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brewi

#!/usr/bin/env rad
---
Facilitates checking a brew formula before installing it.
---
args:
    formula string # Name of the formula to install.
    cask c bool    # Enable if it's a cask.

$!`brew info {formula}`
if confirm():
    $!`brew install{cask ? " --cask" : ""} {formula}`

> brewi --help
Facilitates checking a brew formula before installing it.

Usage:
  brewi <formula> [cask]

Script args:
      --formula string   Name of the formula to install.
  -c, --cask             Enable if it's a cask.

Tutorial: Building brewi

Motivation

I tend to run brew info before installing formulas just to double-check that I've got the right one. Most of the time, it is, so I follow that with a brew install.

Rather than writing out these two commands manually each time, it'd be neat if I had an alias, which not only saved some characters, but did this workflow for me.

Writing the script

We can use rad to create the script file for us.

rad new brewi -s

This will set us up with an executable script named brewi, and the -s simplifies the template it's instantiated with to contain just a shebang.

The shebang will allow us to invoke the script as brewi from the CLI rather than writing out rad ./brewi. Open up brewi in your editor, and you should see something like this:

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#!/usr/bin/env rad

Let's begin editing it. First, we want to quickly describe what the script is aiming to do, so we'll add a file header.

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#!/usr/bin/env rad
---
Facilitates checking a brew formula before installing it.
---

We want the script to accept a formula as an argument, i.e. the formula we may be installing. It'll be a string, so let's add this in an arg block. We'll include a little comment to improve our usage string.

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#!/usr/bin/env rad
---
Facilitates checking a brew formula before installing it.
---
args:
    formula string # Name of the formula to install.

formula will serve both as the variable name for the rest of the script, and be exposed to the user as the script's CLI API.

Setup done. First thing we'll wanna do is run brew info with the formula. We'll do this via a shell command.

Specifically, we'll use a critical shell command, because if the command fails (including if the formula just doesn't exist), we want to just print the error and exit the script.

This uses the $! syntax.

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#!/usr/bin/env rad
---
Facilitates checking a brew formula before installing it.
---
args:
    formula string # Name of the formula to install.

$!`brew info {formula}`

We use string interpolation to insert the formula into the command.

You can try running the command now! Make sure it's executable (chmod +x ./brewi).

Next, we want to ask the user if they'd like to proceed with installing the formula. For that, RSL offers the confirm function. The default prompt is Confirm? [y/n] >, which works fine for us here, so we'll do a simple 0-arg confirm() call. The function returns a bool for yes/no, so we'll put it in an if statement.

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#!/usr/bin/env rad
---
Facilitates checking a brew formula before installing it.
---
args:
    formula string # Name of the formula to install.

$!`brew info {formula}`
if confirm():
    $!`brew install {formula}`

Feel free to try it again now!

One last touch: we should also allow installing casks with this script. We'll aim to offer a simple -c flag users can set which modifies the command.

We'll add the bool arg, and insert an additional interpolation in our brew install command, leveraging RSL's ternary syntax. We need to pay close attention to whitespace so we make sure the command comes out correct in the cask and non-cask cases.

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#!/usr/bin/env rad
---
Facilitates checking a brew formula before installing it.
---
args:
    formula string # Name of the formula to install.
    cask c bool    # Enable if it's a cask.

$!`brew info {formula}`
if confirm():
    $!`brew install{cask ? " --cask" : ""} {formula}`

Note the shorthand flag in cask c bool.

Done! If you'd like to see a more complex example next, check out hm.