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DESIGN.md

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ack3 design

Here we try to document ack's design, including design decisions that have already been made, so that we don't keep rehashing them.

Features that have been suggested but will not happen.

  • ack will not do replacing of text. It is not a replacement for sed.

  • ack will not edit files or invoke editors.

  • ack will not sort files by default.

Sorting the filenames requires reading in the entire directory of filenames before searching, and this can be a performance hit. In fact, it can kill ack entirely on directories with absurdly large numbers of files in them.

Design choices that are inviolate.

  • ack must run purely as Perl 5.10.1 using only core modules and File::Next.

No other modules may be used. That includes Moose or any Moose variants.

  • We don't use the Perl smartmatch operator.

  • ack must be able to be distributed through CPAN, using the App::Ack:: module tree.

  • ack must be able to be built as a single-file standalone file.

This file is intended to be able to be copied & pasted if necessary. It will not contain any characters out the range of [ -~]. See xt/coding-standards.t.

  • ack must be cross-platform. Specifically, it must run on Windows.

  • ack must not use any external tools.

  • The detection of whether a file is text or not is decided by Perl's -T operator.

  • Filetype detection is only through user-defined rules. ack will not shell out to file or any similar utilities.

  • ack must be able to be run under taint mode.

  • Use Perl's default file-handling as far as dealing with files of different encodings

  • ack must be able to be configured entirely from the command-line. ackrc files are merely collections of command-line switches.

Design questions that have been investigated

  • Would ack be faster if we used the integer pragma?

It seems not. Brian M. Carlson investigated this and reported his findings here: beyondgrep/ack2#398

There seemed to be no effect.

  • Why not make ack use /usr/bin/env in the shebang instead of /usr/bin/perl?

The Perl toolchain takes care of the shebang at install time.

Guiding principles

  • When deciding on ack's behavior, try to be grep-compatible if possible.