docker_wrapper.sh

#!/bin/bash

wrapper() {
    ## Run a native command if it's available, otherwise from a docker image
    ## (Note: this only works with programs that read/write to stdin/stdout.
    ## Reading and writing files on the client host system is not supported.)
    DOCKER=${DOCKER:-docker}
    command=$1; shift
    WRAPPER_IMAGE=localhost/wrapper_${command}
    if which ${command} >/dev/null 2>&1; then
        ## Runs the native command passing args and stdin, prefixed with
        ## "command" to ignore the function with the same name:
        command ${command} "${@}" </dev/stdin
    else
        ${DOCKER} run --rm -i ${WRAPPER_IMAGE} ${command} "${@}" </dev/stdin
    fi
}

wrapper_build() {
    DOCKER=${DOCKER:-docker}
    dockerfile=$(</dev/stdin)
    command=$1; shift
    WRAPPER_IMAGE=localhost/wrapper_${command}
    if ! which ${command} >/dev/null 2>&1; then
        echo "${dockerfile}" | ${DOCKER} build -t ${WRAPPER_IMAGE} - 2>&1 >/dev/null
    fi
}


### USAGE:
# source wrapper.sh
# jq() {
#     wrapper_build jq <<EOF
# FROM alpine
# RUN apk add -U jq
# EOF
#     wrapper jq "${@}" </dev/stdin
# }
#
# ## Then use jq like normal, whether its installed or not:
# cat passwords.json | jq

zz_usage.txt

## OK, so I have some json to parse:
[ryan@maldek ~]$ JSON='{"username":"ryan", "password":"foo"}'

## But, I don't have jq installed:
[ryan@maldek ~]$ jq --version
bash: jq: command not found

## No problem, if I have docker/podman, I can import the wrapper functions
## and then define this function for jq:
[ryan@maldek ~]$ source docker_wrapper.sh
[ryan@maldek ~]$ 
jq() {
    wrapper_build jq <<EOF
FROM alpine
RUN apk add -U jq
EOF
    wrapper jq "${@}" </dev/stdin
}

## Now I have jq available, even though its not installed locally:
## This is the version that is in the docker container:
[ryan@maldek ~]$ jq --version
jq-master-v3.15.0_alpha20210804-4073-gb39e1241e8

## Now I can use jq to parse the json:
[ryan@maldek ~]$ echo ${JSON} | jq ".username"
"ryan"

## This version is a bit slow, since it builds and runs on my remote docker server.
## What if I install the native version of jq locally?
[ryan@maldek ~]$ sudo pacman -S jq
[sudo] password for ryan: 
resolving dependencies...
looking for conflicting packages...

Packages (1) jq-1.6-4

Total Installed Size:  0.67 MiB
...

## OK now I can still run jq the same way, but its running locally now:
## This is the version number for my system package of jq:
[ryan@maldek ~]$ jq --version
jq-1.6

## Still works (and its faster):
[ryan@maldek ~]$ echo ${JSON} | jq ".username"
"ryan"

## jq is a good use case for this since it operates only on stdin/stdout.
## For other programs that require reading/writing files, 
## this wouldn't work on a remote docker server, and so its not supported.