0;
strResult += buf;
}
} //for
CloseHandle(hPipeWrite);
CloseHandle(hPipeRead);
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
return strResult;
} //ExecCmd
I'd use popen() (++waqas).
But sometimes you need reading and writing...
It seems like nobody does things the hard way any more.
(Assuming a Unix/Linux/Mac environment, or perhaps Windows with a POSIX compatibility layer...)
enum PIPE_FILE_DESCRIPTERS
{
READ_FD = 0,
WRITE_FD = 1
};
enum CONSTANTS
{
BUFFER_SIZE = 100
};
int
main()
{
int parentToChild[2];
int childToParent[2];
pid_t pid;
string dataReadFromChild;
char buffer[BUFFER_SIZE + 1];
ssize_t readResult;
int status;
ASSERT_IS(0, pipe(parentToChild));
ASSERT_IS(0, pipe(childToParent));
switch (pid = fork())
{
case -1:
FAIL("Fork failed");
exit(-1);
case 0: /* Child */
ASSERT_NOT(-1, dup2(parentToChild[READ_FD], STDIN_FILENO));
ASSERT_NOT(-1, dup2(childToParent[WRITE_FD], STDOUT_FILENO));
ASSERT_NOT(-1, dup2(childToParent[WRITE_FD], STDERR_FILENO));
ASSERT_IS(0, close(parentToChild [WRITE_FD]));
ASSERT_IS(0, close(childToParent [READ_FD]));
/* file, arg0, arg1, arg2 */
execlp("ls", "ls", "-al", "--color");
FAIL("This line should never be reached!!!");
exit(-1);
default: /* Parent */
cout << "Child " << pid << " process running..." << endl;
ASSERT_IS(0, close(parentToChild [READ_FD]));
ASSERT_IS(0, close(childToParent [WRITE_FD]));
while (true)
{
switch (readResult = read(childToParent[READ_FD],
buffer, BUFFER_SIZE))
{
case 0: /* End-of-File, or non-blocking read. */
cout << "End of file reached..." << endl
<< "Data received was ("
<< dataReadFromChild.size() << "): " << endl
<< dataReadFromChild << endl;
ASSERT_IS(pid, waitpid(pid, & status, 0));
cout << endl
<< "Child exit staus is: " << WEXITSTATUS(status) << endl
<< endl;
exit(0);
case -1:
if ((errno == EINTR) || (errno == EAGAIN))
{
errno = 0;
break;
}
else
{
FAIL("read() failed");
exit(-1);
}
default:
dataReadFromChild . append(buffer, readResult);
break;
}
} /* while (true) */
} /* switch (pid = fork())*/
}
You also might want to play around with select() and non-blocking reads.
fd_set readfds;
struct timeval timeout;
timeout.tv_sec = 0; /* Seconds */
timeout.tv_usec = 1000; /* Microseconds */
FD_ZERO(&readfds);
FD_SET(childToParent[READ_FD], &readfds);
switch (select (1 + childToParent[READ_FD], &readfds, (fd_set*)NULL, (fd_set*)NULL, & timeout))
{
case 0: /* Timeout expired */
break;
case -1:
if ((errno == EINTR) || (errno == EAGAIN))
{
errno = 0;
break;
}
else
{
FAIL("Select() Failed");
exit(-1);
}
case 1: /* We have input */
readResult = read(childToParent[READ_FD], buffer, BUFFER_SIZE);
// However you want to handle it...
break;
default:
FAIL("How did we see input on more than one file descriptor?");
exit(-1);
}
Two possible approaches:
I don't think popen() is part of the C++ standard (it's part of POSIX from memory), but it's available on every UNIX I've worked with (and you seem to be targeting UNIX since your command is ./some_command).
On the off-chance that there is no popen(), you can use system("./some_command >/tmp/some_command.out");, then use the normal I/O functions to process the output file.
The following might be a portable solution. It follows standards.
#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
#include <sstream>
std::string ssystem (const char *command) {
char tmpname [L_tmpnam];
std::tmpnam ( tmpname );
std::string scommand = command;
std::string cmd = scommand + " >> " + tmpname;
std::system(cmd.c_str());
std::ifstream file(tmpname, std::ios::in | std::ios::binary );
std::string result;
if (file) {
while (!file.eof()) result.push_back(file.get())
;
file.close();
}
remove(tmpname);
return result;
}
// For Cygwin
int main(int argc, char *argv[])
{
std::string bash = "FILETWO=/cygdrive/c/*\nfor f in $FILETWO\ndo\necho \"$f\"\ndone ";
std::string in;
std::string s = ssystem(bash.c_str());
std::istringstream iss(s);
std::string line;
while (std::getline(iss, line))
{
std::cout << "LINE-> " + line + " length: " << line.length() << std::endl;
}
std::cin >> in;
return 0;
}
I couldn't figure out why popen/pclose is missing from Code::Blocks/MinGW. So I worked around the problem by using CreateProcess() and CreatePipe() instead.
Here's the solution that worked for me:
//C++11
#include <cstdio>
#include <iostream>
#include <windows.h>
#include <cstdint>
#include <deque>
#include <string>
#include <thread>
using namespace std;
int SystemCapture(
string CmdLine, //Command Line
string CmdRunDir, //set to '.' for current directory
string& ListStdOut, //Return List of StdOut
string& ListStdErr, //Return List of StdErr
uint32_t& RetCode) //Return Exit Code
{
int Success;
SECURITY_ATTRIBUTES security_attributes;
HANDLE stdout_rd = INVALID_HANDLE_VALUE;
HANDLE stdout_wr = INVALID_HANDLE_VALUE;
HANDLE stderr_rd = INVALID_HANDLE_VALUE;
HANDLE stderr_wr = INVALID_HANDLE_VALUE;
PROCESS_INFORMATION process_info;
STARTUPINFO startup_info;
thread stdout_thread;
thread stderr_thread;
security_attributes.nLength = sizeof(SECURITY_ATTRIBUTES);
security_attributes.bInheritHandle = TRUE;
security_attributes.lpSecurityDescriptor = nullptr;
if (!CreatePipe(&stdout_rd, &stdout_wr, &security_attributes, 0) ||
!SetHandleInformation(stdout_rd, HANDLE_FLAG_INHERIT, 0)) {
return -1;
}
if (!CreatePipe(&stderr_rd, &stderr_wr, &security_attributes, 0) ||
!SetHandleInformation(stderr_rd, HANDLE_FLAG_INHERIT, 0)) {
if (stdout_rd != INVALID_HANDLE_VALUE) CloseHandle(stdout_rd);
if (stdout_wr != INVALID_HANDLE_VALUE) CloseHandle(stdout_wr);
return -2;
}
ZeroMemory(&process_info, sizeof(PROCESS_INFORMATION));
ZeroMemory(&startup_info, sizeof(STARTUPINFO));
startup_info.cb = sizeof(STARTUPINFO);
startup_info.hStdInput = 0;
startup_info.hStdOutput = stdout_wr;
startup_info.hStdError = stderr_wr;
if(stdout_rd || stderr_rd)
startup_info.dwFlags |= STARTF_USESTDHANDLES;
// Make a copy because CreateProcess needs to modify string buffer
char CmdLineStr[MAX_PATH];
strncpy(CmdLineStr, CmdLine.c_str(), MAX_PATH);
CmdLineStr[MAX_PATH-1] = 0;
Success = CreateProcess(
nullptr,
CmdLineStr,
nullptr,
nullptr,
TRUE,
0,
nullptr,
CmdRunDir.c_str(),
&startup_info,
&process_info
);
CloseHandle(stdout_wr);
CloseHandle(stderr_wr);
if(!Success) {
CloseHandle(process_info.hProcess);
CloseHandle(process_info.hThread);
CloseHandle(stdout_rd);
CloseHandle(stderr_rd);
return -4;
}
else {
CloseHandle(process_info.hThread);
}
if(stdout_rd) {
stdout_thread=thread([&]() {
DWORD n;
const size_t bufsize = 1000;
char buffer [bufsize];
for(;;) {
n = 0;
int Success = ReadFile(
stdout_rd,
buffer,
(DWORD)bufsize,
&n,
nullptr
);
printf("STDERR: Success:%d n:%d\n", Success, (int)n);
if(!Success || n == 0)
break;
string s(buffer, n);
printf("STDOUT:(%s)\n", s.c_str());
ListStdOut += s;
}
printf("STDOUT:BREAK!\n");
});
}
if(stderr_rd) {
stderr_thread=thread([&]() {
DWORD n;
const size_t bufsize = 1000;
char buffer [bufsize];
for(;;) {
n = 0;
int Success = ReadFile(
stderr_rd,
buffer,
(DWORD)bufsize,
&n,
nullptr
);
printf("STDERR: Success:%d n:%d\n", Success, (int)n);
if(!Success || n == 0)
break;
string s(buffer, n);
printf("STDERR:(%s)\n", s.c_str());
ListStdErr += s;
}
printf("STDERR:BREAK!\n");
});
}
WaitForSingleObject(process_info.hProcess, INFINITE);
if(!GetExitCodeProcess(process_info.hProcess, (DWORD*) &RetCode))
RetCode = -1;
CloseHandle(process_info.hProcess);
if(stdout_thread.joinable())
stdout_thread.join();
if(stderr_thread.joinable())
stderr_thread.join();
CloseHandle(stdout_rd);
CloseHandle(stderr_rd);
return 0;
}
int main()
{
int rc;
uint32_t RetCode;
string ListStdOut;
string ListStdErr;
cout << "STARTING.\n";
rc = SystemCapture(
"C:\\Windows\\System32\\ipconfig.exe", //Command Line
".", //CmdRunDir
ListStdOut, //Return List of StdOut
ListStdErr, //Return List of StdErr
RetCode //Return Exit Code
);
if (rc < 0) {
cout << "ERROR: SystemCapture\n";
}
cout << "STDOUT:\n";
cout << ListStdOut;
cout << "STDERR:\n";
cout << ListStdErr;
cout << "Finished.\n";
cout << "Press Enter to Continue";
cin.ignore();
return 0;
}
Take note that you can get output by redirecting output to the file and then reading it
It was shown in documentation of std::system
You can receive exit code by calling WEXITSTATUS macro.
int status = std::system("ls -l >test.txt"); // execute the UNIX command "ls -l >test.txt"
std::cout << std::ifstream("test.txt").rdbuf();
std::cout << "Exit code: " << WEXITSTATUS(status) << std::endl;
Assuming POSIX, simple code to capture stdout:
#include <sys/wait.h>
#include <unistd.h>
#include <string>
#include <vector>
std::string qx(const std::vector<std::string>& args) {
int stdout_fds[2];
pipe(stdout_fds);
int stderr_fds[2];
pipe(stderr_fds);
const pid_t pid = fork();
if (!pid) {
close(stdout_fds[0]);
dup2(stdout_fds[1], 1);
close(stdout_fds[1]);
close(stderr_fds[0]);
dup2(stderr_fds[1], 2);
close(stderr_fds[1]);
std::vector<char*> vc(args.size() + 1, 0);
for (size_t i = 0; i < args.size(); ++i) {
vc[i] = const_cast<char*>(args[i].c_str());
}
execvp(vc[0], &vc[0]);
exit(0);
}
close(stdout_fds[1]);
std::string out;
const int buf_size = 4096;
char buffer[buf_size];
do {
const ssize_t r = read(stdout_fds[0], buffer, buf_size);
if (r > 0) {
out.append(buffer, r);
}
} while (errno == EAGAIN || errno == EINTR);
close(stdout_fds[0]);
close(stderr_fds[1]);
close(stderr_fds[0]);
int r, status;
do {
r = waitpid(pid, &status, 0);
} while (r == -1 && errno == EINTR);
return out;
}
Code contributions are welcome for more functionality:
https://github.com/ericcurtin/execxx
You can get the output after running a script using a pipe. We use pipes when we want the output of the child process.
int my_func() {
char ch;
FILE *fpipe;
FILE *copy_fp;
FILE *tmp;
char *command = (char *)"/usr/bin/my_script my_arg";
copy_fp = fopen("/tmp/output_file_path", "w");
fpipe = (FILE *)popen(command, "r");
if (fpipe) {
while ((ch = fgetc(fpipe)) != EOF) {
fputc(ch, copy_fp);
}
}
else {
if (copy_fp) {
fprintf(copy_fp, "Sorry there was an error opening the file");
}
}
pclose(fpipe);
fclose(copy_fp);
return 0;
}
So here is the script, which you want to run. Put it in a command variable with the arguments your script takes (nothing if no arguments). And the file where you want to capture the output of the script, put it in copy_fp.
So the popen runs your script and puts the output in fpipe and then you can just copy everything from that to your output file.
In this way you can capture the outputs of child processes.
And another process is you can directly put the > operator in the command only. So if we will put everything in a file while we run the command, you won't have to copy anything.
In that case, there isn't any need to use pipes. You can use just system, and it will run the command and put the output in that file.
int my_func(){
char *command = (char *)"/usr/bin/my_script my_arg > /tmp/my_putput_file";
system(command);
printf("everything saved in my_output_file");
return 0;
}
You can read YoLinux Tutorial: Fork, Exec and Process control for more information.
Command class uses system("cmd > stdout 2> stderr") to provide user with stdout and stderr, in addition to the exit code.
Test run:
./a.out 'ls .'
exit code: 0
stdout: HelloWorld
HelloWorld.c
HelloWorld.cpp
HelloWorld.dSYM
a.out
gcc_container.bash
linuxsys
macsys
test.sh
stderr:
#include <iostream>
#include <fstream>
#include <sstream>
#include <unistd.h>
using namespace std;
class Command {
public:
Command() {
exit_code_ = -1;
}
int GetExitCode() { return exit_code_;}
string GetStdOutStr() {return stdout_str_;}
string GetStdErrStr() {return stderr_str_;}
int Run(const char* cmd) {
return Run(string(cmd));
}
/**
* #brief run a given command
*
* #param cmd: command string
* #return int: the exit code of running the command
*/
int Run(string cmd) {
// create temp files
char tmp_dir[] = "/tmp/stdir.XXXXXX";
mkdtemp(tmp_dir);
string stdout_file = string(tmp_dir) + "/stdout";
string stderr_file = string(tmp_dir) + "/stderr";
// execute the command "cmd > stdout_file 2> stderr_file"
string cli = cmd + " > " + stdout_file + " 2> " + stderr_file;
exit_code_ = system(cli.c_str());
exit_code_ = WEXITSTATUS(exit_code_);
stdout_str_ = File2Str(stdout_file);
stderr_str_ = File2Str(stderr_file);
// rid of the temp files
remove(stdout_file.c_str());
remove(stderr_file.c_str());
remove(tmp_dir);
return exit_code_;
}
private:
int exit_code_;
string stderr_str_;
string stdout_str_;
/**
* #brief read a file
*
* #param file_name: file path
* #return string the contents of the file.
*/
string File2Str(string file_name) {
ifstream file;
stringstream str_stream;
file.open(file_name);
if (file.is_open()) {
str_stream << file.rdbuf();
file.close();
}
return str_stream.str();
}
};
int main(int argc, const char* argv[]) {
Command command;
command.Run(argv[1]);
cout << "exit code: " << command.GetExitCode() << endl;
cout << "stdout: " << command.GetStdOutStr() << endl;
cout << "stderr: " << command.GetStdErrStr() << endl;
return command.GetExitCode();
}
C++ stream implemention of waqas's answer:
#include <istream>
#include <streambuf>
#include <cstdio>
#include <cstring>
#include <memory>
#include <stdexcept>
#include <string>
class execbuf : public std::streambuf {
protected:
std::string output;
int_type underflow(int_type character) {
if (gptr() < egptr()) return traits_type::to_int_type(*gptr());
return traits_type::eof();
}
public:
execbuf(const char* command) {
std::array<char, 128> buffer;
std::unique_ptr<FILE, decltype(&pclose)> pipe(popen(command, "r"), pclose);
if (!pipe) {
throw std::runtime_error("popen() failed!");
}
while (fgets(buffer.data(), buffer.size(), pipe.get()) != nullptr) {
this->output += buffer.data();
}
setg((char*)this->output.data(), (char*)this->output.data(), (char*)(this->output.data() + this->output.size()));
}
};
class exec : public std::istream {
protected:
execbuf buffer;
public:
exec(char* command) : std::istream(nullptr), buffer(command, fd) {
this->rdbuf(&buffer);
}
};
This code catches all output through stdout . If you want to catch only stderr then pass your command like this:
sh -c '<your-command>' 2>&1 > /dev/null
If you want to catch both stdout and stderr then the command should be like this:
sh -c '<your-command>' 2>&1
I am trying to create a microshell. It reads commands in, parses this and splits this, then executes. To parse, first I separate by the delimiter || to get up to two commands if there is a pipe. The split each command into an array of strings.
I thought this is how execlp works, but it only runs the command even though the C string "cmd1" does contain the arguments. Can someone please help me understand how I am passing the parameters wrong to the execlp function?
shell.h
/****************************************************************
PROGRAM: MicroShell(assignment 4)
FILE: shell.h
AUTHOR: Nick Schuck
FUNCTION: This contains the header for the shell class
****************************************************************/
#ifndef _shell_h
#define _shell_h
#include <sys/types.h>
#include <unistd.h>
#include <cstdio>
#include <pwd.h>
#include <cstring>
#include <sys/wait.h>
#include <cstdlib>
#include <vector>
class Shell
{
private:
char buffer[1024];
const char *cmd1[10];
const char *cmd2[10];
public:
Shell(); //default constructor
void askForCommand();
void readCommandLine();
void parseBuffer();
void invokeCommand();
void executeOneCommand();
void executeTwoCommands();
};
#endif
shell.cc
/***************************************************************
PROGRAM: MicroShell(assignment 4)
FILE: shell.c
AUTHOR: Nick Schuck
FUNCTION: This file contains the implementation of
class shell from file "shell.h"
****************************************************************/
#include "shell.h"
#include <iostream>
Shell::Shell()
{
/**Get current user*/
struct passwd *p = getpwuid(getuid());
if (!p) //Error handling
puts("Welcome to Nick Schuck's MicroShell, Anonymous");
/**Welcome message for my shell*/
printf("\n\nWelcome to Nick Schuck's Microshell, user %s!\n\n", p->pw_name);
}
void Shell::askForCommand()
{
/**Command Prompt*/
printf("myshell>");
}
void Shell::readCommandLine()
{
/**Read stdin into buffer array IF no*/
/**errors occur */
if (fgets(this->buffer, 1024, stdin) != NULL)
{
this->buffer[strlen(this->buffer) - 1] = 0;
}
}
void Shell::parseBuffer()
{
/**Variables*/
int i = 0, u = 0,
t = 0;
char *ptr;
char parsingBuffer[2][512];
/**Parse buffer for multiple commands*/
strcpy(parsingBuffer[0], strtok(this->buffer, "||"));
while ((ptr = strtok(NULL, "||")) != NULL)
{
i++;
strcpy(parsingBuffer[i], ptr);
}
//**Get first command*/
this->cmd1[0] = strtok(parsingBuffer[0], " ");
while ((ptr = strtok(NULL, " ")) != NULL)
{
u++;
this->cmd1[u] = ptr;
this->cmd1[u+1] = '\0';
}
//!!!TESTING TO SEE COMMAND ARE IN CMD1
int b = 0;
while(cmd1[b] != '\0')
{
std::cout << cmd1[b] << "\n";
b++;
}
/**Get second command*/
this->cmd2[0] = strtok(parsingBuffer[1], " ");
while ((ptr = strtok(NULL, " ")) != NULL)
{
t++;
this->cmd2[t] = ptr;
}
}
void Shell::invokeCommand()
{
if (this->cmd1[0] == NULL)
{
//do nothing
}
else if(this->cmd1[0] != NULL && this->cmd2[0] == NULL)
{
executeOneCommand();
}
else if(this->cmd1[0] != NULL && cmd2[0] !=NULL)
{
executeTwoCommands();
}
}
void Shell::executeOneCommand()
{
pid_t pid; //pid for fork
int status;
char args[512];
if ((pid = fork()) < 0)
{
printf("fork error\n");
exit(-1);
}
else if(pid == 0) //Child Process
{
execlp(cmd1[0], *cmd1);
}
else //Parent Process
{
if ((pid = waitpid(pid, &status, 0)) < 0)
{
printf("waitpid error in main\n");
exit(-1);
}
}
}
main.cc
#include "shell.h"
#include <iostream>
#include <vector>
int main()
{
const int BUFFER_SIZE = 1024;
const int MAX_COMMANDS_IN_BUFFER = 2;
/**Initialize a new shell object*/
Shell shell;
/**Print command prompt to screen*/
shell.askForCommand();
/**Read users command*/
shell.readCommandLine();
/**parse buffer to find individual*/
/**commands */
shell.parseBuffer();
/**Invoke command*/
shell.invokeCommand();
}
You can't use execlp() — you must use execvp().
execvp(cmd1[0], cmd1);
To use execlp(), you must know at compile time the fixed list of arguments for the command — you must be able to write:
execlp(cmd_name, arg0, arg1, …, argN, (char *)0);
Your call to execlp() is also faulty because you don't provide the (char *)0 argument to indicate the end of the argument list.
Your code also needs to handle exec*() returning, which means the command failed. Usually that means it should print an error message (that the command was not found, or permission denied, or whatever), and then exit with an appropriate non-zero error status.
I am working in Ubuntu. I want to monitor a folder and print every event that pops up in the subfolders (print files).
I have the following code but it doesn't work. When executed, there is no println of the events.
In the second code I only see the events from the folder. The events from each subfolder do not pop up.
#include <string>
#include <iostream>
#include <stdio.h>
using namespace std;
std::string exec(char* cmd) {
FILE* pipe = popen(cmd, "r");
if (!pipe) return "ERROR";
char buffer[256];
std::string result = "";
while(!feof(pipe)) {
if(fgets(buffer, 256, pipe) != NULL)
result += buffer;
}
pclose(pipe);
cout<<"result is: "<<result<<endl;
return result;
}
int main()
{
//while(1)
//{
string s=exec((char*)"inotifywait -rme create /home/folder/");
cout << s << endl;
//}
return 0;
}
This code only prints the events from the folder I'm monitoring. It doesn't print the events from each subfolder. I don't know how to improve it for my needs.
#include <sys/inotify.h>
#include <sys/ioctl.h>
#include <iostream>
void processNewFiles(int fd, int wd);
int main(int argc, char** argv)
{
const char* dirPath = "/home/folder/" ;//argv[1];
int fd = inotify_init();
int wd = inotify_add_watch(fd, dirPath, IN_CREATE);
if (wd)
{
processNewFiles(fd, wd);
inotify_rm_watch(fd, wd);
}
}
void processNewFiles(int fd, int wd)
{
bool done = false;
do
{
int qLen = 0;
ioctl(fd, FIONREAD, &qLen);
char* buf = new char[qLen];
int num = read(fd, buf, qLen);
if (num == qLen)
{
inotify_event* iev = reinterpret_cast<inotify_event*>(buf);
if (iev->wd == wd && iev->mask & IN_CREATE)
{
std::cout << "New file created: " << iev->name << std::endl;
}
}
delete [] buf;
} while (!done);
}
Your second solution does not work because inotify_add_watch is not working recursivly. You would have to add watches for subdirectories manually. As this might be annoying, it is also possible to use the utility inotifywait as you do in your first example.
Your first example is not working because you're reading from the pipe forever. If you kill the inotifywait process (e.g. if you're the only person on the machine and this is the only inotifywait process just using "killall inotifywait") you will get your output because you'll break out of the loop reading from the pipe. If you output something inside the loop, it will work, too.
I am looking for a way to get the output of a command when it is run from within a C++ program. I have looked at using the system() function, but that will just execute a command. Here's an example of what I'm looking for:
std::string result = system("./some_command");
I need to run an arbitrary command and get its output. I've looked at boost.org, but I have not found anything that will give me what I need.
#include <cstdio>
#include <iostream>
#include <memory>
#include <stdexcept>
#include <string>
#include <array>
std::string exec(const char* cmd) {
std::array<char, 128> buffer;
std::string result;
std::unique_ptr<FILE, decltype(&pclose)> pipe(popen(cmd, "r"), pclose);
if (!pipe) {
throw std::runtime_error("popen() failed!");
}
while (fgets(buffer.data(), buffer.size(), pipe.get()) != nullptr) {
result += buffer.data();
}
return result;
}
Pre-C++11 version:
#include <iostream>
#include <stdexcept>
#include <stdio.h>
#include <string>
std::string exec(const char* cmd) {
char buffer[128];
std::string result = "";
FILE* pipe = popen(cmd, "r");
if (!pipe) throw std::runtime_error("popen() failed!");
try {
while (fgets(buffer, sizeof buffer, pipe) != NULL) {
result += buffer;
}
} catch (...) {
pclose(pipe);
throw;
}
pclose(pipe);
return result;
}
Replace popen and pclose with _popen and _pclose for Windows.
Getting both stdout and stderr (and also writing to stdin, not shown here) is easy peasy with my pstreams header, which defines iostream classes that work like popen:
#include <pstream.h>
#include <string>
#include <iostream>
int main()
{
// run a process and create a streambuf that reads its stdout and stderr
redi::ipstream proc("./some_command", redi::pstreams::pstdout | redi::pstreams::pstderr);
std::string line;
// read child's stdout
while (std::getline(proc.out(), line))
std::cout << "stdout: " << line << '\n';
// if reading stdout stopped at EOF then reset the state:
if (proc.eof() && proc.fail())
proc.clear();
// read child's stderr
while (std::getline(proc.err(), line))
std::cout << "stderr: " << line << '\n';
}
For Windows, popen also works, but it opens up a console window - which quickly flashes over your UI application. If you want to be a professional, it's better to disable this "flashing" (especially if the end-user can cancel it).
So here is my own version for Windows:
(This code is partially recombined from ideas written in The Code Project and MSDN samples.)
#include <windows.h>
#include <atlstr.h>
//
// Execute a command and get the results. (Only standard output)
//
CStringA ExecCmd(
const wchar_t* cmd // [in] command to execute
)
{
CStringA strResult;
HANDLE hPipeRead, hPipeWrite;
SECURITY_ATTRIBUTES saAttr = {sizeof(SECURITY_ATTRIBUTES)};
saAttr.bInheritHandle = TRUE; // Pipe handles are inherited by child process.
saAttr.lpSecurityDescriptor = NULL;
// Create a pipe to get results from child's stdout.
if (!CreatePipe(&hPipeRead, &hPipeWrite, &saAttr, 0))
return strResult;
STARTUPINFOW si = {sizeof(STARTUPINFOW)};
si.dwFlags = STARTF_USESHOWWINDOW | STARTF_USESTDHANDLES;
si.hStdOutput = hPipeWrite;
si.hStdError = hPipeWrite;
si.wShowWindow = SW_HIDE; // Prevents cmd window from flashing.
// Requires STARTF_USESHOWWINDOW in dwFlags.
PROCESS_INFORMATION pi = { 0 };
BOOL fSuccess = CreateProcessW(NULL, (LPWSTR)cmd, NULL, NULL, TRUE, CREATE_NEW_CONSOLE, NULL, NULL, &si, &pi);
if (! fSuccess)
{
CloseHandle(hPipeWrite);
CloseHandle(hPipeRead);
return strResult;
}
bool bProcessEnded = false;
for (; !bProcessEnded ;)
{
// Give some timeslice (50 ms), so we won't waste 100% CPU.
bProcessEnded = WaitForSingleObject( pi.hProcess, 50) == WAIT_OBJECT_0;
// Even if process exited - we continue reading, if
// there is some data available over pipe.
for (;;)
{
char buf[1024];
DWORD dwRead = 0;
DWORD dwAvail = 0;
if (!::PeekNamedPipe(hPipeRead, NULL, 0, NULL, &dwAvail, NULL))
break;
if (!dwAvail) // No data available, return
break;
if (!::ReadFile(hPipeRead, buf, min(sizeof(buf) - 1, dwAvail), &dwRead, NULL) || !dwRead)
// Error, the child process might ended
break;
buf[dwRead] = 0;
strResult += buf;
}
} //for
CloseHandle(hPipeWrite);
CloseHandle(hPipeRead);
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
return strResult;
} //ExecCmd
I'd use popen() (++waqas).
But sometimes you need reading and writing...
It seems like nobody does things the hard way any more.
(Assuming a Unix/Linux/Mac environment, or perhaps Windows with a POSIX compatibility layer...)
enum PIPE_FILE_DESCRIPTERS
{
READ_FD = 0,
WRITE_FD = 1
};
enum CONSTANTS
{
BUFFER_SIZE = 100
};
int
main()
{
int parentToChild[2];
int childToParent[2];
pid_t pid;
string dataReadFromChild;
char buffer[BUFFER_SIZE + 1];
ssize_t readResult;
int status;
ASSERT_IS(0, pipe(parentToChild));
ASSERT_IS(0, pipe(childToParent));
switch (pid = fork())
{
case -1:
FAIL("Fork failed");
exit(-1);
case 0: /* Child */
ASSERT_NOT(-1, dup2(parentToChild[READ_FD], STDIN_FILENO));
ASSERT_NOT(-1, dup2(childToParent[WRITE_FD], STDOUT_FILENO));
ASSERT_NOT(-1, dup2(childToParent[WRITE_FD], STDERR_FILENO));
ASSERT_IS(0, close(parentToChild [WRITE_FD]));
ASSERT_IS(0, close(childToParent [READ_FD]));
/* file, arg0, arg1, arg2 */
execlp("ls", "ls", "-al", "--color");
FAIL("This line should never be reached!!!");
exit(-1);
default: /* Parent */
cout << "Child " << pid << " process running..." << endl;
ASSERT_IS(0, close(parentToChild [READ_FD]));
ASSERT_IS(0, close(childToParent [WRITE_FD]));
while (true)
{
switch (readResult = read(childToParent[READ_FD],
buffer, BUFFER_SIZE))
{
case 0: /* End-of-File, or non-blocking read. */
cout << "End of file reached..." << endl
<< "Data received was ("
<< dataReadFromChild.size() << "): " << endl
<< dataReadFromChild << endl;
ASSERT_IS(pid, waitpid(pid, & status, 0));
cout << endl
<< "Child exit staus is: " << WEXITSTATUS(status) << endl
<< endl;
exit(0);
case -1:
if ((errno == EINTR) || (errno == EAGAIN))
{
errno = 0;
break;
}
else
{
FAIL("read() failed");
exit(-1);
}
default:
dataReadFromChild . append(buffer, readResult);
break;
}
} /* while (true) */
} /* switch (pid = fork())*/
}
You also might want to play around with select() and non-blocking reads.
fd_set readfds;
struct timeval timeout;
timeout.tv_sec = 0; /* Seconds */
timeout.tv_usec = 1000; /* Microseconds */
FD_ZERO(&readfds);
FD_SET(childToParent[READ_FD], &readfds);
switch (select (1 + childToParent[READ_FD], &readfds, (fd_set*)NULL, (fd_set*)NULL, & timeout))
{
case 0: /* Timeout expired */
break;
case -1:
if ((errno == EINTR) || (errno == EAGAIN))
{
errno = 0;
break;
}
else
{
FAIL("Select() Failed");
exit(-1);
}
case 1: /* We have input */
readResult = read(childToParent[READ_FD], buffer, BUFFER_SIZE);
// However you want to handle it...
break;
default:
FAIL("How did we see input on more than one file descriptor?");
exit(-1);
}
Two possible approaches:
I don't think popen() is part of the C++ standard (it's part of POSIX from memory), but it's available on every UNIX I've worked with (and you seem to be targeting UNIX since your command is ./some_command).
On the off-chance that there is no popen(), you can use system("./some_command >/tmp/some_command.out");, then use the normal I/O functions to process the output file.
The following might be a portable solution. It follows standards.
#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
#include <sstream>
std::string ssystem (const char *command) {
char tmpname [L_tmpnam];
std::tmpnam ( tmpname );
std::string scommand = command;
std::string cmd = scommand + " >> " + tmpname;
std::system(cmd.c_str());
std::ifstream file(tmpname, std::ios::in | std::ios::binary );
std::string result;
if (file) {
while (!file.eof()) result.push_back(file.get())
;
file.close();
}
remove(tmpname);
return result;
}
// For Cygwin
int main(int argc, char *argv[])
{
std::string bash = "FILETWO=/cygdrive/c/*\nfor f in $FILETWO\ndo\necho \"$f\"\ndone ";
std::string in;
std::string s = ssystem(bash.c_str());
std::istringstream iss(s);
std::string line;
while (std::getline(iss, line))
{
std::cout << "LINE-> " + line + " length: " << line.length() << std::endl;
}
std::cin >> in;
return 0;
}
I couldn't figure out why popen/pclose is missing from Code::Blocks/MinGW. So I worked around the problem by using CreateProcess() and CreatePipe() instead.
Here's the solution that worked for me:
//C++11
#include <cstdio>
#include <iostream>
#include <windows.h>
#include <cstdint>
#include <deque>
#include <string>
#include <thread>
using namespace std;
int SystemCapture(
string CmdLine, //Command Line
string CmdRunDir, //set to '.' for current directory
string& ListStdOut, //Return List of StdOut
string& ListStdErr, //Return List of StdErr
uint32_t& RetCode) //Return Exit Code
{
int Success;
SECURITY_ATTRIBUTES security_attributes;
HANDLE stdout_rd = INVALID_HANDLE_VALUE;
HANDLE stdout_wr = INVALID_HANDLE_VALUE;
HANDLE stderr_rd = INVALID_HANDLE_VALUE;
HANDLE stderr_wr = INVALID_HANDLE_VALUE;
PROCESS_INFORMATION process_info;
STARTUPINFO startup_info;
thread stdout_thread;
thread stderr_thread;
security_attributes.nLength = sizeof(SECURITY_ATTRIBUTES);
security_attributes.bInheritHandle = TRUE;
security_attributes.lpSecurityDescriptor = nullptr;
if (!CreatePipe(&stdout_rd, &stdout_wr, &security_attributes, 0) ||
!SetHandleInformation(stdout_rd, HANDLE_FLAG_INHERIT, 0)) {
return -1;
}
if (!CreatePipe(&stderr_rd, &stderr_wr, &security_attributes, 0) ||
!SetHandleInformation(stderr_rd, HANDLE_FLAG_INHERIT, 0)) {
if (stdout_rd != INVALID_HANDLE_VALUE) CloseHandle(stdout_rd);
if (stdout_wr != INVALID_HANDLE_VALUE) CloseHandle(stdout_wr);
return -2;
}
ZeroMemory(&process_info, sizeof(PROCESS_INFORMATION));
ZeroMemory(&startup_info, sizeof(STARTUPINFO));
startup_info.cb = sizeof(STARTUPINFO);
startup_info.hStdInput = 0;
startup_info.hStdOutput = stdout_wr;
startup_info.hStdError = stderr_wr;
if(stdout_rd || stderr_rd)
startup_info.dwFlags |= STARTF_USESTDHANDLES;
// Make a copy because CreateProcess needs to modify string buffer
char CmdLineStr[MAX_PATH];
strncpy(CmdLineStr, CmdLine.c_str(), MAX_PATH);
CmdLineStr[MAX_PATH-1] = 0;
Success = CreateProcess(
nullptr,
CmdLineStr,
nullptr,
nullptr,
TRUE,
0,
nullptr,
CmdRunDir.c_str(),
&startup_info,
&process_info
);
CloseHandle(stdout_wr);
CloseHandle(stderr_wr);
if(!Success) {
CloseHandle(process_info.hProcess);
CloseHandle(process_info.hThread);
CloseHandle(stdout_rd);
CloseHandle(stderr_rd);
return -4;
}
else {
CloseHandle(process_info.hThread);
}
if(stdout_rd) {
stdout_thread=thread([&]() {
DWORD n;
const size_t bufsize = 1000;
char buffer [bufsize];
for(;;) {
n = 0;
int Success = ReadFile(
stdout_rd,
buffer,
(DWORD)bufsize,
&n,
nullptr
);
printf("STDERR: Success:%d n:%d\n", Success, (int)n);
if(!Success || n == 0)
break;
string s(buffer, n);
printf("STDOUT:(%s)\n", s.c_str());
ListStdOut += s;
}
printf("STDOUT:BREAK!\n");
});
}
if(stderr_rd) {
stderr_thread=thread([&]() {
DWORD n;
const size_t bufsize = 1000;
char buffer [bufsize];
for(;;) {
n = 0;
int Success = ReadFile(
stderr_rd,
buffer,
(DWORD)bufsize,
&n,
nullptr
);
printf("STDERR: Success:%d n:%d\n", Success, (int)n);
if(!Success || n == 0)
break;
string s(buffer, n);
printf("STDERR:(%s)\n", s.c_str());
ListStdErr += s;
}
printf("STDERR:BREAK!\n");
});
}
WaitForSingleObject(process_info.hProcess, INFINITE);
if(!GetExitCodeProcess(process_info.hProcess, (DWORD*) &RetCode))
RetCode = -1;
CloseHandle(process_info.hProcess);
if(stdout_thread.joinable())
stdout_thread.join();
if(stderr_thread.joinable())
stderr_thread.join();
CloseHandle(stdout_rd);
CloseHandle(stderr_rd);
return 0;
}
int main()
{
int rc;
uint32_t RetCode;
string ListStdOut;
string ListStdErr;
cout << "STARTING.\n";
rc = SystemCapture(
"C:\\Windows\\System32\\ipconfig.exe", //Command Line
".", //CmdRunDir
ListStdOut, //Return List of StdOut
ListStdErr, //Return List of StdErr
RetCode //Return Exit Code
);
if (rc < 0) {
cout << "ERROR: SystemCapture\n";
}
cout << "STDOUT:\n";
cout << ListStdOut;
cout << "STDERR:\n";
cout << ListStdErr;
cout << "Finished.\n";
cout << "Press Enter to Continue";
cin.ignore();
return 0;
}
Take note that you can get output by redirecting output to the file and then reading it
It was shown in documentation of std::system
You can receive exit code by calling WEXITSTATUS macro.
int status = std::system("ls -l >test.txt"); // execute the UNIX command "ls -l >test.txt"
std::cout << std::ifstream("test.txt").rdbuf();
std::cout << "Exit code: " << WEXITSTATUS(status) << std::endl;
Assuming POSIX, simple code to capture stdout:
#include <sys/wait.h>
#include <unistd.h>
#include <string>
#include <vector>
std::string qx(const std::vector<std::string>& args) {
int stdout_fds[2];
pipe(stdout_fds);
int stderr_fds[2];
pipe(stderr_fds);
const pid_t pid = fork();
if (!pid) {
close(stdout_fds[0]);
dup2(stdout_fds[1], 1);
close(stdout_fds[1]);
close(stderr_fds[0]);
dup2(stderr_fds[1], 2);
close(stderr_fds[1]);
std::vector<char*> vc(args.size() + 1, 0);
for (size_t i = 0; i < args.size(); ++i) {
vc[i] = const_cast<char*>(args[i].c_str());
}
execvp(vc[0], &vc[0]);
exit(0);
}
close(stdout_fds[1]);
std::string out;
const int buf_size = 4096;
char buffer[buf_size];
do {
const ssize_t r = read(stdout_fds[0], buffer, buf_size);
if (r > 0) {
out.append(buffer, r);
}
} while (errno == EAGAIN || errno == EINTR);
close(stdout_fds[0]);
close(stderr_fds[1]);
close(stderr_fds[0]);
int r, status;
do {
r = waitpid(pid, &status, 0);
} while (r == -1 && errno == EINTR);
return out;
}
Code contributions are welcome for more functionality:
https://github.com/ericcurtin/execxx
You can get the output after running a script using a pipe. We use pipes when we want the output of the child process.
int my_func() {
char ch;
FILE *fpipe;
FILE *copy_fp;
FILE *tmp;
char *command = (char *)"/usr/bin/my_script my_arg";
copy_fp = fopen("/tmp/output_file_path", "w");
fpipe = (FILE *)popen(command, "r");
if (fpipe) {
while ((ch = fgetc(fpipe)) != EOF) {
fputc(ch, copy_fp);
}
}
else {
if (copy_fp) {
fprintf(copy_fp, "Sorry there was an error opening the file");
}
}
pclose(fpipe);
fclose(copy_fp);
return 0;
}
So here is the script, which you want to run. Put it in a command variable with the arguments your script takes (nothing if no arguments). And the file where you want to capture the output of the script, put it in copy_fp.
So the popen runs your script and puts the output in fpipe and then you can just copy everything from that to your output file.
In this way you can capture the outputs of child processes.
And another process is you can directly put the > operator in the command only. So if we will put everything in a file while we run the command, you won't have to copy anything.
In that case, there isn't any need to use pipes. You can use just system, and it will run the command and put the output in that file.
int my_func(){
char *command = (char *)"/usr/bin/my_script my_arg > /tmp/my_putput_file";
system(command);
printf("everything saved in my_output_file");
return 0;
}
You can read YoLinux Tutorial: Fork, Exec and Process control for more information.
Command class uses system("cmd > stdout 2> stderr") to provide user with stdout and stderr, in addition to the exit code.
Test run:
./a.out 'ls .'
exit code: 0
stdout: HelloWorld
HelloWorld.c
HelloWorld.cpp
HelloWorld.dSYM
a.out
gcc_container.bash
linuxsys
macsys
test.sh
stderr:
#include <iostream>
#include <fstream>
#include <sstream>
#include <unistd.h>
using namespace std;
class Command {
public:
Command() {
exit_code_ = -1;
}
int GetExitCode() { return exit_code_;}
string GetStdOutStr() {return stdout_str_;}
string GetStdErrStr() {return stderr_str_;}
int Run(const char* cmd) {
return Run(string(cmd));
}
/**
* #brief run a given command
*
* #param cmd: command string
* #return int: the exit code of running the command
*/
int Run(string cmd) {
// create temp files
char tmp_dir[] = "/tmp/stdir.XXXXXX";
mkdtemp(tmp_dir);
string stdout_file = string(tmp_dir) + "/stdout";
string stderr_file = string(tmp_dir) + "/stderr";
// execute the command "cmd > stdout_file 2> stderr_file"
string cli = cmd + " > " + stdout_file + " 2> " + stderr_file;
exit_code_ = system(cli.c_str());
exit_code_ = WEXITSTATUS(exit_code_);
stdout_str_ = File2Str(stdout_file);
stderr_str_ = File2Str(stderr_file);
// rid of the temp files
remove(stdout_file.c_str());
remove(stderr_file.c_str());
remove(tmp_dir);
return exit_code_;
}
private:
int exit_code_;
string stderr_str_;
string stdout_str_;
/**
* #brief read a file
*
* #param file_name: file path
* #return string the contents of the file.
*/
string File2Str(string file_name) {
ifstream file;
stringstream str_stream;
file.open(file_name);
if (file.is_open()) {
str_stream << file.rdbuf();
file.close();
}
return str_stream.str();
}
};
int main(int argc, const char* argv[]) {
Command command;
command.Run(argv[1]);
cout << "exit code: " << command.GetExitCode() << endl;
cout << "stdout: " << command.GetStdOutStr() << endl;
cout << "stderr: " << command.GetStdErrStr() << endl;
return command.GetExitCode();
}
C++ stream implemention of waqas's answer:
#include <istream>
#include <streambuf>
#include <cstdio>
#include <cstring>
#include <memory>
#include <stdexcept>
#include <string>
class execbuf : public std::streambuf {
protected:
std::string output;
int_type underflow(int_type character) {
if (gptr() < egptr()) return traits_type::to_int_type(*gptr());
return traits_type::eof();
}
public:
execbuf(const char* command) {
std::array<char, 128> buffer;
std::unique_ptr<FILE, decltype(&pclose)> pipe(popen(command, "r"), pclose);
if (!pipe) {
throw std::runtime_error("popen() failed!");
}
while (fgets(buffer.data(), buffer.size(), pipe.get()) != nullptr) {
this->output += buffer.data();
}
setg((char*)this->output.data(), (char*)this->output.data(), (char*)(this->output.data() + this->output.size()));
}
};
class exec : public std::istream {
protected:
execbuf buffer;
public:
exec(char* command) : std::istream(nullptr), buffer(command, fd) {
this->rdbuf(&buffer);
}
};
This code catches all output through stdout . If you want to catch only stderr then pass your command like this:
sh -c '<your-command>' 2>&1 > /dev/null
If you want to catch both stdout and stderr then the command should be like this:
sh -c '<your-command>' 2>&1