In C on Linux, popen / system to "ps all > file" truncates all lines to 80 characters

c, c++, linux, system, ubuntu

Solution

As a workaround, try passing `-w` or possibly `-ww` to `ps` when you invoke it.

From the man page (BSD):

-w      Use 132 columns to display information, instead of the default which is your 
        window size.  If the -w option is specified more than once, ps will use as many
        columns as necessary without regard for your window size.  When output is
        not to a terminal, an unlimited number of columns are always used.

Linux:

-w      Wide output. Use this option twice for unlimited width.

Alternatively,

You might have some success doing a `fork/exec/wait` yourself instead of using `system`; omitting error handling for brevity:

#include <unistd.h>
#include <stdio.h>

pid_t pid = fork();

if (!pid) {
   /* child */
   FILE* fp = fopen("./your-file", "w");
   close(STDOUT_FILENO);
   dup2(fileno(fp), STDOUT_FILENO);
   execlp("ps", "ps", "all", (char*)NULL);
} else {
  /* parent */
  int status;
  wait(&status);
  printf("ps exited with status %d\n", status);
}

Problem

I'm using Ubuntu 11.10. If I open a terminal and call: `ps all` I get the results truncated (i.e. 100 characters at most for each line) to the size of the terminal window. If I call `ps all > file` The lines don't get truncated and all the information is in the file (There is a line that has ~200 characters) In C, I am trying to achieve the same but the lines get truncated. I've tried `int rc = system("ps all > file");` as well as variants of popen. I assume the shell being used by system (and popen) defaults the output of each line to 80, which make sense if I were to parse it using popen, but since I am piping it to a file I expect it to disregard the size of the shell like I experienced when doing it in my shell. TL;DR How can I make sure `ps all > file` doesn't truncate lines when called from C application?

Original source