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Comment by grondilu | Hacker News Reader

> I’ve idealized the four steps as separate functions.

Does the author know he can write functions in bash?

I mean, if he wants to compare programming languages, he should at least compare similar programming styles.

Bash is great for OS scripts because it has built-in commands and syntax for dealing with processus and their inter-communication (pipes and stuff).

Python has NOTHING about that. If you want to do this, you have to use a module, read its documentation, and be prepared to write ugly, verbose method calls all around.

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The problem with Bash functions is that they aren't really functions -- more like subroutines. You can't even return a value from a Bash function (just a numeric status code).

Most of the functions the author wrote wouldn't even be possible in Bash, if only because they utilize return values. So your suggestion that he "compare similar programming styles" is practically impossible without using implicit state-passing methods in Bash, which are much more awkward and error-prone than real functions.

Having said that, I agree that writing scripts in Python adds a lot of overhead over Bash, and should only be done if you are implementing significant complicated logic more than just I/O. (For example, retries, exponential backoff, business logic, exception handling, etc.)

You can output data from a function and pipe it just like any other program, right? So that's how you tend to return values from bash functions.

> You can't even return a value from a Bash function (just a numeric status code).

You can print a textual result and store it in a variable, which is a pretty natural pattern in bash, e.g.,

    set -e
   
    download_command () {
        if type wget >/dev/null 2>&1; then
            echo "wget -q -O-"
        elif type curl >/dev/null 2>&1; then
            echo "curl -sL"
        else
            echo "Error: curl or wget is required" >&2
            exit 1
        fi
    }

    download=$(download_command)
    public_v4=$($download http://whatismyip.akamai.com/)
    public_v6=$($download http://ipv6.whatismyip.akamai.com/)

The numeric status code is best used to indicate errors (as above, with set -e), not to overload for data.

I do agree that I'd prefer being able to return actual structured data and not strings -- but honestly you can pass e.g. JSON back-and-forth between commands that take JSON, and into `python -c 'import sys, json; something(json.loads(sys.stdin))'` if you need it for a small part of a script that's generally better written in sh.

I roughed out a LISP interpreter in Bash. Since I just stored s-expressions in bash variables and/or returned s-expressions with echo and/or parsed the parens to compute cdr or car, it was not a big success.

Return-values in (ba)sh is text output. You can pipe to and from a function in bash, and you can use replacement [eg: host=$(hostname)].

It's different, but it's a powerful paradigm.

I don't understand your first statement. I thought that if you wrote your own function/routine/blah you can have it return anything you might like to handle - in one side and out the other.

{print_this_garbage_out=`do_a_little_dance` #maybe even with awk|sed|perl|python|sql|mom

retval_for_something_hopefully_cool=$? # or some other requisite test/set, limit sky

echo "${print_this_garbage_out}"

return ${retval_for_something_hopefully_cool}} # don't exit, because that might be silly

The bash is sort of like your machine code, it, like your machine, can use anything it has access to, if told properly. So I don't understand "can't even return a value". I don't know much about bash for bash's sake so I'm wondering if I may have missed something along the way.

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