Difficulty in passing command line arguments

Question

I want to pass command line to my c program by reading another file using cat command as follows:

cat data | ./file

contents of the file data are

abc def ghi jkl mno pqr stu vwx yz

and code of the file.c is

#include <stdio.h>

int main( int args, char * argv[] )
{
     int i = 0;
     for( i; i < args; i++ )
     {
         printf(argv[i]);
         printf("\n");
     }
}

when the code is run as follows

cat a | ./file

it just display the file name and don't display the a contents. Am I doing it right?

score 2 · Answer 1 · answered Apr 18 '15 at 07:18

2

You should try something like:

./file $(cat a)

answered Apr 18 '15 at 07:18

SMA

36,381
8
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In this way, it works fine. but I want to do in the above-mentioned way. – HAMAD MAHMOOD Apr 18 '15 at 07:21

score 2 · Answer 2 · answered Apr 18 '15 at 07:35

2

The pipe is treated as STDIN fd instead of command line arguments.

You may need cat a | xargs ./file.

leetom@leetoms-MBP:~$ cat aa.txt
aaa bbb cc
leetom@leetoms-MBP:~$ cat aa.txt | xargs ./a.out
./a.out
aaa
bbb
cc

answered Apr 18 '15 at 07:35

leetom

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1
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score 0 · Answer 3 · edited May 23 '17 at 11:57

You need to read piped input from the standard input stream with cin as shown in this answer. Your file would become:

#include <iostream>
#include <string>

int main( int args, char ** argv )
{

    std::string lineInput;
    while (std::cin >> lineInput) {
        std::cout << lineInput << std::endl;
    }

}

Then your approach will work directly:

$ cat data | ./file
abc
def
ghi
jkl
mno
pqr
stu
vwx
yz

Difficulty in passing command line arguments

3 Answers3