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ratelimit (your shell pipes!)

A tiny POSIX utility for rate limiting text lines piped through it.

Installation

To install from source, simply use:

make install

Another pleasant option is the nix package manager. I'm not actively maintaining this package, so I've kept it unlisted. Never-the-less, it's simple to pull this package into your configuration directly from GitHub:

pkgs.callPackage
  ( pkgs.fetchFromGitHub
    {
      owner = "rehno-lindeque";
      repo = "ratelimit-pipe";
      rev = "c9a61932a31a6ebeba3269b2c5ae4c1fb7202a05";
      sha256 = "16xr6zx0hv502d4a3mx4903l8zvmsn71krsizqbb0m5k83r9h9ac";
    }
  )
  {};

Usage

Usage: ratelimit [OPTION]
Example: { printf "a\nb\n" ; sleep 2; printf "c\nd"; sleep 1; printf "e\nf"; } | ratelimit -f0.8

        -f, --frequency         frequency of text lines relayed per second
        --help                  display this help text and exit

Ratelimited LiveReload

Here is a less contrived example using entr and reload-browser:

while true; do
find -name '*.html' | entr -d echo /_ | ratelimit --frequency 0.5 | while read l ; do reload-browser Firefox ; done
done

Or, alternatively, using inotify-tools:

inotifywait -qrm --event close_write . | grep --line-buffered '\.html$' | ratelimit --frequency 0.5 | while read l ; do reload-browser Firefox ; done

Here we filter on notifications for files matching the .html extension. Another common pattern to filter on might be grep --line-buffered \(\.js$\|\.html$\|\.css$\). If you'd like to handle each of these file exensions differently, put your while read l loop in a bash function with a case statement.

Automatically reload your Haskell REPL

The same trick can be used to reload your repl, combining your standard input (using cat -) with the inotifywait pipeline.

{ inotifywait -qrm --event close_write . | grep --line-buffered '\.hs$' | ratelimit --frequency 0.5 | sed -ue 's/.*/:reload/g' & cat -; } | ghci

However, since we are forking inotifywait as a child process it won't be killed automatically, so you probably will want to trap the exit / interrupt / terminate signal.

{ trap 'kill $(jobs -pr)' SIGINT SIGTERM EXIT; inotifywait -qrm --event close_write . | grep --line-buffered '\.hs$' | ratelimit --frequency 0.5 | sed -ue 's/.*/:reload/g' & cat -; } | ghci

Unfortunately the readline is broken by arrow keys etc when piping into ghci... but we can wrap it with our own:

{ trap 'kill $(jobs -pr)' SIGINT SIGTERM EXIT; inotifywait -qrm --event close_write . | grep --line-buffered '\.hs$' | ratelimit --frequency 0.5 | sed -ue 's/.*/:reload/g' & rlwrap -pWHITE -S "λ " -m cat -; } | ghci

Finally, if you are already using GHC 8, you may want to add the -freverse-errors flags to avoid the need to scroll up past a cascade of error messages.

{ trap 'kill $(jobs -pr)' SIGINT SIGTERM EXIT; inotifywait -qrm --event close_write . | grep --line-buffered '\.hs$' | ratelimit --frequency 0.5 | sed -ue 's/.*/:reload/g' & rlwrap -pWHITE -S "λ " -m cat -; } | ghci -freverse-errors

Contributing

I'm unlikely to add any new features to this utility, but please feel free to let me know if you would like to take over maintenance on this program.