ShellB

ShellB (pronounced Shelby) is a shell script builder. The goal is to be a (near) drop-in replacement for Ruby's Shell class

I've long loved Ruby's Shell class, essentially a DSL for building a shell script.

Imagine my dismay when I realized that piping information between commands in Shell is done through Ruby, making my beautiful shell scripts slow and hungry for memory.

I wanted something that would build out my shell scripts like Shell, but would stay in the shell where commands and pipes work quickly and smoothly.

Yikes. I'm not surprised. The library Works For Me in that the few places I use it and I haven't really developed it beyond my own needs.

Also, there are some differences I can't figure out how to avoid.

Ruby's Shellwords library does that. If you know of a better library for properly escaping shell-related strings, let me know!

Add this line to your application's Gemfile:

gem 'shellb'

And then execute:

$ bundle

Or install it yourself as:

$ gem install shellb

ShellB is intended to work similarly to Shell. There are a few differences:

1. All commands you intend to use must be defined via ShellB.def_system_command
2. Unlike Shell, ShellB will not run any commands on its own. You must either

• Call #run on a ShellB::Shell instance
• Call ShellB::Shell#run { <commands here> } which will immediately execute the script

See the examples below.

%w[a b c d e f g].each do |cmd|
  ShellB.def_system_command(cmd)
end

# Support Shell's #transact method -- my favorite way to build a script
shb = ShellB.new
script = shb.transact do
  a | b | c("--last", "--delimiter", "\t")
end
puts script # a | b | c --last --delimiter "\t"

# Invoke methods directly on ShellB::Shell instance
shb = ShellB.new
shb.a("--help") | shb.e("last")
puts shb.to_sh # => a --help | e last

# Run a script
shb = ShellB.new
shb.a("--help") | shb.e("last")
shb.run # creates a temporary script file and invokes it using Bash

# Immediately run a script after building it
ShellB.new.run do
  a | b
  c
end

# Support `cd` ala Shell
# NOT YET IMPLEMENTED
shb.cd("/tmp") do
  pwd
end # => (cd /tmp ; pwd)

# Handle Multiple Inputs into a Command
# Allow variable names as arguments
# NOT YET IMPLEMENTED
file1_csv = "/tmp/file1.csv"
file2_csv = "/tmp/file2.csv"
shb.transact do
  diff \
    < transact(do
        xsv("sort", file1_csv) | head
      end) \
    < transact({
        xsv("sort", file2_csv) | tail
      })
end # => diff <(xsv sort /tmp/file1.csv | head) <(xsv sort /tmp/file2.csv | tail)

Some ideas I'm toying with:

It might be handy to feed a hash to a command and have that generate the appropriate switches for a command.

Something like:

shb = ShellB.new
shb.transact do
  e(long_switch: "value", s: true)
end
puts shb.to_sh # => e --long-switch value -s

However, how do we handle some of the following?

• Underscore vs dash in long names?
  • E.g. does long_switch_name become --long-switch-name or --long_switch_name
• For long switches, do we include an equals sign if a value is included?
  • E.g. does long_switch_name: "value" become --long-switch-name=value or --long-switch-name value
• For switches without arguments, do we relegate those to an array only, or allow them in the hash?
  • E.g. does s: true become -s

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

As any good programmer, I wrote first and googled later. Here are some other projects that seem very similar to ShellB:

• https://github.com/jgoizueta/sys_cmd
• https://github.com/duncanbeevers/sheller
• https://github.com/fetlife/scallop
• https://github.com/quark-zju/easysh
• https://github.com/eropple/shellator
• https://github.com/petyosi/shellshot
• https://github.com/taccon/eksek

Bug reports and pull requests are welcome on GitHub at https://github.com/aguynamedryan/shellb.

The gem is available as open source under the terms of the MIT License.