How to redirect standard input and output with Bash

Question

#!/bin/bash
./program < input.txt > output.txt

The > output.txt part is being ignored so output.txt ends up being empty.

This works for the sort command so I expected to also work for other programs.

Any reason this doesn't work? How should I achieve this?

Perhaps the output from ./program is going to the standard error? Try 2> output.txt — Richante
– Richante, Commented Apr 9, 2012 at 16:59
@Richante LOL that's odd but now works (why do you write the answer in a comment?) thanks — Inuart
– Inuart, Commented Apr 9, 2012 at 17:08

Oliver Charlesworth · Accepted Answer · 2012-04-09 17:01:32Z

15

The most likely explanation is that the output you're seeing is from stderr, not stdout. To redirect both of them to a file, do this:

./program < input.txt > output.txt 2>&1

or

./program < input.txt &> output.txt

answered Apr 9, 2012 at 17:01

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1 Comment

How would you do something like ./program < input.txt | program2 | program n > output.txt ?