Sending inputs to C program and printing them - c

Question

Trying to write a script that takes a file of inputs and sending them one-by-one to a C program whenever the program asks for input (scanf).
I want my script to print every input before it sends it to the program.
The whole output of the C program (including the inputs I provided) should be print to a file.
Looking for a solution without changing my C code.
For ex:
My C Program: test.c
#include <stdio.h>
int main()
{
char a[50];
int b;
printf("Enter your name:\n");
scanf("%s",a);
printf("HELLO: %s\n\n", a);
printf("Enter your age:\n");
scanf("%d",&b);
printf("Your age is: %d\n\n", b);
return 0;
}
My Script: myscript.sh
#!/bin/bash
gcc test.c -o mytest
cat input | ./mytest >> outputfile
I also tried
#!/bin/bash
gcc test.c -o mytest
./mytest < input > outputfile
My Input File: input
Itzik
25
My Output File: outputfile
Enter your name:
HELLO: Itzik
Enter your age:
Your age is: 25
Desired outPutFile:
Enter your name:
Itzik
HELLO: Itzik
Enter your age:
25
Your age is: 25
Thanks a lot!

Answer 1

Oh my .. this is going to be a bit ugly.
You can start the program in the background, with it reading from a pipe, then hijack that pipe and write to it, but only when the program is waiting for input. And before you write to the pipe, you write to standard output.
# Launch program in background
#
# The tail command hangs forever and does not produce output, thus
# prog will wait.
tail -f /dev/null | ./prog &
# Capture the PIDs of the two processes
PROGPID=$!
TAILPID=$(jobs -p %+)
# Hijack the write end of the pipe (standard out of the tail command).
# Afterwards, the tail command can be killed.
exec 3>/proc/$TAILPID/fd/1
kill $TAILPID
# Now read line by line from our own standard input
while IFS= read -r line
do
# Check the state of prog ... we wait while it is Running. More
# complex programs than prog might enter other states which you
# need to take care of!
state=$(ps --no-headers -wwo stat -p $PROGPID)
while [[ "x$state" == xR* ]]
do
sleep 0.01
state=$(ps --no-headers -wwo stat -p $PROGPID)
done
# Now prog is waiting for input. Display our line, and then send
# it to prog.
echo $line
echo $line >&3
done
# Close the pipe
exec 3>&-
I've compiled your source code above to an executable named prog and saved above code into pibs.sh. The result:
$ bash pibs.sh < input
Enter your name:
Daniel
HELLO: Daniel
Enter your age:
29
Your age is: 29

Answer 2

What you are asking is really not possible without writing a program that parses the output from test.c and knows what is a prompt for input, and what is not.
Depending on how complicated your program is, you may have some luck with the chat program (see man chat) or GNU expect.
Your best bet is, as "BobRun" says, to modify your program. No matter how much you don't want to modify your program, it is time to put all those scanf() you might have littered through you code, behind proper input functions like this:
int input_int(const char *prompt)
{
printf ("%s:\n", prompt)
int i = 0;
scanf("%d", &i);
/* Eat rest of line */
int ch;
do
ch = fgetc(stdin);
while (ch != '\n' && ch != EOF)
return i;
}
Now, adding error checking and echoing of input becomes trivial. And your program might become easier to read
Getting rid of that bug/security-hole to happen scanf("%s", ...) would also become easy.
And if you think this is a large job, well suck it up. You should really have done it from the beginning when the job was small. And if you delay the job any more, it will soon be humungus.