Steel Overseer

A file watcher and development tool, similar to Ruby's Guard.

The main idea is that you have steeloverseer watch your files and then execute a series of shell commands in response. The first command to fail short circuits the series. The watched files can be selected using regular expressions and the commands may include capture groups.

Installation

Download and install the stack build tool.

stack install steeloverseer

This will create a binary deep inside ~/.stack/, and symlink to it at ~/.local/bin/sos.

Usage

See sos --help to get started:

Steel Overseer 2.0.2

Usage: sos [TARGET] [--rcfile ARG] [-c|--command COMMAND] [-p|--pattern PATTERN]
           [-e|--exclude PATTERN]
  A file watcher and development tool.

Available options:
  -h,--help                Show this help text
  TARGET                   Optional file or directory to watch for
                           changes. (default: ".")
  --rcfile ARG             Optional rcfile to read patterns and commands
                           from. (default: ".sosrc")
  -c,--command COMMAND     Add command to run on file event.
  -p,--pattern PATTERN     Add pattern to match on file path. Only relevant if
                           the target is a directory. (default: .*)
  -e,--exclude PATTERN     Add pattern to exclude matches on file path. Only
                           relevant if the target is a directory.

Patterns and Commands

Capture groups can be created with ( ) and captured variables can be referred to with \1, \2, etc. (\0 contains the entire match).

For example, for each change to a .c file in src/ (excluding files containing "_test"), we may want to compile the file and run its corresponding unit test:

sos src/ -c "gcc -c \0 -o obj/\1.o" -c "make test --filter=test/\1_test.c" -p "src/(.*)\.c" -e "_test"

Commands are run left-to-right, and one failed command will halt the entire pipeline.

The RCFile

As a shortcut, we may want to write the above only once and save it in .sosrc, which is an alternative to the command-line interface (yaml syntax):

- pattern: src/(.*)\.c
  exclude: _test
  commands:
  - gcc -c \0 -o obj/\1.o
  - make test --filter=test/\1_test.c

Then, we only need to run:

sos

to start watching the current directory. If you'd like to use multiple rcfiles, or just don't like the name .sosrc you can specify the rcfile on the command line like so:

sos --rcfile my-rcfile

Grammar

sosrc            := [entry]
entry            := {
                      pattern_entry,
                      exclude_entry?, -- Note: optional!
                      command_entry
                    }
pattern_entry    := "pattern" | "patterns" : value | [value]
exclude_entry    := "exclude" | "excludes" | "excluding" : value | [value]
command_entry    := "command" | "commands" : value | [value]
value            := [segment]
segment          := text_segment | var_segment
text_segment     := string
var_segment      := '\' integer

The .sosrc grammar is somewhat flexible with respect to the command specifications. Both singular and plural keys are allowed, and both strings and lists of strings are allowed for values.

Pipelining Explaned

Pipelines of commands are immediately canceled and re-run if a subsequent filesystem event triggers the same list of commands. Otherwise, commands are are enqueued and run sequentially to keep the terminal output clean and readable.

For example, we may wish to run hlint on any modified .hs file:

- pattern: .*\.hs
  command: hlint \0

We can modify foo.hs and trigger hlint foo.hs to run. During its execution, modifying bar.hs will enqueue hlint bar.hs, while modifying foo.hs again will re-run hlint foo.hs.