ripgrep/GUIDE.md

## User Guide

This guide is intended to give an elementary description of ripgrep and an
overview of its capabilities. This guide assumes that ripgrep is
[installed](README.md#installation)
and that readers have passing familiarity with using command line tools. This
also assumes a Unix-like system, although most commands are probably easily
translatable to any command line shell environment.


### Table of Contents

* [Basics](#basics)
* [Recursive search](#recursive-search)
* [Automatic filtering](#automatic-filtering)
* [Manual filtering: globs](#manual-filtering-globs)
* [Manual filtering: file types](#manual-filtering-file-types)
* [Replacements](#replacements)
* [Configuration file](#configuration-file)
* [File encoding](#file-encoding)
* [Binary data](#binary-data)
* [Preprocessor](#preprocessor)
* [Common options](#common-options)


### Basics

ripgrep is a command line tool that searches your files for patterns that
you give it. ripgrep behaves as if reading each file line by line. If a line
matches the pattern provided to ripgrep, then that line will be printed. If a
line does not match the pattern, then the line is not printed.

The best way to see how this works is with an example. To show an example, we
need something to search. Let's try searching ripgrep's source code. First
grab a ripgrep source archive from
https://github.com/BurntSushi/ripgrep/archive/0.7.1.zip
and extract it:

```
$ curl -LO https://github.com/BurntSushi/ripgrep/archive/0.7.1.zip
$ unzip 0.7.1.zip
$ cd ripgrep-0.7.1
$ ls
benchsuite  grep       tests         Cargo.toml       LICENSE-MIT
ci          ignore     wincolor      CHANGELOG.md     README.md
complete    pkg        appveyor.yml  compile          snapcraft.yaml
doc         src        build.rs      COPYING          UNLICENSE
globset     termcolor  Cargo.lock    HomebrewFormula
```

Let's try our first search by looking for all occurrences of the word `fast`
in `README.md`:

```
$ rg fast README.md
75:  faster than both. (N.B. It is not, strictly speaking, a "drop-in" replacement
88:  color and full Unicode support. Unlike GNU grep, `ripgrep` stays fast while
119:### Is it really faster than everything else?
124:Summarizing, `ripgrep` is fast because:
129:  optimizations to make searching very fast.
```

(**Note:** If you see an error message from ripgrep saying that it didn't
search any files, then re-run ripgrep with the `--debug` flag. One likely cause
of this is that you have a `*` rule in a `$HOME/.gitignore` file.)

So what happened here? ripgrep read the contents of `README.md`, and for each
line that contained `fast`, ripgrep printed it to your terminal. ripgrep also
included the line number for each line by default. If your terminal supports
colors, then your output might actually look something like this screenshot:

[![A screenshot of a sample search ripgrep](https://burntsushi.net/stuff/ripgrep-guide-sample.png)](https://burntsushi.net/stuff/ripgrep-guide-sample.png)

In this example, we searched for something called a "literal" string. This
means that our pattern was just some normal text that we asked ripgrep to
find. But ripgrep supports the ability to specify patterns via [regular
expressions](https://en.wikipedia.org/wiki/Regular_expression). As an example,
what if we wanted to find all lines have a word that contains `fast` followed
by some number of other letters?

```
$ rg 'fast\w+' README.md
75:  faster than both. (N.B. It is not, strictly speaking, a "drop-in" replacement
119:### Is it really faster than everything else?
```

In this example, we used the pattern `fast\w+`. This pattern tells ripgrep to
look for any lines containing the letters `fast` followed by *one or more*
word-like characters. Namely, `\w` matches characters that compose words (like
`a` and `L` but unlike `.` and ` `). The `+` after the `\w` means, "match the
previous pattern one or more times." This means that the word `fast` won't
match because there are no word characters following the final `t`. But a word
like `faster` will. `faste` would also match!

Here's a different variation on this same theme:

```
$ rg 'fast\w*' README.md
75:  faster than both. (N.B. It is not, strictly speaking, a "drop-in" replacement
88:  color and full Unicode support. Unlike GNU grep, `ripgrep` stays fast while
119:### Is it really faster than everything else?
124:Summarizing, `ripgrep` is fast because:
129:  optimizations to make searching very fast.
```

In this case, we used `fast\w*` for our pattern instead of `fast\w+`. The `*`
means that it should match *zero* or more times. In this case, ripgrep will
print the same lines as the pattern `fast`, but if your terminal supports
colors, you'll notice that `faster` will be highlighted instead of just the
`fast` prefix.

It is beyond the scope of this guide to provide a full tutorial on regular
expressions, but ripgrep's specific syntax is documented here:
https://docs.rs/regex/*/regex/#syntax


### Recursive search

In the previous section, we showed how to use ripgrep to search a single file.
In this section, we'll show how to use ripgrep to search an entire directory
of files. In fact, *recursively* searching your current working directory is
the default mode of operation for ripgrep, which means doing this is very
simple.

Using our unzipped archive of ripgrep source code, here's how to find all
function definitions whose name is `write`:

```
$ rg 'fn write\('
src/printer.rs
469:    fn write(&mut self, buf: &[u8]) {

termcolor/src/lib.rs
227:    fn write(&mut self, b: &[u8]) -> io::Result<usize> {
250:    fn write(&mut self, b: &[u8]) -> io::Result<usize> {
428:    fn write(&mut self, b: &[u8]) -> io::Result<usize> { self.wtr.write(b) }
441:    fn write(&mut self, b: &[u8]) -> io::Result<usize> { self.wtr.write(b) }
454:    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
511:    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
848:    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
915:    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
949:    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
1114:    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
1348:    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
1353:    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
```

(**Note:** We escape the `(` here because `(` has special significance inside
regular expressions. You could also use `rg -F 'fn write('` to achieve the
same thing, where `-F` interprets your pattern as a literal string instead of
a regular expression.)

In this example, we didn't specify a file at all. Instead, ripgrep defaulted
to searching your current directory in the absence of a path. In general,
`rg foo` is equivalent to `rg foo ./`.

This particular search showed us results in both the `src` and `termcolor`
directories. The `src` directory is the core ripgrep code where as `termcolor`
is a dependency of ripgrep (and is used by other tools). What if we only wanted
to search core ripgrep code? Well, that's easy, just specify the directory you
want:

```
$ rg 'fn write\(' src
src/printer.rs
469:    fn write(&mut self, buf: &[u8]) {
```

Here, ripgrep limited its search to the `src` directory. Another way of doing
this search would be to `cd` into the `src` directory and simply use `rg 'fn
write\('` again.


### Automatic filtering

After recursive search, ripgrep's most important feature is what it *doesn't*
search. By default, when you search a directory, ripgrep will ignore all of
the following:

1. Files and directories that match glob patterns in these three categories:
      1. `.gitignore` globs (including global and repo-specific globs). This
         includes `.gitignore` files in parent directories that are part of the
         same `git` repository. (Unless the `--no-require-git` flag is given.)
      2. `.ignore` globs, which take precedence over all gitignore globs
         when there's a conflict. This includes `.ignore` files in parent
         directories.
      3. `.rgignore` globs, which take precedence over all `.ignore` globs
         when there's a conflict. This includes `.rgignore` files in parent
         directories.
2. Hidden files and directories.
3. Binary files. (ripgrep considers any file with a `NUL` byte to be binary.)
4. Symbolic links aren't followed.

All of these things can be toggled using various flags provided by ripgrep:

1. You can disable all ignore-related filtering with the `--no-ignore` flag.
2. Hidden files and directories can be searched with the `--hidden` (`-.` for
short) flag.
3. Binary files can be searched via the `--text` (`-a` for short) flag.
   Be careful with this flag! Binary files may emit control characters to your
   terminal, which might cause strange behavior.
4. ripgrep can follow symlinks with the `--follow` (`-L` for short) flag.

As a special convenience, ripgrep also provides a flag called `--unrestricted`
(`-u` for short). Repeated uses of this flag will cause ripgrep to disable
more and more of its filtering. That is, `-u` will disable `.gitignore`
handling, `-uu` will search hidden files and directories and `-uuu` will search
binary files. This is useful when you're using ripgrep and you aren't sure
whether its filtering is hiding results from you. Tacking on a couple `-u`
flags is a quick way to find out. (Use the `--debug` flag if you're still
perplexed, and if that doesn't help,
[file an issue](https://github.com/BurntSushi/ripgrep/issues/new).)

ripgrep's `.gitignore` handling actually goes a bit beyond just `.gitignore`
files. ripgrep will also respect repository specific rules found in
`$GIT_DIR/info/exclude`, as well as any global ignore rules in your
`core.excludesFile` (which is usually `$XDG_CONFIG_HOME/git/ignore` on
Unix-like systems).

Sometimes you want to search files that are in your `.gitignore`, so it is
possible to specify additional ignore rules or overrides in a `.ignore`
(application agnostic) or `.rgignore` (ripgrep specific) file.

For example, let's say you have a `.gitignore` file that looks like this:

```
log/
```

This generally means that any `log` directory won't be tracked by `git`.
However, perhaps it contains useful output that you'd like to include in your
searches, but you still don't want to track it in `git`. You can achieve this
by creating a `.ignore` file in the same directory as the `.gitignore` file
with the following contents:

```
!log/
```

ripgrep treats `.ignore` files with higher precedence than `.gitignore` files
(and treats `.rgignore` files with higher precedence than `.ignore` files).
This means ripgrep will see the `!log/` whitelist rule first and search that
directory.

Like `.gitignore`, a `.ignore` file can be placed in any directory. Its rules
will be processed with respect to the directory it resides in, just like
`.gitignore`.

To process `.gitignore` and `.ignore` files case insensitively, use the flag
`--ignore-file-case-insensitive`. This is especially useful on case insensitive
file systems like those on Windows and macOS. Note though that this can come
with a significant performance penalty, and is therefore disabled by default.

For a more in depth description of how glob patterns in a `.gitignore` file
are interpreted, please see `man gitignore`.


### Manual filtering: globs

In the previous section, we talked about ripgrep's filtering that it does by
default. It is "automatic" because it reacts to your environment. That is, it
uses already existing `.gitignore` files to produce more relevant search
results.

In addition to automatic filtering, ripgrep also provides more manual or ad hoc
filtering. This comes in two varieties: additional glob patterns specified in
your ripgrep commands and file type filtering. This section covers glob
patterns while the next section covers file type filtering.

In our ripgrep source code (see [Basics](#basics) for instructions on how to
get a source archive to search), let's say we wanted to see which things depend
on `clap`, our argument parser.

We could do this:

```
$ rg clap
[lots of results]
```

But this shows us many things, and we're only interested in where we wrote
`clap` as a dependency. Instead, we could limit ourselves to TOML files, which
is how dependencies are communicated to Rust's build tool, Cargo:

```
$ rg clap -g '*.toml'
Cargo.toml
35:clap = "2.26"
51:clap = "2.26"
```

The `-g '*.toml'` syntax says, "make sure every file searched matches this
glob pattern." Note that we put `'*.toml'` in single quotes to prevent our
shell from expanding the `*`.

If we wanted, we could tell ripgrep to search anything *but* `*.toml` files:

```
$ rg clap -g '!*.toml'
[lots of results]
```

This will give you a lot of results again as above, but they won't include
files ending with `.toml`. Note that the use of a `!` here to mean "negation"
is a bit non-standard, but it was chosen to be consistent with how globs in
`.gitignore` files are written. (Although, the meaning is reversed. In
`.gitignore` files, a `!` prefix means whitelist, and on the command line, a
`!` means blacklist.)

Globs are interpreted in exactly the same way as `.gitignore` patterns. That
is, later globs will override earlier globs. For example, the following command
will search only `*.toml` files:

```
$ rg clap -g '!*.toml' -g '*.toml'
```

Interestingly, reversing the order of the globs in this case will match
nothing, since the presence of at least one non-blacklist glob will institute a
requirement that every file searched must match at least one glob. In this
case, the blacklist glob takes precedence over the previous glob and prevents
any file from being searched at all!


### Manual filtering: file types

Over time, you might notice that you use the same glob patterns over and over.
For example, you might find yourself doing a lot of searches where you only
want to see results for Rust files:

```
$ rg 'fn run' -g '*.rs'
```

Instead of writing out the glob every time, you can use ripgrep's support for
file types:

```
$ rg 'fn run' --type rust
```

or, more succinctly,

```
$ rg 'fn run' -trust
```

The way the `--type` flag functions is simple. It acts as a name that is
assigned to one or more globs that match the relevant files. This lets you
write a single type that might encompass a broad range of file extensions. For
example, if you wanted to search C files, you'd have to check both C source
files and C header files:

```
$ rg 'int main' -g '*.{c,h}'
```

or you could just use the C file type:

```
$ rg 'int main' -tc
```

Just as you can write blacklist globs, you can blacklist file types too:

```
$ rg clap --type-not rust
```

or, more succinctly,

```
$ rg clap -Trust
```

That is, `-t` means "include files of this type" where as `-T` means "exclude
files of this type."

To see the globs that make up a type, run `rg --type-list`:

```
$ rg --type-list | rg '^make:'
make: *.mak, *.mk, GNUmakefile, Gnumakefile, Makefile, gnumakefile, makefile
```

By default, ripgrep comes with a bunch of pre-defined types. Generally, these
types correspond to well known public formats. But you can define your own
types as well. For example, perhaps you frequently search "web" files, which
consist of JavaScript, HTML and CSS:

```
$ rg --type-add 'web:*.html' --type-add 'web:*.css' --type-add 'web:*.js' -tweb title
```

or, more succinctly,

```
$ rg --type-add 'web:*.{html,css,js}' -tweb title
```

The above command defines a new type, `web`, corresponding to the glob
`*.{html,css,js}`. It then applies the new filter with `-tweb` and searches for
the pattern `title`. If you ran

```
$ rg --type-add 'web:*.{html,css,js}' --type-list
```

Then you would see your `web` type show up in the list, even though it is not
part of ripgrep's built-in types.

It is important to stress here that the `--type-add` flag only applies to the
current command. It does not add a new file type and save it somewhere in a
persistent form. If you want a type to be available in every ripgrep command,
then you should either create a shell alias:

```
alias rg="rg --type-add 'web:*.{html,css,js}'"
```

or add `--type-add=web:*.{html,css,js}` to your ripgrep configuration file.
([Configuration files](#configuration-file) are covered in more detail later.)

#### The special `all` file type

A special option supported by the `--type` flag is `all`. `--type all` looks
for a match in any of the supported file types listed by `--type-list`,
including those added on the command line using `--type-add`. It's equivalent
to the command `rg --type agda --type asciidoc --type asm ...`, where `...`
stands for a list of `--type` flags for the rest of the types in `--type-list`.

As an example, let's suppose you have a shell script in your current directory,
`my-shell-script`, which includes a shell library, `my-shell-library.bash`.
Both `rg --type sh` and `rg --type all` would only search for matches in
`my-shell-library.bash`, not `my-shell-script`, because the globs matched
by the `sh` file type don't include files without an extension. On the
other hand, `rg --type-not all` would search `my-shell-script` but not
`my-shell-library.bash`.

### Replacements

ripgrep provides a limited ability to modify its output by replacing matched
text with some other text. This is easiest to explain with an example. Remember
when we searched for the word `fast` in ripgrep's README?

```
$ rg fast README.md
75:  faster than both. (N.B. It is not, strictly speaking, a "drop-in" replacement
88:  color and full Unicode support. Unlike GNU grep, `ripgrep` stays fast while
119:### Is it really faster than everything else?
124:Summarizing, `ripgrep` is fast because:
129:  optimizations to make searching very fast.
```

What if we wanted to *replace* all occurrences of `fast` with `FAST`? That's
easy with ripgrep's `--replace` flag:

```
$ rg fast README.md --replace FAST
75:  FASTer than both. (N.B. It is not, strictly speaking, a "drop-in" replacement
88:  color and full Unicode support. Unlike GNU grep, `ripgrep` stays FAST while
119:### Is it really FASTer than everything else?
124:Summarizing, `ripgrep` is FAST because:
129:  optimizations to make searching very FAST.
```

or, more succinctly,

```
$ rg fast README.md -r FAST
[snip]
```

In essence, the `--replace` flag applies *only* to the matching portion of text
in the output. If you instead wanted to replace an entire line of text, then
you need to include the entire line in your match. For example:

```
$ rg '^.*fast.*$' README.md -r FAST
75:FAST
88:FAST
119:FAST
124:FAST
129:FAST
```

Alternatively, you can combine the `--only-matching` (or `-o` for short) with
the `--replace` flag to achieve the same result:

```
$ rg fast README.md --only-matching --replace FAST
75:FAST
88:FAST
119:FAST
124:FAST
129:FAST
```

or, more succinctly,

```
$ rg fast README.md -or FAST
[snip]
```

Finally, replacements can include capturing groups. For example, let's say
we wanted to find all occurrences of `fast` followed by another word and
join them together with a dash. The pattern we might use for that is
`fast\s+(\w+)`, which matches `fast`, followed by any amount of whitespace,
followed by any number of "word" characters. We put the `\w+` in a "capturing
group" (indicated by parentheses) so that we can reference it later in our
replacement string. For example:

```
$ rg 'fast\s+(\w+)' README.md -r 'fast-$1'
88:  color and full Unicode support. Unlike GNU grep, `ripgrep` stays fast-while
124:Summarizing, `ripgrep` is fast-because:
```

Our replacement string here, `fast-$1`, consists of `fast-` followed by the
contents of the capturing group at index `1`. (Capturing groups actually start
at index 0, but the `0`th capturing group always corresponds to the entire
match. The capturing group at index `1` always corresponds to the first
explicit capturing group found in the regex pattern.)

Capturing groups can also be named, which is sometimes more convenient than
using the indices. For example, the following command is equivalent to the
above command:

```
$ rg 'fast\s+(?P<word>\w+)' README.md -r 'fast-$word'
88:  color and full Unicode support. Unlike GNU grep, `ripgrep` stays fast-while
124:Summarizing, `ripgrep` is fast-because:
```

It is important to note that ripgrep **will never modify your files**. The
`--replace` flag only controls ripgrep's output. (And there is no flag to let
you do a replacement in a file.)


### Configuration file

It is possible that ripgrep's default options aren't suitable in every case.
For that reason, and because shell aliases aren't always convenient, ripgrep
supports configuration files.

Setting up a configuration file is simple. ripgrep will not look in any
predetermined directory for a config file automatically. Instead, you need to
set the `RIPGREP_CONFIG_PATH` environment variable to the file path of your
config file. Once the environment variable is set, open the file and just type
in the flags you want set automatically. There are only two rules for
describing the format of the config file:

1. Every line is a shell argument, after trimming whitespace.
2. Lines starting with `#` (optionally preceded by any amount of whitespace)
are ignored.

In particular, there is no escaping. Each line is given to ripgrep as a single
command line argument verbatim.

Here's an example of a configuration file, which demonstrates some of the
formatting peculiarities:

```
$ cat $HOME/.ripgreprc
# Don't let ripgrep vomit really long lines to my terminal, and show a preview.
--max-columns=150
--max-columns-preview

# Add my 'web' type.
--type-add
web:*.{html,css,js}*

# Search hidden files / directories (e.g. dotfiles) by default
--hidden

# Using glob patterns to include/exclude files or folders
--glob=!.git/*

# or
--glob
!.git/*

# Set the colors.
--colors=line:none
--colors=line:style:bold

# Because who cares about case!?
--smart-case
```

When we use a flag that has a value, we either put the flag and the value on
the same line but delimited by an `=` sign (e.g., `--max-columns=150`), or we
put the flag and the value on two different lines. This is because ripgrep's
argument parser knows to treat the single argument `--max-columns=150` as a
flag with a value, but if we had written `--max-columns 150` in our
configuration file, then ripgrep's argument parser wouldn't know what to do
with it.

Putting the flag and value on different lines is exactly equivalent and is a
matter of style.

Comments are encouraged so that you remember what the config is doing. Empty
lines are OK too.

So let's say you're using the above configuration file, but while you're at a
terminal, you really want to be able to see lines longer than 150 columns. What
do you do? Thankfully, all you need to do is pass `--max-columns 0` (or `-M0`
for short) on the command line, which will override your configuration file's
setting. This works because ripgrep's configuration file is *prepended* to the
explicit arguments you give it on the command line. Since flags given later
override flags given earlier, everything works as expected. This works for most
other flags as well, and each flag's documentation states which other flags
override it.

If you're confused about what configuration file ripgrep is reading arguments
from, then running ripgrep with the `--debug` flag should help clarify things.
The debug output should note what config file is being loaded and the arguments
that have been read from the configuration.

Finally, if you want to make absolutely sure that ripgrep *isn't* reading a
configuration file, then you can pass the `--no-config` flag, which will always
prevent ripgrep from reading extraneous configuration from the environment,
regardless of what other methods of configuration are added to ripgrep in the
future.


### File encoding

[Text encoding](https://en.wikipedia.org/wiki/Character_encoding) is a complex
topic, but we can try to summarize its relevancy to ripgrep:

* Files are generally just a bundle of bytes. There is no reliable way to know
  their encoding.
* Either the encoding of the pattern must match the encoding of the files being
  searched, or a form of transcoding must be performed that converts either the
  pattern or the file to the same encoding as the other.
* ripgrep tends to work best on plain text files, and among plain text files,
  the most popular encodings likely consist of ASCII, latin1 or UTF-8. As
  a special exception, UTF-16 is prevalent in Windows environments

In light of the above, here is how ripgrep behaves when `--encoding auto` is
given, which is the default:

* All input is assumed to be ASCII compatible (which means every byte that
  corresponds to an ASCII codepoint actually is an ASCII codepoint). This
  includes ASCII itself, latin1 and UTF-8.
* ripgrep works best with UTF-8. For example, ripgrep's regular expression
  engine supports Unicode features. Namely, character classes like `\w` will
  match all word characters by Unicode's definition and `.` will match any
  Unicode codepoint instead of any byte. These constructions assume UTF-8,
  so they simply won't match when they come across bytes in a file that aren't
  UTF-8.
* To handle the UTF-16 case, ripgrep will do something called "BOM sniffing"
  by default. That is, the first three bytes of a file will be read, and if
  they correspond to a UTF-16 BOM, then ripgrep will transcode the contents of
  the file from UTF-16 to UTF-8, and then execute the search on the transcoded
  version of the file. (This incurs a performance penalty since transcoding
  is needed in addition to regex searching.) If the file contains invalid
  UTF-16, then the Unicode replacement codepoint is substituted in place of
  invalid code units.
* To handle other cases, ripgrep provides a `-E/--encoding` flag, which permits
  you to specify an encoding from the
  [Encoding Standard](https://encoding.spec.whatwg.org/#concept-encoding-get).
  ripgrep will assume *all* files searched are the encoding specified (unless
  the file has a BOM) and will perform a transcoding step just like in the
  UTF-16 case described above.

By default, ripgrep will not require its input be valid UTF-8. That is, ripgrep
can and will search arbitrary bytes. The key here is that if you're searching
content that isn't UTF-8, then the usefulness of your pattern will degrade. If
you're searching bytes that aren't ASCII compatible, then it's likely the
pattern won't find anything. With all that said, this mode of operation is
important, because it lets you find ASCII or UTF-8 *within* files that are
otherwise arbitrary bytes.

As a special case, the `-E/--encoding` flag supports the value `none`, which
will completely disable all encoding related logic, including BOM sniffing.
When `-E/--encoding` is set to `none`, ripgrep will search the raw bytes of
the underlying file with no transcoding step. For example, here's how you might
search the raw UTF-16 encoding of the string `Шерлок`:

```
$ rg '(?-u)\(\x045\x04@\x04;\x04>\x04:\x04' -E none -a some-utf16-file
```

Of course, that's just an example meant to show how one can drop down into
raw bytes. Namely, the simpler command works as you might expect automatically:

```
$ rg 'Шерлок' some-utf16-file
```

Finally, it is possible to disable ripgrep's Unicode support from within the
regular expression. For example, let's say you wanted `.` to match any byte
rather than any Unicode codepoint. (You might want this while searching a
binary file, since `.` by default will not match invalid UTF-8.) You could do
this by disabling Unicode via a regular expression flag:

```
$ rg '(?-u:.)'
```

This works for any part of the pattern. For example, the following will find
any Unicode word character followed by any ASCII word character followed by
another Unicode word character:

```
$ rg '\w(?-u:\w)\w'
```


### Binary data

In addition to skipping hidden files and files in your `.gitignore` by default,
ripgrep also attempts to skip binary files. ripgrep does this by default
because binary files (like PDFs or images) are typically not things you want to
search when searching for regex matches. Moreover, if content in a binary file
did match, then it's possible for undesirable binary data to be printed to your
terminal and wreak havoc.

Unfortunately, unlike skipping hidden files and respecting your `.gitignore`
rules, a file cannot as easily be classified as binary. In order to figure out
whether a file is binary, the most effective heuristic that balances
correctness with performance is to simply look for `NUL` bytes. At that point,
the determination is simple: a file is considered "binary" if and only if it
contains a `NUL` byte somewhere in its contents.

The issue is that while most binary files will have a `NUL` byte toward the
beginning of its contents, this is not necessarily true. The `NUL` byte might
be the very last byte in a large file, but that file is still considered
binary. While this leads to a fair amount of complexity inside ripgrep's
implementation, it also results in some unintuitive user experiences.

At a high level, ripgrep operates in three different modes with respect to
binary files:

1. The default mode is to attempt to remove binary files from a search
   completely. This is meant to mirror how ripgrep removes hidden files and
   files in your `.gitignore` automatically. That is, as soon as a file is
   detected as binary, searching stops. If a match was already printed (because
   it was detected long before a `NUL` byte), then ripgrep will print a warning
   message indicating that the search stopped prematurely. This default mode
   **only applies to files searched by ripgrep as a result of recursive
   directory traversal**, which is consistent with ripgrep's other automatic
   filtering. For example, `rg foo .file` will search `.file` even though it
   is hidden. Similarly, `rg foo binary-file` will search `binary-file` in
   "binary" mode automatically.
2. Binary mode is similar to the default mode, except it will not always
   stop searching after it sees a `NUL` byte. Namely, in this mode, ripgrep
   will continue searching a file that is known to be binary until the first
   of two conditions is met: 1) the end of the file has been reached or 2) a
   match is or has been seen. This means that in binary mode, if ripgrep
   reports no matches, then there are no matches in the file. When a match does
   occur, ripgrep prints a message similar to one it prints when in its default
   mode indicating that the search has stopped prematurely. This mode can be
   forcefully enabled for all files with the `--binary` flag. The purpose of
   binary mode is to provide a way to discover matches in all files, but to
   avoid having binary data dumped into your terminal.
3. Text mode completely disables all binary detection and searches all files
   as if they were text. This is useful when searching a file that is
   predominantly text but contains a `NUL` byte, or if you are specifically
   trying to search binary data. This mode can be enabled with the `-a/--text`
   flag. Note that when using this mode on very large binary files, it is
   possible for ripgrep to use a lot of memory.

Unfortunately, there is one additional complexity in ripgrep that can make it
difficult to reason about binary files. That is, the way binary detection works
depends on the way that ripgrep searches your files. Specifically:

* When ripgrep uses memory maps, then binary detection is only performed on the
  first few kilobytes of the file in addition to every matching line.
* When ripgrep doesn't use memory maps, then binary detection is performed on
  all bytes searched.

This means that whether a file is detected as binary or not can change based
on the internal search strategy used by ripgrep. If you prefer to keep
ripgrep's binary file detection consistent, then you can disable memory maps
via the `--no-mmap` flag. (The cost will be a small performance regression when
searching very large files on some platforms.)


### Preprocessor

In ripgrep, a preprocessor is any type of command that can be run to transform
the input of every file before ripgrep searches it. This makes it possible to
search virtually any kind of content that can be automatically converted to
text without having to teach ripgrep how to read said content.

One common example is searching PDFs. PDFs are first and foremost meant to be
displayed to users. But PDFs often have text streams in them that can be useful
to search. In our case, we want to search Bruce Watson's excellent
dissertation,
[Taxonomies and Toolkits of Regular Language Algorithms](https://burntsushi.net/stuff/1995-watson.pdf).
After downloading it, let's try searching it:

```
$ rg 'The Commentz-Walter algorithm' 1995-watson.pdf
$
```

Surely, a dissertation on regular language algorithms would mention
Commentz-Walter. Indeed it does, but our search isn't picking it up because
PDFs are a binary format, and the text shown in the PDF may not be encoded as
simple contiguous UTF-8. Namely, even passing the `-a/--text` flag to ripgrep
will not make our search work.

One way to fix this is to convert the PDF to plain text first. This won't work
well for all PDFs, but does great in a lot of cases. (Note that the tool we
use, `pdftotext`, is part of the [poppler](https://poppler.freedesktop.org)
PDF rendering library.)

```
$ pdftotext 1995-watson.pdf > 1995-watson.txt
$ rg 'The Commentz-Walter algorithm' 1995-watson.txt
316:The Commentz-Walter algorithms : : : : : : : : : : : : : : :
7165:4.4 The Commentz-Walter algorithms
10062:in input string S , we obtain the Boyer-Moore algorithm. The Commentz-Walter algorithm
17218:The Commentz-Walter algorithm (and its variants) displayed more interesting behaviour,
17249:Aho-Corasick algorithms are used extensively. The Commentz-Walter algorithms are used
17297: The Commentz-Walter algorithms (CW). In all versions of the CW algorithms, a common program skeleton is used with di erent shift functions. The CW algorithms are
```

But having to explicitly convert every file can be a pain, especially when you
have a directory full of PDF files. Instead, we can use ripgrep's preprocessor
feature to search the PDF. ripgrep's `--pre` flag works by taking a single
command name and then executing that command for every file that it searches.
ripgrep passes the file path as the first and only argument to the command and
also sends the contents of the file to stdin. So let's write a simple shell
script that wraps `pdftotext` in a way that conforms to this interface:

```
$ cat preprocess
#!/bin/sh

exec pdftotext - -
```

With `preprocess` in the same directory as `1995-watson.pdf`, we can now use it
to search the PDF:

```
$ rg --pre ./preprocess 'The Commentz-Walter algorithm' 1995-watson.pdf
316:The Commentz-Walter algorithms : : : : : : : : : : : : : : :
7165:4.4 The Commentz-Walter algorithms
10062:in input string S , we obtain the Boyer-Moore algorithm. The Commentz-Walter algorithm
17218:The Commentz-Walter algorithm (and its variants) displayed more interesting behaviour,
17249:Aho-Corasick algorithms are used extensively. The Commentz-Walter algorithms are used
17297: The Commentz-Walter algorithms (CW). In all versions of the CW algorithms, a common program skeleton is used with di erent shift functions. The CW algorithms are
```

Note that `preprocess` must be resolvable to a command that ripgrep can read.
The simplest way to do this is to put your preprocessor command in a directory
that is in your `PATH` (or equivalent), or otherwise use an absolute path.

As a bonus, this turns out to be quite a bit faster than other specialized PDF
grepping tools:

```
$ time rg --pre ./preprocess 'The Commentz-Walter algorithm' 1995-watson.pdf -c
6

real    0.697
user    0.684
sys     0.007
maxmem  16 MB
faults  0

$ time pdfgrep 'The Commentz-Walter algorithm' 1995-watson.pdf -c
6

real    1.336
user    1.310
sys     0.023
maxmem  16 MB
faults  0
```

If you wind up needing to search a lot of PDFs, then ripgrep's parallelism can
make the speed difference even greater.

#### A more robust preprocessor

One of the problems with the aforementioned preprocessor is that it will fail
if you try to search a file that isn't a PDF:

```
$ echo foo > not-a-pdf
$ rg --pre ./preprocess 'The Commentz-Walter algorithm' not-a-pdf
not-a-pdf: preprocessor command failed: '"./preprocess" "not-a-pdf"':
-------------------------------------------------------------------------------
Syntax Warning: May not be a PDF file (continuing anyway)
Syntax Error: Couldn't find trailer dictionary
Syntax Error: Couldn't find trailer dictionary
Syntax Error: Couldn't read xref table
```

To fix this, we can make our preprocessor script a bit more robust by only
running `pdftotext` when we think the input is a non-empty PDF:

```
$ cat preprocessor
#!/bin/sh

case "$1" in
*.pdf)
  # The -s flag ensures that the file is non-empty.
  if [ -s "$1" ]; then
    exec pdftotext - -
  else
    exec cat
  fi
  ;;
*)
  exec cat
  ;;
esac
```

We can even extend our preprocessor to search other kinds of files. Sometimes
we don't always know the file type from the file name, so we can use the `file`
utility to "sniff" the type of the file based on its contents:

```
$ cat processor
#!/bin/sh

case "$1" in
*.pdf)
  # The -s flag ensures that the file is non-empty.
  if [ -s "$1" ]; then
    exec pdftotext - -
  else
    exec cat
  fi
  ;;
*)
  case $(file "$1") in
  *Zstandard*)
    exec pzstd -cdq
    ;;
  *)
    exec cat
    ;;
  esac
  ;;
esac
```

#### Reducing preprocessor overhead

There is one more problem with the above approach: it requires running a
preprocessor for every single file that ripgrep searches. If every file needs
a preprocessor, then this is OK. But if most don't, then this can substantially
slow down searches because of the overhead of launching new processors. You
can avoid this by telling ripgrep to only invoke the preprocessor when the file
path matches a glob. For example, consider the performance difference even when
searching a repository as small as ripgrep's:

```
$ time rg --pre pre-rg 'fn is_empty' -c
crates/globset/src/lib.rs:1
crates/matcher/src/lib.rs:2
crates/ignore/src/overrides.rs:1
crates/ignore/src/gitignore.rs:1
crates/ignore/src/types.rs:1

real    0.138
user    0.485
sys     0.209
maxmem  7 MB
faults  0

$ time rg --pre pre-rg --pre-glob '*.pdf' 'fn is_empty' -c
crates/globset/src/lib.rs:1
crates/ignore/src/types.rs:1
crates/ignore/src/gitignore.rs:1
crates/ignore/src/overrides.rs:1
crates/matcher/src/lib.rs:2

real    0.008
user    0.010
sys     0.002
maxmem  7 MB
faults  0
```


### Common options

ripgrep has a lot of flags. Too many to keep in your head at once. This section
is intended to give you a sampling of some of the most important and frequently
used options that will likely impact how you use ripgrep on a regular basis.

* `-h`: Show ripgrep's condensed help output.
* `--help`: Show ripgrep's longer form help output. (Nearly what you'd find in
  ripgrep's man page, so pipe it into a pager!)
* `-i/--ignore-case`: When searching for a pattern, ignore case differences.
  That is `rg -i fast` matches `fast`, `fASt`, `FAST`, etc.
* `-S/--smart-case`: This is similar to `--ignore-case`, but disables itself
  if the pattern contains any uppercase letters. Usually this flag is put into
  alias or a config file.
* `-F/--fixed-strings`: Disable regular expression matching and treat the pattern
   as a literal string.
* `-w/--word-regexp`: Require that all matches of the pattern be surrounded
  by word boundaries. That is, given `pattern`, the `--word-regexp` flag will
  cause ripgrep to behave as if `pattern` were actually `\b(?:pattern)\b`.
* `-c/--count`: Report a count of total matched lines.
* `--files`: Print the files that ripgrep *would* search, but don't actually
  search them.
* `-a/--text`: Search binary files as if they were plain text.
* `-U/--multiline`: Permit matches to span multiple lines.
* `-z/--search-zip`: Search compressed files (gzip, bzip2, lzma, xz, lz4,
  brotli, zstd). This is disabled by default.
* `-C/--context`: Show the lines surrounding a match.
* `--sort path`: Force ripgrep to sort its output by file name. (This disables
  parallelism, so it might be slower.)
* `-L/--follow`: Follow symbolic links while recursively searching.
* `-M/--max-columns`: Limit the length of lines printed by ripgrep.
* `--debug`: Shows ripgrep's debug output. This is useful for understanding
  why a particular file might be ignored from search, or what kinds of
  configuration ripgrep is loading from the environment.