bac acts as a Unix command-line interface wrapper around the Avalanche JSON API, making it easier to call simple methods.

-f formats the output using jq.
-n does nothing but display the Curl command.
-h gives help.
Arguments are key:value pairs (quotes unnecessary), pairs being separated by spaces.
Endpoint is inferred from the service part of the method.

bac -f avm.getBalance address:X-avax1tmnpf87ph0pap4p507zfr0zesafnj5qh0sdkjc assetID:AVAX

Providing an incomplete method name (i.e. without . or _) has it grepped in [/usr/local/etc/]bac.sigs and matching method signatures are displayed. The file has been generated by scraping the documentation pages, some basic text processing, and manual editing. Methods suffixed with ! are deprecated. Arguments suffixed with ° are optional. Example:

$ bac blockchain
platform.createBlockchain! : subnetID, vmID, name, genesisData, encoding°, from[]°, changeAddr°, username, password
platform.getBlockchains!
platform.getBlockchainStatus : blockchainID

Ok, this is the Basic Avalanche CLI, but you can do whatever you want, even with the avax API now (beta). You can also use avalanche-cli. You may find it better suited for complex requests.

You write objects pretty much as you would in JSON, only simpler:

key1:{key2a:value2a key2b:{key3a:value3a key3b:value3b}}

Same for arrays:

key1:[value1a value1b]

The script works in any directory by calling ./bac … provided it has execution rights (chmod 755 bac if it's not the case), but you can install it system-wide:

sudo install -m 755 bac /usr/local/bin
sudo install -m 644 bac.sigs /usr/local/etc

There are no prerequisites if you only need raw outputs. The -f (format) option wants jq, which you can install using apt install jq.

All services are (supposed to be) supported, except

• the C-chain (not fully tested, some methods do work)
• there's always one more bug (Lubarsky's Law of Cybernetic Entomology)

… for now.

gensigs.pl never really worked and has been discarded.
The -n option forgets the simple quotes.
The EVM API seems incomplete.
The avax RPC endpoints are unmanageable in an automatic way: see https://docs.avax.network/apis/avalanchego/apis/c-chain.
You shouldn't try to understand the PARAMS sed regexps, unless you're into Malbolge.
Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems. (J. Zawinski)