neo - Man Page

simulate the digital rain from "The Matrix"


neo [Options]...


neo recreates the digital rain effect from "The Matrix". Streams of random characters will endlessly scroll down your terminal screen. There are many differing depictions of this effect throughout the Matrix franchise. neo attempts to closely mimic the scene from "The Matrix" where Cypher explains the code to Neo. It imitates some of the finer details such as the characters used (half-width katakana), uneven colors, color palette, glitching, and flickering.

The digital rain is made of many "droplets". Each droplet scrolls vertically down a column. There can be multiple droplets in each column. Some characters on the screen are "glitched" - their values will change randomly until they are erased. The bottom of each droplet is a bit brighter than the rest.

You can run neo without any arguments, but it has many options to customize it to your liking. It can also respond to key presses (try pressing a number!), and it accepts a color file (see the "Color File" section below), which allows neo to display user-defined colors. neo will use Unicode characters by default if it detects a locale that supports UTF.


neo takes options in two forms: short and long. Short options cannot include an equal sign but long options can. Example for -S/--speed:

These will work:

These will not:

--S 16

-a,  --async

Makes each column of characters scroll at an independent speed. Each column's speed is still limited by the -S/--speed arg. All droplets in a column will always scroll at the speed.

-b,  --bold=NUM

Controls if and how neo displays bold characters. 0=off, 1=random (default), 2=all.

-C,  --colorfile=FILE

Read the colors from a file. This option is mutually exclusive with the -c/--color and --colormode=0 options. See the "Color File" section below for more info.

-c,  --color=COLOR

Sets the foreground text color. This option is mutually exclusive with the -C/--colorfile and --colormode=0 options. The available colors are: green, green2, green3, yellow, orange, red, blue, cyan, gold, rainbow, purple, pink, pink2, vaporwave, and gray.

-D,  --defaultbg

Use the default terminal background color. This option is mutually exclusive with the -C/--colorfile and --colormode=0 options.

-d,  --density=NUM

Controls how many droplets will appear onscreen. NUM is a decimal number. Its default value is 1.0. Values greater than 0.0 but less than 100.0 are allowed. However, values in the range [0.25, 4.0] will probably look best.

-F,  --fullwidth

Use two columns per character. This option is useful when displaying characters that take two columns to display such as Greek and full-width katakana.

-f,  --fps=NUM

Sets a frame rate target. By default, neo will run at 60Hz. neo does not attempt to query the OS for any display info. So it can't match your monitor's refresh rate by default unless it happens to be 60Hz. Lower frame rates will reduce CPU usage and improve battery life on portable devices.

-G,  --glitchpct=NUM

Sets the percentage of characters onscreen that glitch. NUM is a decimal number between 0.0 and 100.0 inclusive. The default value is 10.0 (i.e. 10%).

-g,  --glitchms=NUM1,NUM2

Controls how often the characters on screen glitch. A "glitch" refers to when a character changes into another. Each glitch is accompanied by a flickering of the character's color if colors are enabled. After each glitch, neo will wait for some time before doing the next glitch. The time it waits is chosen randomly to be between the two values provided (inclusive). NUM1 and NUM2 are positive integers that represent milliseconds. Their default values are 300 and 400.

-h,  --help

Shows the help message.

-l,  --lingerms=NUM1,NUM2

Controls how long characters stay onscreen after they finish scrolling. For each column, neo will pick a random value between NUM1 and NUM2 inclusive. NUM1 and NUM2 are positive integers that represent milliseconds. The default values are 1 and 3000.

-M,  --shadingmode=NUM

Controls how neo assigns color values to characters on the screen. 0=random (default), 1=gradient.

-m,  --message=STR

Displays a message in the center of the screen. The message is gradually uncovered as characters stream past it. This effect is similar to the title reveal in the movies. The message should be surrounded with double quotes. neo parses arguments using getopt_long(), which does not have Unicode support. So, unfortunately, this argument only accepts simple ASCII text. The message will not display well if you also use the -F/--fullwidth option. To unveil the message faster, the following options may help:

neo -m "the message" --speed=12 --density=3 --lingerms=1,1 --rippct=0

-p,  --profile

Turns on the profiling mode. This mode functions as normal except it times how long each frame takes and writes the values to a file called "time_profile.txt" in the current working directory.

-r,  --rippct=NUM

Sets the percentage of droplets that stop scrolling before reaching the bottom of the screen. NUM is a decimal number between 0.0 and 100.0 inclusive. The default value is 33.0 (i.e. about a third).

-S,  --speed=NUM

Controls how fast characters scroll down the screen. NUM is a decimal number that sets the number of characters drawn per second. The default value is 8.0. If -a/--async is used, this option sets an upper bound on the value chosen for each droplet's speed.

-s,  --screensaver

If this option is set, neo will exit on the first key press.

-V,  --version

Displays the version, build date, copyright, and license.


Tells neo to display Unicode characters between NUM1 and NUM2 inclusive. NUM1 and NUM2 are Unicode code points in hexadecimal (e.g. 0x1F030). This argument can be used multiple times. If --charset is not used, neo will only use the values provided by this option. If a charset is also specified, neo will use both the charset and the characters provided by this option.


Sets the charset that is used to draw characters onto the screen. It can be combined with the --chars option. The supported charsets are: ascii, extended, english, dec, decimal, digits, punc, bin, binary, hex, hexadecimal, katakana, greek, cyrillic, arabic, hebrew, devanagari, braille, and runic.


Sets the color mode. The accepted values are 0, 16, 32, and 256. 0 disables color (i.e. mono). 16 selects 16 colors. 32 selects 32-bit color. 256 selects 256 colors.


Sets the maximum number of droplets per column. The default value is 3.


Disables character glitching.


Sets the percentage of shortened droplets. If a droplet is not shortened, it will extend from the top of the screen to final line, which is often the bottom of the screen but not always (see also: -r/--rippct). NUM is a decimal number between 0.0 and 100.0 inclusive. The default value is 50.0 (i.e. 50%).


You can press keys while neo is running to control its behavior. The key bindings cannot be changed without modifying the program code. Some keys can be held to increase their effect (e.g. holding UP increases speed further).

Here are the available key controls:

´SPACE' - clears the screen
´UP' - increases the scrolling speed
´DOWN' - decreases the scrolling speed
´RIGHT' - increases the number of characters that are glitchy
´LEFT' - decreases the number of characters that are glitchy
´TAB' - toggles the shading mode between random and gradient
´ESC' - exits neo
´+' - increases the number of droplets onscreen
´-' - decreases the number of droplets onscreen
´a' - toggles asynchronous droplet speed
´p' - pauses neo
´q' - exits neo
´1' - sets the color to green
´2' - sets the color to green2
´3' - sets the color to green3
´4' - sets the color to gold
´5' - sets the color to pink2
´6' - sets the color to red
´7' - sets the color to blue
´8' - sets the color to cyan
´9' - sets the color to purple
´0' - sets the color to gray
´!' - sets the color to rainbow
´@' - sets the color to yellow
´#' - sets the color to orange
´$' - sets the color to pink
´%' - sets the color to vaporwave

Color File

neo can read a file that specifies the background color and all the foreground colors. The file is given via the -C/--colorfile option.

You can write comments using "//", "#", ";", "*", or "@". Comments can go on separate lines or after the data on any line. The first line that is not blank or a comment should be the version string. The version string line should look like:

neo_color_version N

where "N" is the color file version number, which is currently 1. The version string is optional, and if it is omitted, then neo will assume that the file adheres to the latest version's format. This could potentially break old color files. Ye have been warned! neo will try to maintain backwards compatability with older color file versions so long as their version is actually given.

Each data line in the file describes a color. The first line is the background color. Each subsequent line describes a foreground color. Each file must contain at least two lines: one for the background and one for the foreground. Typically, you will want to put the foreground colors in order of ascending brightness. neo will not sort the colors. The last color should usually be very bright (e.g. white).

Each data line in the file specifies one value or four values. If only one value is given, it is treated as a 16 or 256 terminal color code (e.g. 16 is black). If four values are given, the first is treated as a 16/256 color code and the other three are the RGB components of the 32-bit color. Each component is a value from 0 to 1000, which closely mimics how ncurses handles color. Each value is separated by a comma, and whitespace is allowed.

If more than one value is given on a line, then all four values must be given. Lines do not all have to have the same number of components i.e. some lines can just specify the 16/256 color code while others can specify all four values.

On most systems, if a value of "-1" is provided for the 16/256 color code, this will set the color to the system default. This can be useful if you want to keep the default background.

All ncurses implementations should allow you to override at least the first 256 colors, assuming your terminal supports it. Some will let you override even more than that. ncurses should restore all colors back to their previous state as long as neo exits cleanly.

If either of the 16 or 256 colormode options is used, all 32-bit RGB components in the color file will be parsed if they are given, but they will be unused.

Example 1: Blue text on a red background using only 256 color codes


Example 2: Different shades of purple text on a yellow background with some 32-bit color components


Example 3: Default background and various shades of green using only 256 color codes



neo can have two main performance issues: high CPU utilization and stuttering.  A terminal emulator with GPU acceleration (e.g. Alacritty) may significantly improve these issues. The CPU utilization by neo itself is fairly low, even at high frame rates on large screens. However, your terminal emulator may use substantial CPU resources to draw everything. Without a fast terminal emulator, this application may use up a whole CPU core or three.

Sometimes the text will not scroll smoothly. Again, a fast terminal emulator will probably help. You will also typically want the frame rate (i.e. --fps) to be evenly divisible by the character speed (i.e. -S/--speed). Sometimes, the glitching effect will lead to stuttering because a substantial number of characters onscreen will have to be redrawn. Reducing the glitchiness (i.e. --glitchpct) or disabling glitching (i.e. --noglitch) may help.

If you experience performance issues, here are some things to try:

1. Use a GPU-accelerated terminal emulator
2. Run neo on a smaller screen/window
3. Reduce the frame rate (e.g. --fps=30)
4. Reduce the number of droplets onscreen (e.g. -d 0.5)
5. Reduce the character speed (e.g. --speed=6)
6. Disabling glitching (i.e. --noglitch)
7. Disable colors (i.e. --colormode=0)
8. Disable bold characters (i.e. --bold=0)
9. Disable Unicode characters (i.e. --charset=ascii)

Here is a "potato mode" config that should perform well on most systems:


Example 0: Just run it


Example 1: Sets a faster, asynchronous scrolling speed with 256 colors

neo -S 12 -a --color=green3 --colormode=256

Example 2: Red text with a custom message and Cyrillic characters

neo --color=red --charset=cyrillic -m "IN SOVIET RUSSIA, COMPUTER PROGRAMS YOU!"

Example 3: Displays golden Greek characters that are full-width

neo --color=gold --charset=greek -F

Example 4: Uses --chars to draw Unicode dominoes

neo --chars=0x1F030,0x1F093 --fullwidth


Written by Stewart Reive

Reporting Bugs

Create an issue on GitHub:


This program is not affiliated with "The Matrix", Warner Bros. Entertainment Inc., Village Roadshow Pictures, Silver Pictures, nor any of their parent companies, subsidiaries, partners, or affiliates.

See Also

locale(1), localectl(1)


You get used to it. I... I don't even see the code. All I see is blonde, brunette, redhead. Hey! You uh... want a drink? :)


Feb 21 2022 neo version 0.6.1 neo User Manual