vbl

Installation

Several ways to install the library

General information

In general, the installation process looks as follows:

  1. Download the latest, stable, or a version of a module from the library.

    The URL of a module's file should be constructed of three parts:

    • The base URL. It is http://vbl.vorakl.com/ (https is also supported)
    • The version. A version can be latest/, stable/ or one of published versions (e.g. v2.0.3/)
    • The name of a module (e.g. sys)

    For example:

    • http://vbl.vorakl.com/latest/sys
    • http://vbl.vorakl.com/stable/exec
    • http://vbl.vorakl.com/v2.0.3/str

    In addition, each module comes with a sha256 hash (${module}.sha256). For example, these all are possible URLs of sha256 hashes:

    • http://vbl.vorakl.com/latest/exec.sha256
    • http://vbl.vorakl.com/v2.0.2/sys.sha256
  2. Include it into your script.

    Usually, external files with Bash code are included by source /path/to/file or . /path/to/file instuctions.

There are a few common ways to do these two steps.


Download a module at run-time using curl

This code downloads the latest version of the sys module and doesn't save it localy:

source <(curl -sSLf http://vbl.vorakl.com/latest/sys)

Download a module by curl and check an integrity by sha256sum

This snippet uses two external commands (curl and sha256sum) to download a module (a version can be also specified), checks its sha256 hash and keeps everything in memory, without saving a file on a disk. If everything is fine, then the module will be included. Otherwise, the script exits with an error message. To simplify things, it's represented as a separate function import_lib:

# usage: import_lib lib_name [version]
import_lib() {
    local _lib_name _ver _lib_content _lib_hash _origlib_hash

    _lib_name="${1?The lib name is empty}"
    [[ -n "$2" ]] && _ver="$2/" || _ver="latest/"
    _lib_content="$(curl -sSLf http://vbl.vorakl.com/${_ver}${_lib_name})"
    _lib_hash="$(set -- $(sha256sum <(echo "${_lib_content}") ); echo "$1")"
    _origlib_hash="$(set -- $(curl -sSLf http://vbl.vorakl.com/${_ver}${_lib_name}.sha256); echo "$1")"
    if [[ "${_lib_hash}" == "${_origlib_hash}" ]]; then
        source <(echo "${_lib_content}")
    else
        echo "The '${_ver}${_lib_name}' module hasn't been loaded" >&2
        exit 1
    fi
}

This is how it can be used in code:

#!/bin/bash

start() {
    import_lib sys
    # import_lib sys stable

    # add your code here
}

import_lib() {
    local _lib_name _ver _lib_content _lib_hash _origlib_hash

    _lib_name="${1?The lib name is empty}"
    [[ -n "$2" ]] && _ver="$2/" || _ver="latest/"
    _lib_content="$(curl -sSLf http://vbl.vorakl.com/${_ver}${_lib_name})"
    _lib_hash="$(set -- $(sha256sum <(echo "${_lib_content}") ); echo "$1")"
    _origlib_hash="$(set -- $(curl -sSLf http://vbl.vorakl.com/${_ver}${_lib_name}.sha256); echo "$1")"
    if [[ "${_lib_hash}" == "${_origlib_hash}" ]]; then
        source <(echo "${_lib_content}")
    else
        echo "The '${_ver}${_lib_name}' module hasn't been loaded" >&2
        exit 1
    fi
}

start "$@"

Download a module using a pure Bash without saving on a disk

This one is quite tricky. For downloading a module it doesn't use any external tools, such as curl or wget, just a pure Bash code. It also doesn't store a file on a disk:

lib_name="latest/sys"
source <(
    exec 3<>/dev/tcp/vbl.vorakl.com/80
    printf "GET /${lib_name} HTTP/1.1\nHost: vbl.vorakl.com\nConnection: close\n\n" >&3
    body=0;
    while IFS= read -u 3 -r str; do
        if (( body )); then
            printf "%s\n" "${str}"
        else
            [[ -z "${str%$'\r'}" ]] && body=1
        fi
    done
    exec 3>&-
)

or in a shorter form, as a one-liner:

lib_name="latest/sys"; source <(exec 3<>/dev/tcp/vbl.vorakl.com/80; printf "GET /${lib_name} HTTP/1.1\nHost: vbl.vorakl.com\nConnection: close\n\n" >&3; body=0; while IFS= read -u 3 -r str; do if (( body )); then printf "%s\n" "${str}"; else [[ -z "${str%$'\r'}" ]] && body=1; fi done; exec 3>&-)

This is the example of how the snippet can be used in code:

#!/bin/bash

start() {
    lib_name="latest/sys"
    source <(exec 3<>/dev/tcp/vbl.vorakl.com/80; printf "GET /${lib_name} HTTP/1.1\nHost: vbl.vorakl.com\nConnection: close\n\n" >&3; body=0; while IFS= read -u 3 -r str; do if (( body )); then printf "%s\n" "${str}"; else [[ -z "${str%$'\r'}" ]] && body=1; fi done; exec 3>&-)
}

start "$@"