shell scripting topic

[mitu]

@hiulit Add a -h option and display the help when this option is passed to the script.

[hiulit]

@mitu I'm sorry, I didn't explain myself clearly enough.

I already have a -h option that shows all the options available. What I meant is, how should I tell the user that the option --create-fun-fact can have:

• no options
• 1 option [system]
• 2 options [system rom]

That's what I've come up with: --create-fun-fact [] [system] [system rom]
Is that correct?

Did I explain myself better this time? :P

[mitu]

@hiulit said in shell scripting topic:

--create-fun-fact [] [system] [system rom]

Ah, ok. I think the correct syntax would be

--create-fun-fact [SYSTEM] [ROM]

Usually an argument in brackets ([arg]) means the argument is optional.

[hiulit]

@mitu I see! And if an argument is NOT optional? I have some of those around :P

[mitu]

@hiulit If it's not optional, just remove the brackets.

--create-fun-fact system [rom]

[meleu]

@hiulit can you explain the use case and provide some examples?

I'm sure we can find ways to make an option have zero, one or two options, but from a user point of view I think it's a bit confusing.

EDIT:
I can't see what would be the use for --create-fun-fact system rom, but if it's intended to be used on RetroPie, you can detect the system by looking the directory where the rom is located.

[hiulit]

@meleu I'll try to explain myself even better than the last time :P Here we go!

This all comes from the fun-facts-splashscreens-runcommand-onend.sh that has these lines:

SYSTEM="$1"
ROM_PATH="$3"
sudo "$SCRIPT_DIR/fun-facts-splashscreens.sh" --create-fun-fact "$SYSTEM" "ROM_PATH"

This is what creates the launching images when stoping the game. This is something the user doesn't need to care about. But then I already had --create-fun-fact in the help message so I wanted to let the user use it, like this:

• --create-fun-fact with no options passed creates a boot splashscreen.
• --create-fun-fact [SYSTEM] (SYSTEM can be all or any RetroPie system) creates launching images for all the systems, or the given system with the system's logo (and console if it exists).
• --create-fun-fact [SYSTEM] [ROM] (ROM can be an absolute path or just the ROM's name + ext, and then it takes the given system to look for the path) creates a launching image for the game.

Examples:

• --create-fun-fact
• --create-fun-fact all
• --create-fun-fact megadrive
• --create-fun-fact megadrive "/home/RetroPie/megadrive/Sonic the Hedgehog.zip"
• --create-fun-fact megadrive "Sonic the Hedgehog.zip"

I can see that from the user's perspective it could be a little confusing... Maybe it's better to split --create-fun-fact into two separate functions --create-fun-fact-boot-splashscreen and --create-fun-fact-launching-images.

Maybe I should remove this option from the help message? Just have it for myself to test?
That's something that can be done via the GUI, btw:

[meleu]

@hiulit You wouldn't want to create a launching image for Sonic using a NES splashscreen, would you? Well, my suggestion below does not have this kind of flexibility, but here it go:

help message

--create-fun-fact [system|path/to/a/ROM]     no arguments = create boot splashscreen
                                             system = create a launching image for system
                                             ROM = create a launching image for a ROM

If you wanna use this approach, please write a better help message for this option! ;)

code

#!/bin/bash

user="$SUDO_USER"
[[ -z "$user" ]] && user="$(id -un)"
home="$(eval echo ~$user)"

readonly RP_DIR="$home/RetroPie"
readonly RP_ROMS_DIR="$RP_DIR/roms"
readonly RP_CONFIG_DIR="/opt/retropie/configs"

function get_options() {

    case "$1" in

#H --create-fun-fact [system|path/to/a/ROM]     no arguments = create boot splashscreen
#H                                              system = create a launching image for system
#H                                              ROM = create a launching image for a ROM
        --create-fun-fact)
            if [[ -z "$2" ]]; then
                # NOTE: for this usecase the --create-fun-fact MUST be the
                #       last parameter used in the command line.
                echo "Let's create a boot splashscreen with a fun fact!"

            elif [[ -f "$2" ]]; then
                # NOTE: if it's a regular file, let's check if it's a ROM and
                #       create a splashscreen for this game.
                local rom_full_path="$(realpath "$2")"

                if [[ "$rom_full_path" != "$RP_ROMS_DIR"* ]]; then
                    echo "ERROR: \"$2\" is not on a valid ROM directory" >&2
                    exit 1
                fi

                # Reference for the tricks used to get the system's name below:
                # http://www.tldp.org/LDP/abs/html/parameter-substitution.html#PSOREX2
                system="${rom_full_path#$RP_ROMS_DIR/}"
                system="${system%/*}"

                echo "Let's create a launching image for \"$2\" using the ${system}'s one!"

            elif [[ -d "$RP_CONFIG_DIR/$2" ]]; then
                echo "Let's create a launching image for \"$2\" system!"

            else
                echo "ERROR: \"$2\": invalid argument." >&2
                exit 1
            fi
            ;;

#H --help                                       Print the help message and exit.
        --help|-h)
            sed '/^#H /!d; s/^#H //' "$0"
            echo
            exit 0
            ;;
    esac
}

get_options "$@"

testing

$ ./cff.sh --create-fun-fact
Let's create a boot splashscreen with a fun fact!

$ ./cff.sh --create-fun-fact abcd
ERROR: "abcd": invalid argument.

$ ./cff.sh --create-fun-fact nes
Let's create a launching image for "nes" system!

$ ./cff.sh --create-fun-fact ~/RetroPie/roms/nes
ERROR: "/home/meleu/RetroPie/roms/nes": invalid argument.

$ ./cff.sh --create-fun-fact ~/RetroPie/roms/nes/Contra\ \(USA\).zip 
Let's create a launching image for "/home/meleu/RetroPie/roms/nes/Contra (USA).zip" using the nes's one!

[hiulit]

@meleu Thanks for your reply! And no, I wouldn't want that

launching image for Sonic using a NES splashscreen
But my script prevents from doing that.

I'll try to paste every piece of code that I have, because it's very similar to what you have:

-cff|--create-fun-fact)
    is_fun_facts_empty
    if [[ -z "$2" ]]; then
        create_fun_fact
    else
        shift
        create_fun_fact "$@"
        shift
    fi
    ;;

If no arguments are passed called create_fun_fact without arguments, if there are any arguments, pass them all.

function create_fun_fact() {
    if [[ -z "$1" ]]; then
        create_fun_fact_boot
    else
        create_fun_fact_launching "$@"
    fi
}

There's more things going one here, but it basically calls one function or another depending on if there are arguments.
create_fun_fact_boot is self explanatory.
create_funfact_launching takes all the arguments and then:

function create_fun_fact_launching() {
    local system="$1"
    local rom_path="$2"

    if [[ "$system" == "all" ]]; then
        // Loop all systems and call create_fun_fact_launching "$system"
    else
        if [[ -n "$rom_path" ]]; then
            // Check if $system it's the same in "rom_path"
            if true
                // Create launching image for the game
            else
                // Create launching image for the system
        else
            // Create launching image for the system
        fi
    fi
}

More or less that what I do. I think it's similar of what you wrote.

But then again, I think maybe it's better to to have 2 separate options:

• --create-fun-facts-boot-splashscreen(doesn't accept any argument)
• --create-fun-facts-launching-images (accepts system and rom)

EDIT:
You can take a look for youself https://github.com/hiulit/RetroPie-Fun-Facts-Splashscreens/blob/new-gui-menu/fun-facts-splashscreens.sh ;)

[meleu]

I've just found this and decided to share here:

Pure Bash Bible

The goal of this book is to document known and unknown methods of doing various tasks using only built-in bash features. Using the snippets from this bible can help remove unneeded dependencies from scripts and in most cases make them faster.

[cyperghost]

@meleu Wow this is really helpfull ;) Cool snippets for bash coders. Thank you so much.

For ex:
Reverse array I did

for ((z=${#array[*]}-1; z>-1; z--)); do
       echo "${array[z]}"
done

Reverse array with the bash-bible

## Reverse an array

# ```sh
reverse_array() {
    # Usage: reverse_array "array"
    shopt -s extdebug
    f()(printf '%s\n' "${BASH_ARGV[@]}"); f "$@"
    shopt -u extdebug
}
# ```

Up to now my version seems a bit less complex. Maybe it's due my limited coding skills. I'm still learning ....

[cyperghost]

@meleu I think that's just a note to me ... BashPitfalls

function1(){
    local status=$(false)
    echo $?
}

Will return 0 which is obviously wrong
So the return code 0 just indicates the correct setting of a local setted value, which was correctly done ;)

So to get out of this make following

function1(){
    local status
    status=$(false)
    echo $?
}

This will put out correct value for "error" 1

[meleu]

@cyperghost yeah, that's a thing to be careful. I learned it while reading the RetroPie's Shell Style Guide: https://retropie.org.uk/docs/Shell-Style-Guide/#use-local-variables

[meleu]

I would like to share a little trick I learned today and also ask for some help...

First the short story

I was needing to check if the current hour is after 18h, then I tried this:

hour=$(date +%H)
if [[ $hour -gt 18 ]]; then
    echo "do something..."
fi

And then I got this error (please, forgive the non-english):

-bash: [[: 08: valor muito grande para esta base de numeração (token de erro é "08")

As you can see, the problem is that date +%H returns 08, and when I try to compare it, bash doesn't see 08 as a decimal number.

The solution is obviously getting rid of that leading zero. I decided that using sed would be overkill for such a simple task, then I've found a pure bash solution using a feature of $(( )).

hour=$(date +%H)
hour=$(( 10#$hour ))  # could also be an oneliner: $(( 10#$(date +%H) ))
if [[ $hour -gt 18 ]]; then
    echo "do something..."
fi

And now my script is working perfectly!

Now the help I mentioned earlier on the beginning of this post...

On that stackoverflow answer I see this:

The $(( )) sets up an arithmetic context and the 10# converts the number from base 10 to base 10 causing any leading zeros to be dropped.

Alright, but I like to see stuff on the official documentation in a hope to learn more tricks. The $(( )) is a bash builtin feature, but in the official documentation there's no mention to the 10# operand.

Any thoughts on where to get info about it?

[Sano]

@meleu That I can answer !
Actually it's in the very doc you mention :
https://www.gnu.org/software/bash/manual/bash.html#Shell-Arithmetic

Constants with a leading 0 are interpreted as octal numbers. A leading ‘0x’ or ‘0X’ denotes hexadecimal. Otherwise, numbers take the form [base#]n, where the optional base is a decimal number between 2 and 64 representing the arithmetic base, and n is a number in that base. If base# is omitted, then base 10 is used. When specifying n, the digits greater than 9 are represented by the lowercase letters, the uppercase letters, ‘@’, and ‘_’, in that order. If base is less than or equal to 36, lowercase and uppercase letters may be used interchangeably to represent numbers between 10 and 35.

[meleu]

@sano whoops! Didn't catch those little words 😅

Thanks Sano-san. And yeah, I learned more tricks!

[Sano]

@meleu Just FYI, you could just have used date +%-H ;)
Glad to see you here again BTW !

[meleu]

@sano ouch! Looks like I need RTFM some more...

From the date man page:

       By default, date  pads  numeric  fields  with  zeroes.   The  following
       optional flags may follow '%':

       -      (hyphen) do not pad the field

Thanks again, Sanso-sensei!

[Sano]

@meleu I really deserve no special credit for this, I just remembered something like this existed, probably had to use it in the past, too :)

[cyperghost]

A common mistake is often made by using grep.
It is often told that grep finds a total of all search strings within a text file due the -c switch. That is total nonsense .... -c just counts lines

So we miss

hello hello hello hello
hello

grep -c hello
2

We use a small hack ;)
Better is to use the -o option is will show occourences of search string listed in newline and now we pipe to wc -l ... and count lines again - now we catched them all ;)

hello hello hello hello
hello

grep -o hello | wc -l
5