Detect if stdin is via keyboard or via < file?

[srbstar]

Can a program detect if it's stdin is
coming from keyboard input vs. being
redirected from a file?

If it's from a file, I want to fputs()
the text. But if it's from the keyboard,
I won't (don't want it typed, then
fputs()'d.

SRB

 

[Lew Pitcher]

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Can a program detect if it's stdin is
coming from keyboard input vs. being
redirected from a file?

Not in standard C, it can't.

But, with a platform-specific extension, it often can.

If it's from a file, I want to fputs()
the text. But if it's from the keyboard,
I won't (don't want it typed, then
fputs()'d.

You'll either have to resort to some sort of signal data (like a command
argument), or use a platform-specific extension to determine whether stdin
comes from a file or an interactive device.


- --
Lew Pitcher

Master Codewright & JOAT-in-training | GPG public key available on request
Registered Linux User #112576 (http://counter.li.org/)
Slackware - Because I know what I'm doing.
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[CBFalconer]

Not in standard C, it can't.

But, with a platform-specific extension, it often can.


You'll either have to resort to some sort of signal data (like a
command argument), or use a platform-specific extension to
determine whether stdin comes from a file or an interactive device.

However, on most unixlike systems there are methods available,
which are OT here. The OP can examine one such in my id2id-20,
which is available at:

<http://cbfalconer.home.att.net/download/id2id-20.zip>

 

[Chris Dollin]

Can a program detect if it's stdin is
coming from keyboard input vs. being
redirected from a file?

If it's from a file, I want to fputs()
the text. But if it's from the keyboard,
I won't (don't want it typed, then
fputs()'d.

I found the most straightforward tactic in a similar situation
(whether to issue a prompt or not, for an interactive interpreter)
to be a command-line flag. The program no longer needs to be able
to answer the question.