Get `top` output for non-interactive shell

In Linux, you can try this:

top -bn1 > output.txt

From man top:

-b : Batch-mode operation
            Starts top in 'Batch' mode, which could be useful for sending
            output from top to other programs or  to  a  file.   In  this
            mode, top will not accept input and runs until the iterations
            limit you've set with the '-n' command-line option  or  until
            killed.
....
-n : Number-of-iterations limit as:  -n number
            Specifies  the  maximum  number of iterations, or frames, top
            should produce before ending.

With OS X, try:

top -l 1

From top OSX manpage:

 -l <samples>
              Use logging mode and display <samples> samples, even if 
              standard output is a terminal. 0 is treated  as  infinity.   
              Rather than redisplaying, output is periodically printed in 
              raw form. Note that the first sample displayed will have an 
              invalid %CPU displayed for each process,  as it is calculated 
              using the delta between samples.

If it is an sh script - as in, it explicitly references #!/bin/sh - which might still be bash but would be like invoking it with --posix --no-rc --no-profile - then you can specify the ENV file with the ENV environment variable:

ENV=/path/to/rcfile sh

Specific variables need either to be declared on the command-line - as above for $ENV - or else with export. For example, for $PATH you do:

export "PATH=$PATH:/some/more/paths"; sh

The $BASH_ENV variable you reference is not a file you need to source - and it isn't interpreted anyway when bash is invoked as sh - but is rather a path to a file that is sourced when a non-interactive bash shell is invoked - such as with a script that specifies the:

#!/bin/bash

...or whatever bang line.

Another way you might like to invoke your script/shell is with the env utility. It can be used to explicitly remove values from the environment, or else, as is usually easiest, to wipe it clean from the start:

env - BASH_ENV=/path/to/rcfile /usr/bin/bash /some/script/file

That will tell env to invoke the /usr/bin/bash command - with all its arguments appended - with the $BASH_ENV environment variable specified, but otherwise with a clean environment entirely.