Mechanism for returning a string from C main() program

I know that C program generally ends with return, whe开发者_开发技巧re we return the status of the program. However, I want to return a string. The reason is that, I will be calling the C-executable from a shell script and printing the returned string. Is there any mechanism for the same ?

There is no such mechanism; the return code is expected to be a byte. If you want to output a string from your program then use something like printf() and command substitution in the shell script to capture it.

You cannot.

The best thing you could do is writing the string somewhere (on standard output, standard error or some file); then the shellscript will get your string from there.

Standard output (thus using just a printf) is probably the best solution, since it will be very easy from your C program print the string, and very easy for the shellscript getting that data:

From shell script:

STRING="$( ./your_program argv1 argv2 )"

There is not way to return a string from main(). Maybe the program itself should print the string ?

Just output the string you want to return to standard output with printf. Then in your script, do something like this:

SOMESTRING="`./yourprogram`"

The backticks will capture the output of the program, which will be the string you printed.

You can't, but you don't need to either. You return a stat code from main, but you can always re-direct the output and capture it in your shell script.

You cannot - you can only return an integer.

Remember that C was developed alongside Unix. Unix programs return an integer value which is intended as a status code. If a program was to return string(s) it would write them to stdout, and then the user (or a script) would pipe it into something useful.

MS DOS also had number-only status values.

You have to print the string to stdout and use the shell's command substitution to read the result:

"`command`"

or:

"$(command)"

Either way, you should use the enclosing double-quotes as above. Note that this method has a potentially-serious problem that it removes all training newlines from the command's output. If you need to preserve the exact output, try:

output="$(command ; echo x)"
output="${output%x}"

Since OP mentioned that this is for a password, another piece of advice: once you've read a password into a shell variable, never pass it on the command line to other programs. Command lines are usually world-readable. Instead of something like

wget "http://$user:$pass@host/foo"

try something like

wget -i - << EOF
http://$user:$pass@host/foo
EOF

Here-files as in this example are useful with a number of programs which need to take passwords from scripts.