[SOLVED] bash: [ -t 0 ] does return false if script is piped into bash on the console

framp · 10-02-2022, 01:11 PM

I want to pipe a script into bash from the console like

Code:

cat t.sh | bash -s -- -1

This works fine but for some reasons

Quote:

[ -t 0 ]

returns false even the command is invoked from the console.

I wrote a small script to demonstrate the effect:

Quote:

#!/bin/bash

n=${1:-1}

if [ -t 0 ]; then
echo "$n: Interactive"
else
echo "$n: Non interactive"
fi

if (( $n <= 1 )); then
./t.sh $(($n+1))
fi

If I invoke the script on the console with

Quote:

./t.sh 0

I get

Quote:

./t.sh -1
-1: Interactive
0: Interactive
1: Interactive
2: Interactive

If I use

Code:

cat ./t.sh | bash -s -- -1
-1: Non interactive
0: Non interactive
1: Non interactive
2: Non interactive

Any idea why this doesn't work?

wpeckham · 10-02-2022, 01:55 PM

Because bash is running within a pipe subshell, not directly at your terminal. Bash is acting, in other words, exactly as the man page specifies.

So it IS working, your understanding is just lacking.

I hope this helps AND gives you a clue as to where to find out more.

computersavvy · 10-02-2022, 01:59 PM

A slight change to your script

Code:

#!/bin/bash

#n=${1:-1}
n=$1

if [ $n -eq 0 ]; then
echo "$n: Interactive"
else
echo "$n: Non interactive"
fi

if (( $n <= 1 )); then
./t.sh $(($n+1))
fi

yields

Code:

$ ./t.sh -1
-1: Non interactive
0: Interactive
1: Non interactive
2: Non interactive

You can research the topic at https://tldp.org/LDP/abs/html/index.html to understand why this change works.

framp · 10-02-2022, 02:31 PM

Quote:

Originally Posted by wpeckham

I hope this helps AND gives you a clue as to where to find out more.

I see. I thought the interactive property is inherited by subshells. But frankly I have no clue where to search and which keyword to use to find a solution for my issue.

Quote:

Originally Posted by computersavvy

Nice code change. But this doesn't help me at all :-(

I just found my post where I explained my reason why I use this way to call a bash script. https://www.linuxquestions.org/quest...1/#post6172880

Unfortunately I now need a way to pass the interactive property down to the called script.

MadeInGermany · 10-02-2022, 07:51 PM

The pipe hides the original input.
Also there is useless use of cat.
The following solves both:

Code:

< t.sh bash -s -- -1

MadeInGermany · 10-03-2022, 01:06 AM

Now I had a look at your previous post.
If you must feed it by a program (curl, not cat) then try to run the shell in the foreground (and the program in the background).

Code:

sudo bash -s -- -o < <( curl ... )

Another attempt is the "lastpipe" shell option:

Code:

shopt -s lastpipe
curl ... | sudo bash -s -- -o

pan64 · 10-03-2022, 01:07 AM

Quote:

Originally Posted by framp

I see. I thought the interactive property is inherited by subshells. But frankly I have no clue where to search and which keyword to use to find a solution for my issue.

No, that is not possible. Every invocation of bash can (and will) decide if it was started in interactive mode - by itself. Interactive mode also assumes there is a real input (keyboard) attached to that bash.
Subshells and other scripts which are just executed are not interactive shells, and that is the intended way (especially when the input and output are connected to pipes)

Quote:

Originally Posted by framp

Unfortunately I now need a way to pass the interactive property down to the called script.

You must not do that. You need to redesign your script. As it was suggested by MadeInGermany you can avoid starting a subshell, but in some cases it does not help (obviously it depends on your script).

framp · 10-03-2022, 04:17 AM

Quote:

Originally Posted by MadeInGermany

The pipe hides the original input.
Also there is useless use of cat.
The following solves both:

Code:

< t.sh bash -s -- -1

Thank you very much for your answers. They are very interesting. Now I have something to test and to work with :-)

As far as I can see right now I have to redesign the code (suggested by @pan64) and solve the issue with an invocation parameter to signal the script is running in interactive mode (that's what I think @comutersavvy suggested with his code change - sorry I didn't catch this yesterday) because I detected the called script also uses

Code:

BASH_SOURCE[0]

to extract the directoryname of the script but this is empty if the script is piped into bash. Or I have to find a way to remove the usage of

Code:

BASH_SOURCE[0]

.

Thank you very much to everybody for your help. I now know which alternatives I have and will choose one of them :-)

pan64 · 10-03-2022, 07:13 AM

you may try to use $0 instead of BASH_SOURCE[0], probably that will work. And would be nice to show us a better example about that issue.

framp · 10-03-2022, 01:44 PM

Quote:

Originally Posted by pan64

you may try to use $0 instead of BASH_SOURCE[0], probably that will work. And would be nice to show us a better example about that issue.

I try to find a solution and will post it here. If I don't find a solution I will write code which explains my issue.

framp · 10-05-2022, 01:42 PM

I detected other issues which are related to the way the called script works with stdin, stdout and stderr :-(. Therefore I decided to split everything into two commands: One which downloads the script and the other which calls the downloaded script with sudo.

Again: Thank you very much for your comments and help.