[SOLVED] Bash fail use file descriptor assigned a file that resides in /tmp

zeroone · 07-13-2023, 06:26 PM

Does one experienced too that
Bash cannot use file descriptor assigned a file that resides in /tmp ?
i.e. inside script:

Code:

...
exec 3< <(/tmp/dls1)

while read -r -u3 f1; read -r f2
do
 # ...
done < <(cat /tmp/dls2)
...

output:
...

bash: /tmp/dls1: Permission denied

While the second file is read into f2 works. Please advise the wisest solution

michaelk · 07-13-2023, 07:25 PM

Code:

exec 3< <(/tmp/dls1)

I have not tested your code but using process substitution for the redirect is probably the cause of your script not working. Instead try the following:

Code:

#!/bin/bash

while read -r f1 && read -r -u 3 f2
do
   echo "$f1 $f2"
done <"/tmp/dls1" 3<"/tmp/dls2"

I assume your user has read permissions for both files?

NevemTeve · 07-13-2023, 11:30 PM

@OP Are these synonyms or not? If not, what is the difference?

Code:

exec 3</tmp/dls1
exec 3< <(/tmp/dls1)

pan64 · 07-14-2023, 01:01 AM

Quote:

Originally Posted by zeroone

Bash cannot use file descriptor assigned a file that resides in /tmp ?

this is a definitely incorrect conclusion.

It can be a real permission issue (permission is really denied), but I think you missed the cat in the first line.

Code:

exec 3< <(cat /tmp/dls1)

But cat is not required at all (see uuoc), the previous suggestions are much better.

Additionally would be better to use shellcheck to catch errors like this.

michaelk · 07-14-2023, 04:17 AM

Quote:

Originally Posted by NevemTeve

@OP Are these synonyms or not? If not, what is the difference?

Code:

exec 3</tmp/dls1
exec 3< <(/tmp/dls1)

No, the first is a redirect and the second is process substitution. It isn't technically a syntax error so shellcheck will not report an error. I believe it fails because /tmp/dls1 isn't an executable and that as posted you are missing the cat command. Using process substitution is not required as I posted above.

zeroone · 07-15-2023, 01:36 AM

Quote:

Originally Posted by NevemTeve

@OP Are these synonyms or not? If not, what is the difference?

Code:

exec 3</tmp/dls1
exec 3< <(/tmp/dls1)

Solved by solution of your

Code:

exec 3</tmp/dls1

its synonym to corrected 2nd one: exec 3< <(cat /tmp/dls1)

MadeInGermany · 07-16-2023, 05:48 AM

Not a synonym,
but much more complex, and yes, with the same result.

Further, a lasting open with exec (until there is a close with another exec) is more complicated than redirecting a code block a la post#2
The loop is a code block; when redirected then the open occurs when the code block starts, and the close occurs when the code block ends.
BTW a { } forms a custom code block:

Code:

{
read line1
read line2
} </etc/group