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General purpose file previewer designed for Ranger, Lf to make scope.sh redundant

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Pistol

Introduction

Pistol is a file previewer for command line file managers such as Ranger, Lf and nnn, intended to replace the file previewer shell script scope.sh commonly used with Ranger and other previewing methods.

scope.sh is a Bash script that uses case switches and external programs to decide how to preview every file it encounters. It knows how to handle every file according to its MIME type and/or file extension using case switches and external programs. This design makes it hard to configure / maintain and it makes it slow for startup and heavy when running.

Pistol is a Go program (with (almost) 0 dependencies) and its MIME type detection is internal. Moreover, it features native preview support for almost any archive file and for text files along with syntax highlighting while scope.sh relies on external programs to do these basic tasks.

The following table lists Pistol’s native previewing support:

File/MIME Type Notes on implementation

text/*

Prints text files with syntax highlighting thanks to chroma.

Archives

Prints the contents of archive files using archiver.

In case Pistol encounters a MIME type it doesn’t know how to handle natively and you haven’t configured a program to handle it, it’ll print a general description of the file type it encountered. For example, the preview for an executable might be:

ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=a34861a1ae5358dc1079bc239df9dfe4830a8403, for GNU/Linux 3.2.0, not stripped

This feature is available out of the box just like the previews for the common mime types mentioned above.

See also the WiKi article: Pistol out in the Wild.

A Note on MIME type Detection

Some pure Go libraries provide MIME type detection. Here are the top search results I got using a common web search engine:

Pistol uses the last one which leverages the well known C library libmagic(3). I made this choice after experimenting with the other candidates and due to their lack of an extensive database such as libmagic(3) has, I chose magicmime.

Note that this choice also features compatibility with the standard command file which is available by default on most GNU/Linux distributions.[1]

A Note on Archive Previews

Pistol previews all archive / compression formats supported by the Go library archiver. Some formats do nothing but compression, meaning they operate on 1 file alone and some files are a combination of archive, compressed in a certain algorithm.

For example, a .gz file is a single file compressed with gzip. A .tar file is an uncompressed archive (collection) of files. A .tar.gz is a .tar file compressed using gzip.

When pistol encounters a single file compressed using a known compression algorithm, it doesn’t know how to handle its content, it displays the type of the archive. If a known compression algorithm has compressed a .tar file, Pistol lists the files themselves.

brotli compressed archives, (.tar.br) and Brotli compressed files (.br) are not detected by libmagic so Pistol doesn’t know how to handle them.[2]

Install

If someone has packaged Pistol for your distribution, you might find a package for of it linked in the WiKi.

If not, use the following instructions, or grab a statically compiled version of it from the releases page, available since version 0.3.1. The releases assets include also the manual page pistol.1.gz.

Warning
Currently, Darwin compatible binaries are not available there, but it should be possible to generate them via CI. All other binaries were cross compiled from my own x86_64 linux machine, using Nix' superb cross compilation support.
Note
For a statically compiled Pistol to be functional, it needs to read a libmagic database (usually found in /usr/share/misc/magic.mgc) and the static executable includes the contents of this database found on Nixpkgs' file package. The content of the magic.mgc database is copied to ~/.local/share/pistol/${libmagic-version}.mgc when you first run the executable. Hence using this executable might not be desirable due to this behaviour which a regular compilation of pistol does not include. This behaviour is compiled into pistol if you use go {build,install} with -tags EMBED_MAGIC_DB.

From Source

Since Pistol depends on magicmime, you’ll need a libmagic package installed. Please refer to this section in Magicmime’s README for the appropriate commands for every OS. In particular, if you installed libmagic using brew on a Darwin system, you may need to use the CGO_FLAGS environment variable to compile pistol. See #6 for more details.

Assuming you’ve installed libmagic properly and you have setup a Go environment, Use the following command to install Pistol to $GOPATH/bin/pistol:

Go 1.16 or later

go install github.com/doronbehar/pistol/cmd/pistol@latest

Go 1.15 or earlier

env CGO_ENABLED=1 GO111MODULE=on go get -u github.com/doronbehar/pistol/cmd/pistol

[3]

Besides libmagic, asciidoctor is also recommended, in order to compile the README as a manpage and install it. NixOS For instance, does it like this:

  # ...
  nativeBuildInputs = [
    installShellFiles
    asciidoctor
  ];
  postInstall = ''
    asciidoctor -b manpage -d manpage README.adoc
    installManPage pistol.1
  '';
  # ...

Link to currently evaluated file on NixOS. Packagers for other distros should do something similar.

Usage

$ pistol --help
Usage: pistol OPTIONS <file> [<extras> ...]

OPTIONS

-V, --version               Print version date and exit
-c, --config <config file>  configuration file to use (defaults to ~/.config/pistol/pistol.conf on Linux)
-h, --help                  print help and exit

ARGUMENTS

file                        the file to preview
extras                      extra arguments passed to the command

Integrations

Ranger / Lf

You can use Pistol as a file previewer in Ranger and Lf. For Ranger, set your preview_script in your rc.conf as follows:

set preview_script ~/.go/bin/pistol

The same goes for Lf, but in lfrc:

set previewer ~/.go/bin/pistol

fzf

If you use fzf to search for files, you can tell it to use pistol as the previewer. For example, the following command edits with your $EDITOR selected python file(s) using pistol as a previewer:

$EDITOR "$(find -name '*.py' | fzf --preview='pistol {}')"

Configuration

Although Pistol previews files of certain MIME types by default, it doesn’t force you to use these internal previewers for these MIME types. You can change this behaviour by writing a configuration file in ~/.config/pistol/pistol.conf (or $XDG_CONFIG_HOME/pistol/pistol.conf) On GNU systems, with the syntax as explained below.

Note
On OS X, this location defaults to: ~/Library/Preferences/pistol/pistol.conf, as the XDG specification imposes.

Syntax

You can configure preview commands according to file path or mime type regex. The 1st word may is always interpreted first as a mime type regex such as: text/*.

If a line is not matched but the 1st word is exactly fpath, then the 2nd argument is interpreted as a file path regex, such as: /var/src/.*/README.md.

On every line, whether you used fpath or not, the next arguments are the command’s arguments, where %pistol-filename% is substituted by pistol to the file at question. You’ll see more examples in the following sections.

Both regular expressions (for file paths and for mime types) are interpreted by the built-in library’s regexp.match. Please refer to this link for the full reference regarding syntax.

Matching Mime Types

You can inspect the MIME type of any file on a GNU/Linux OS and on Mac OS with the command file --mime-type <file>.

For example, say you wish to replace Pistol’s internal text previewer with that of bat’s, you’d put the following in your pistol.conf:

text/* bat --paging=never --color=always %pistol-filename%

Naturally, your configuration file overrides the internal previewers.

Here’s another example which features w3m as an HTML previewer:

text/html w3m -T text/html -dump %pistol-filename%

And here’s an example that leverages ls for printing directories’ contents:

inode/directory ls -l --color %pistol-filename%

Matching File Path

For example, say you wish to preview all files that reside in a certain ./bin directory with bat’s syntax highlighting for bash. You could use:

fpath /var/src/my-bash-project/bin/[^/]+$ bat --map-syntax :bash --paging=never --color=always %pistol-filename%

A Note on RegEx matching

When Pistol parses your configuration file, as soon as it finds a match be it a file path match or a mime type match, it stops parsing it and it invokes the command written on the rest of the line. Therefor, if you wish to use the examples from above which use w3m and bat, you’ll need to put w3m’s line before bat’s line. Since otherwise, text/* will be matched first and text/html won’t be checked at all.

Similarly, you’d probably want to put fpath lines at the top.

Of course that this is a mere example, the same may apply to any regular expressions you’d choose to match against.

For a list of the internal regular expressions tested against when Pistol reverts to its native previewers, read the file internal_writers/map.go.

More examples can be found in this WiKi page.

Quoting and Shell Piping

Pistol is pretty dumb when it parses your config, it splits all line by spaces, meaning that e.g:

application/json jq '.' %pistol-filename%

This will result in an error by jq:

jq: error: syntax error, unexpected INVALID_CHARACTER, expecting $end (Unix shell quoting issues?) at <top-level>, line 1:
'.'
jq: 1 compile error

Indicating that jq got a literal '.'. When you run in your shell jq '.' file.json you don’t get an error because your shell is stripping the quotes around .. However, Pistol is not smarter then your shell because if you’d try for example:

application/json jq '.[] | .' %pistol-filename%

That would be equivalent to running in the typical shell:

jq "\'.[]" "|" ".'" file.json

That’s because Pistol doesn’t consider your quotes as interesting instructions, it just splits words by spaces. Hence, to overcome this disability, you can use:

application/json sh: jq '.' %pistol-filename%

Thanks to the sh: keyword at the beginning of the command’s definition, the rest of the line goes straight as a single argument to sh -c.

You can worry not about quoting / escaping the rest of the line - it’s not like when you run e.g sh -c 'command' in your shell where you need to make sure single quotes are escaped or not used at all inside command.

More over, with sh: you can use shell pipes:

fpath .*.md$ sh: bat --paging=never --color=always %pistol-filename% | head -8

Passing arbitrary extra arguments to commands

Pistol is capable of passing extra arguments to commands if the config says so. The arguments %pistol-extra0%, %pistol-extra1% and so on, are substituted by the extra arguments given to pistol, if these present in invocation and if they are present in the config. Example usage:

With this config:

fpath /problematic-bz2/.*.bz2 bzip2 %pistol-filename% %pistol-extra0%
fpath /working-bz2/.*.bz2     bzip2 %pistol-filename%

Running:

pistol /problematic-bz2/example.bz2 --test

Will run bzip2 while testing the integrity of the compressed file. However, running:

pistol /working-bz2/example.bz2 --test

Will not pass the --test argument to bzip, due to %pistol-extra0 not present in the config for the files at /working-bz2. This feature is mainly present for usage with Lf and Ranger which can pass width height and x, y coordinates for image previews.

Here’s an example usage for image previews that works with Lf: [4]

image/.* pv %pistol-filename% %pistol-extra0% %pistol-extra1% %pistol-extra2% %pistol-extra3%

Environmental Variables

Pistol’s internal previewer for text files includes syntax highlighting thanks to the Go library chroma. You can customize Pistol’s syntax highlighting formatting and style through environmental variables.

Chroma Formatters

The term formatter refers to the way the given file is presented in the terminal. These include:

  • terminal: The default formatter that uses terminal control codes to change colors between every key word. This formatter has 8 colors and it’s the default.

  • terminal256: Same as terminal but with 256 colors available.

  • terminal16m: Same as terminal but with 24 Bits colors i.e True-Color.

Other formatters include json, and html but I’d be surprised if you’ll find them useful for Pistol’s purpose.

To tell Pistol to use a specific formatter, set PISTOL_CHROMA_FORMATTER in your environment, e.g:

export PISTOL_CHROMA_FORMATTER=terminal16m

Recent versions of Lf support 256 colors in its preview window. AFAIK, [5], Ranger supports 8 colors and Lf’s color256 isn’t enabled by default.

Therefor, I decided that it’ll be best to keep this variable unset in your general environment. If you do set color256 in your lfrc, you may feel free to set PISTOL_CHROMA_FORMATTER in your environment.

Chroma Styles

The term style refers to the set of colors used to print a given file. The chroma project documents all styles here and here.

The default style used by Pistol is pygments. To tell Pistol to use a specific style set PISTOL_CHROMA_STYLE in your environment, e.g:

export PISTOL_CHROMA_STYLE=monokai

Debugging

Can’t figure out way does Pistol acts the way he does? You can run pistol with:

env PISTOL_DEBUG=1 pistol test-file

And you should be able to see messages that may give you a clue.

NEWS


1. Considering Pistol’s indirect dependence on libmagic(3), I will never take the trouble to personally try and make it work on Windows natively. If you’ll succeed in the heroic task of compiling libmagic for Windows and teach magicmime to use it, please let me know.
3. env GO111MODULE=on is needed due to a recent bug / issue with Go, see #6 for more details. CGO_ENABLED=1 is needed for magicmime, see #76.
4. pv script refers to this script.
5. I don’t use Ranger anymore, ever since I moved to Lf. If you have evidence it does support 256 colors, let me know and I’ll change the default.

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General purpose file previewer designed for Ranger, Lf to make scope.sh redundant

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