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My problem is, I want a script which reads content from a pipe, checks if it's empty and output it if not, as seen here:

#!/bin/bash
var=$(cat -)
if [ -n "$var" ]
then
    echo "$var"
else
    echo "Pipe was empty"
fi

The problem is, cat reads from stdin, if the pipe is empty. Is there any way to prevent cat from doing that? Or is cat the wrong tool to use here?

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1 Answer

up vote 2 down vote accepted

Use read -t 0 -N 0 to detect if data is available on stdin. Use test -t 0 or tty to try to detect if a pipe is connected to stdin.

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I believe -t 0 and -N 0 are redundant. –  Hello71 Apr 27 '11 at 2:21
    
Any way to put that together in a script, because I'm not sure how to realize that. Sorry, but I don't use read very often (only read -n or read as is) –  MechMK1 Apr 27 '11 at 4:31
    
if test -t 0; then echo "None"; else echo "$(cat -)"; fi Just figured out by trial and error –  MechMK1 Apr 27 '11 at 4:34
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