1. Introduction

In this tutorial, we will learn how to use the fzf command to perform fuzzy searches in texts, lists of files, among others. We’ll also explore some basic and advanced applications of the fzf utility to increase our productivity.

2. About fzf

A fuzzy search works by applying an approximate string matching technique rather than an exact match. The results are then ordered by their ranking score.

fzf is an interactive command-line filter that reads lines from stdin, filters the lines using fuzzy search, and forwards the filtered lines to stdout. It supports both script and interactive modes. In the interactive mode, fzf provides an interface to read search parameters and filters the input on-the-go.

fzf works in a different way than grep and find, as it performs fuzzy searches rather than regex or glob searches.

3. Installation

We can find fzf in most package repositories. On a Debian-based distribution, we can install fzf using apt:

$ sudo apt install fzf

To install it from the source, refer to fzf on GitHub.

4. Basic Usage

Usually,  fzf is piped from the stdout of another program, such as ps, or apt-cache search. When fzf is not piped, it invokes find to recursively list all non-hidden files under the current directory and begins the search on the list of file names:

$ fzf

The program interface starts in fullscreen mode by default, and the search begins at the bottom. We can change the behavior using arguments:

--reverse 
        Display from the top of the screen 
--height N% 
        Use only N% height instead of full screen. 
--query PARAM 
        Begin search with PARAM as the initial query 
--multi 
        Enable multi-select with tab/shift-tab. 
-f, --filter PARAM
        Show matches for PARAM without the interactive finder

To start the fzf finder at 50% height and display files ending with .md:

$ fzf --reverse --multi --height 50% --query=.md$

To run fzf in script mode and disable the interactive finder:

$ fzf -f .md$

We can find all the available options in the man page.

4.1. Shell Key Bindings

During installation, fzf enables three key bindings to the shell:

  1. CTRL-R: search on recent history based on $HISTFILE, then return selected entry to the terminal
  2. CTRL-T: recursively search for a filename under $PWD, then return selected entries to the terminal
  3. ALT-C: recursively search for a directory name under $PWD, then cd into the selected entry

4.2. Filename Autocomplete

In the terminal, we can trigger fzf to autocomplete filenames by typing ** and then the TAB key after the term to find:

$ ls /etc/sorce**<TAB>
> source                                      
  64/3158                                     
> /etc/apt/sources.list                       
  /etc/apt/sources.list.d                     
  /etc/apt/sources.list.save

Notice that the argument to ls is incorrect at first but fzf returns the correct file paths.

4.3. Kill Command Autocomplete

With kill and fzf, we can easily select processes to send signals to. After kill -SIGNAL, hit the TAB key to bring the fzf process finder, then select the desired processes to autocomplete the pid values:

$ kill -18 <TAB>
> gedit<ENTER>                                                
  55/295                                               
> user     8841     1  0 09:03 ?        00:00:01 gedit
$ kill -18 8841

4.4. Using Different Search Modes

fzf supports multiple search modes. To review how fzf operates in each mode, let’s create a plaintext file:

$ tee /tmp/fzf.in <<EOF
I mean to confound these bungers
I swallowed a bug
Was that the Primary Buffer Panel?
Captain Reynolds
EOF

fzf searches in fuzzy mode by default. When we search for the word “bug”, the degree of match is higher in the 2nd line of the heredoc than on the 1st line, and there is no match for the 3rd and 4th lines:

$ cat /tmp/fzf.in | fzf -f bug
I swallowed a bug
I mean to confound these bungers

Instead of fuzzy mode, we can prefix the keyword with an apostrophe to match in exact mode:

$ cat /tmp/fzf.in | fzf -f \'bug 
$ #cat /tmp/fzf.in | fzf -f "'bug"
I swallowed a bug

Lines 1 and 2 are equivalent. All characters which have special meaning in the shell must be escaped if not enclosed in quotes.

Negation mode matches a keyword in exact mode and filters out matching lines. We can prefix the keyword with ! for negation:

$ cat /tmp/fzf.in | fzf -f  \!bug
I mean to confound these bungers
Was that the Primary Buffer Panel?
Captain Reynolds

We can also specify if a substring appears at the beginning or at the end using ^ and $ respectively. This is called an anchored match:

$ cat /tmp/fzf.in | fzf -f s$
Captain Reynolds
I mean to confound these bungers
$ cat /tmp/fzf.in | fzf -f \^c
Captain Reynolds

We can combine multiple filters separated by a space. A pipe separator acts as the OR operator. The following command filters all lines that begin with “I” and that match either “man” or “ban” in fuzzy mode.

$ cat /tmp/fzf.in | fzf -f "^i ban | man"
I mean to confound these bungers

Note that we can use the +i flag to enable case sensitive match.

5. Example of Applications

Since fzf excels by providing an interactive interface, we can use it as a browser in different scenarios, and use its fuzzy search capability to narrow down the searches with a high error tolerance.

The preview option displays the output of the specified command in a preview pane for the selected line.

In a command embedded within the preview flag, the expression {} expands to the whole line, whereas {1} expands to the 1st column of the current line, {2} expands to the 2nd column, and so on. {n} expands the zero-based index of the line:

$ cat /tmp/fzf.in | fzf --preview 'echo line# {n}. first word: {1}. total words: `wc -w <<< {}`'

Let’s view the threads of a process interactively by embedding our ps command in the –preview flag:

$ ps axo pid,rss,comm --no-headers | fzf --preview 'ps o args {1}; ps mu {1}'

Similarly, we can browse package dependencies, for example, in a Debian based Linux:

$ apt-cache search . | fzf --preview 'apt-cache depends {1}' 

We can also browse through the git commit history and view minimal information about each commit:

$ git log --oneline | fzf --preview 'git show --name-only {1}'

A vim plugin for fzf is also available. An extensive list of advanced applications can be found on the official wiki page.

6. Conclusion

In this tutorial, we’ve learned what fuzzy searches are and how we can do them using fzf. We also explored how we can use fzf along with other command-line tools to better filter and visualize their output.

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