Bash Script exec file descriptor returning "not found"

Question

I want to set all debugging output to a log file. So I checked command line - bash: set -x logs to file | Ask Ubuntu and followed the instructions.

test-script:

#!/bin/bash
exec 5 >/var/log/test.log
export BASH_XTRACEFD=5
main(){
set -x
echo hello
set +x
}
main

run:

./test-script

returns:

exec: 5: not found

The manual shows you can do this as well, so why is the above not working?

Answer 1

There should be no space between 5 and > on the exec line.

With the space, the script tries to execute a command called 5, which is why you get "not found".

Without the space, you attach file descriptor 5 to the given file name for output.

Additionally, there is no need to export the variable BASH_XTRACEFD, it's enough to just set it:

#!/bin/bash 

exec 5>test.log   

BASH_XTRACEFD=5

main () {           
    set -x        
    echo hello    
    set +x        
}

main 

Answer 2

The error gets you halfway there:

exec: 5: not found

exec tried to execute a command called 5, and didn't find it.

The syntax for redirecting a file descriptor calls for no space between the file descriptor number and the redirection operator, like so:

exec 5> /var/log/test.log