C程序中grep命令的异常行为

Question

Consider the following two text files:

def.txt

simple =
"sik", /* fill */
"trauma", /* type */
"hui", /* col */

def.dat

simple =
"sik", /* fill */
"trauma", /* type */
"hui", /* col */

The above 2 files are stored in examples directory.

The following grep command works fine as expected:

$ grep --include=*.{txt,dat} -rnw example/ -F -e 'simple'
example/def.dat:1:simple =
example/def.txt:1:simple =
$ echo $? => 0

But when I execute the above grep command in C program:

#include <stdio.h>
#include <string.h>

int main (void)
{
  char cmd[1024];

  strcpy (cmd, "grep --include=*.{txt,dat} -rnw example/ -F -e 'simple'");
  printf ("%d\n", system (cmd));
  return 0;
}

The output of the above program is 256 .

Answer 1

/bin/sh is not bash. /bin/sh does not support brace expansions. Try running that command through /bin/sh manually and it won't work either.

Your choices are to write out the command manually (do the brace expansion yourself) or wrap your command in /bin/bash -c '......' and ensure you've provided enough quote escaping to keep your desired command intact that way (which is complicated and ugly).

The other option is to not do this at all. Either by using a script that you execute (with an appropriate shebang line) or (better) by finding native solutions to the task you need to solve.