CODEWITHSUNDEEP
cshelliostdin
sean_xia
sean_xia

Reputation: 173

Writing a shell using C. How to differentiate interactive mode and batch mode

I am writing a shell with both interactive and batch modes in C. I would like to print the prompt in interactive mode and don't show it in batch mode.

i.e.

bash> ./myshell

should show prompt, and

bash> ./myshell < sample.txt

should only show the output from the commands in "sample.txt", but not the prompts.

Since the parent process (which is bash) made the stdin redirection, I am not sure how can myshell tell if the input stream was from stdin or from a file?

Thanks very much in advance for the help.

Upvotes: 3

Views: 1878

Answers (1)

Jonathon Reinhart
Jonathon Reinhart

Reputation: 137438

isatty(3) can be used to determine if a given file descriptor is a tty. Shells will use this to determine what kind of input to expect.

For example:

if (isatty(STDIN_FILENO)) {
    // Interactive shell
}
else {
    // Redirected stdin
}

Upvotes: 4

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