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Re: How to test if stdin is empty, if not empty print to stdout, otherwi
From: |
Peng Yu |
Subject: |
Re: How to test if stdin is empty, if not empty print to stdout, otherwise do something else. |
Date: |
Wed, 25 Mar 2020 09:08:22 -0500 |
> The problem with this thread, as with all of Peng Yu's threads, is that
> nobody knows what the actual GOAL is. Peng Yu will never reveal the goal,
> either, no matter how many times you ask.
I have emailed you before. The goal does not matter.
> I can think of at least two possible goals which might drive someone to
> ask how to test whether stdin has input available.
Thanks for your suggestion. However, I only use stdin to take input
data whenever possible. And I don't want to add an additional switch
to tell the program whether the input contains data or not as it is
redundant to add such a switch when the information whether the input
is empty is contained in the input itself.
> (1) "I want to write a utility that can either take data as an argument,
> or read data from stdin. I want it to do the correct thing
> automatically, without having to pass a --stdin option or whatever."
>
> In this case, the test is simply reversed. Don't try to test whether
> stdin has input available. Test whether an argument was passed.
>
> thing() {
> if [[ $1 ]]; then
> stuff "$1"
> else
> local in
> in=$(cat; printf x)
> in=${in%x}
> # Or, in=$(cat) if you want to strip newlines. Or, read -r in if
> # you only want one line of input, with newline stripped.
> stuff "$in"
> fi
> }
>
> (2) "I'm writing an keyboard-event-driven user interface that should handle
> keyboard presses whenever they occur, but should not block to wait for
> them."
This is not relevant to my goal.
--
Regards,
Peng
- How to test if stdin is empty, if not empty print to stdout, otherwise do something else., Peng Yu, 2020/03/24
- Re: How to test if stdin is empty, if not empty print to stdout, otherwise do something else., Eli Schwartz, 2020/03/24
- Re: How to test if stdin is empty, if not empty print to stdout, otherwise do something else., Peng Yu, 2020/03/24
- Re: How to test if stdin is empty, if not empty print to stdout, otherwise do something else., João Eiras, 2020/03/24
- Re: How to test if stdin is empty, if not empty print to stdout, otherwise do something else., Koichi Murase, 2020/03/25
- Re: How to test if stdin is empty, if not empty print to stdout, otherwise do something else., Greg Wooledge, 2020/03/25
- Re: How to test if stdin is empty, if not empty print to stdout, otherwise do something else.,
Peng Yu <=
- Re: How to test if stdin is empty, if not empty print to stdout, otherwise do something else., Eli Schwartz, 2020/03/25
- Re: How to test if stdin is empty, if not empty print to stdout, otherwise do something else., Peng Yu, 2020/03/25