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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 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

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

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. 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).
    2. .ignore globs, which take precedence over all gitignore globs when there's a conflict.
    3. .rgignore globs, which take precedence over all .ignore globs when there's a conflict.
  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.)

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 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 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 0th 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 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. 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. 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 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.