259 lines
9.8 KiB
Markdown
259 lines
9.8 KiB
Markdown
# Linux
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This document collects knowledge, tips and tricks on all things Linux, that don't get their own document.
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<!--toc:start-->
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- [Linux](#linux)
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- [Setup and Configuration](#setup-and-configuration)
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- [Locales and Keyboard Layouts](#locales-and-keyboard-layouts)
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- [configure layout 'US intl. with deadkeys'](#configure-layout-us-intl-with-deadkeys)
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- [Linux commands](#linux-commands)
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- [combine commands with *xargs*](#combine-commands-with-xargs)
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- [pipe output into clipboard](#pipe-output-into-clipboard)
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- [permissions](#permissions)
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- [octal permissions](#octal-permissions)
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- [Terminal](#terminal)
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- [ANSI escape sequences](#ansi-escape-sequences)
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- [Text Style](#text-style)
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- [Color codes](#color-codes)
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- [8-16 Colors](#8-16-colors)
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- [256 Colors](#256-colors)
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- [RGB Colors](#rgb-colors)
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<!--toc:end-->
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## Setup and Configuration
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### Locales and Keyboard Layouts
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Use `localectl` to display and configure locales and keyboard layout:
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```sh
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# show current locales
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localectl status
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```
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#### configure layout 'US intl. with deadkeys'
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To configure `US intl. with deadkeys`, set the following values:
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```sh
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X11 Layout: us
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X11 Model: default
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X11 Variant: intl
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```
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Use `localectl` to show the current settings.
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## Linux commands
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- [Linux commands](#linux-commands)
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- [combine commands with *xargs*](#combine-commands-with-xargs)
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### combine commands with *xargs*
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Some commands (e.g. `chmod`) can't handle input via pipe and require the input as arguments.
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`xargs` takes the standard input as list of arguments seperated by spaces or newlines and executes the given command with the input parsed to a list of arguments.
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Usage:
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```bash
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find . -type f | xargs chmod 644
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```
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### pipe output into clipboard
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> requires `xclip`
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One can save command output to the clipboard by piping it to `xclip`:
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```sh
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# usage
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command | xclip -selection clipboard
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# working example with 'echo'
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echo "hello world" | xclip -selection clipboard
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```
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> NOTE: the argument `-selection clipboard` is required
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## permissions
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Linux permissions are ordered as follows:
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- owner
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- group
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- others
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### octal permissions
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In octal representation the actions (read, write, execute) have the values:
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- read = 4
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- write = 2
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- execute = 1
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## Terminal
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- [ANSI escape sequences](#ansi-escape-sequences)
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### ANSI escape sequences
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Ansi escape sequences are used to format output in a terminal.
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They **are prefixed with an escape character**, which can be written in a few ways:
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- Ctrl-Key `^[`
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- Octal `\033` (\0 for octal)
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- Hexadecimal `\x1B` (\\x for hexadecimal)
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- Unicode `\u001b`
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The sequences is started with a `[` followed by the command and arguments.
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Arguments are separated with `;`.
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**Sequences are terminated with `m`.**
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``` bash
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# Example:
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\x1b[1;31m # Set style to bold, red foreground.
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```
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For the following tables we define `ESC = \x1B`
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#### Buffer Control
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| Sequence | Description |
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| :------- | :----------- |
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| `ESCc` | clear buffer |
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#### Cursor Control
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The following table lists codes to control the cursor:
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| Sequence | Description |
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| :--------------------- | :----------------------------------------------------- |
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| `ESC[H` | moves cursor to home position (0, 0) |
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| `ESC[<line>;<column>H` | moves cursor to `<line>`, `<column>` |
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| `ESC[<#>A` | moves cursor up # lines |
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| `ESC[<#>B` | moves cursor down # lines |
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| `ESC[<#>C` | moves cursor right by # columns |
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| `ESC[<#>D` | moves cursor left by # columns |
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| `ESC[<#>E` | moves cursor to beginning of next line, # lines down |
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| `ESC[<#>F` | moves cursor to beginning of previous line, # lines up |
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| `ESC[<#>G` | moves cursor to column # |
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| `ESC[6n` | request cursor position (reports as `ESC[#;#R`) |
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| `ESC M` | moves cursor one line up, scrolling if needed |
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| `ESC 7` | save cursor position (DEC) |
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| `ESC 8` | restores the cursor to the last saved position (DEC) |
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| `ESC[s` | save cursor position (SCO) |
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| `ESC[u` | restores the cursor to the last saved position (SCO) |
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#### Text Style
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| ESC Code Sequence | Reset Sequence | Description |
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| :---------------- | :------------- | :--------------------------------------------------------- |
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| `ESC[1;34;{...}m` | | Set graphics modes for cell, separated by semicolon (`;`). |
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| `ESC[0m` | | reset all modes (styles and colors) |
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| `ESC[1m` | `ESC[22m` | set bold mode. |
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| `ESC[2m` | `ESC[22m` | set dim/faint mode. |
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| `ESC[3m` | `ESC[23m` | set italic mode. |
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| `ESC[4m` | `ESC[24m` | set underline mode. |
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| `ESC[5m` | `ESC[25m` | set blinking mode |
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| `ESC[7m` | `ESC[27m` | set inverse/reverse mode |
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| `ESC[8m` | `ESC[28m` | set hidden/invisible mode |
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| `ESC[9m` | `ESC[29m` | set strikethrough mode. |
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> **Note:** Some terminals may not support some of the graphic mode sequences listed above.
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> **Note:** Both dim and bold modes are reset with the `ESC[22m` sequence.
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> The `ESC[21m` sequence is a non-specified sequence for double underline mode and only works in some terminals and is reset with `ESC[24m`.
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#### Color codes
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Most terminals support 8 and 16 colors, as well as 256 (8-bit) colors.
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These colors are set by the user, but have commonly defined meanings.
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##### 8-16 Colors
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| Color Name | Foreground Color Code | Background Color Code |
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| :--------- | :-------------------- | :-------------------- |
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| Black | `30` | `40` |
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| Red | `31` | `41` |
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| Green | `32` | `42` |
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| Yellow | `33` | `43` |
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| Blue | `34` | `44` |
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| Magenta | `35` | `45` |
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| Cyan | `36` | `46` |
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| White | `37` | `47` |
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| Default | `39` | `49` |
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| Reset | `0` | `0` |
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> **Note:** the _Reset_ color is the reset code that resets _all_ colors and text effects, Use _Default_ color to reset colors only.
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Most terminals, apart from the basic set of 8 colors, also support the "bright" or "bold" colors.
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These have their own set of codes, mirroring the normal colors, but with an additional `;1` in their codes:
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```sh
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# Set style to bold, red foreground.
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\x1b[1;31mHello
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# Set style to dimmed white foreground with red background.
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\x1b[2;37;41mWorld
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```
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Terminals that support the [aixterm specification](https://sites.ualberta.ca/dept/chemeng/AIX-43/share/man/info/C/a_doc_lib/cmds/aixcmds1/aixterm.htm) provides bright versions of the ISO colors, without the need to use the bold modifier:
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| Color Name | Foreground Color Code | Background Color Code |
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| :------------- | :-------------------- | :-------------------- |
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| Bright Black | `90` | `100` |
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| Bright Red | `91` | `101` |
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| Bright Green | `92` | `102` |
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| Bright Yellow | `93` | `103` |
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| Bright Blue | `94` | `104` |
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| Bright Magenta | `95` | `105` |
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| Bright Cyan | `96` | `106` |
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| Bright White | `97` | `107` |
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##### 256 Colors
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The following escape codes tells the terminal to use the given color ID:
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| ESC Code Sequence | Description |
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| :---------------- | :-------------------- |
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| `ESC[38;5;{ID}m` | Set foreground color. |
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| `ESC[48;5;{ID}m` | Set background color. |
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Where `{ID}` should be replaced with the color index from 0 to 255 of the following color table:
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The table starts with the original 16 colors (0-15).
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The proceeding 216 colors (16-231) or formed by a 3bpc RGB value offset by 16, packed into a single value.
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The final 24 colors (232-255) are grayscale starting from a shade slighly lighter than black, ranging up to shade slightly darker than white.
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Some emulators interpret these steps as linear increments (`256 / 24`) on all three channels, although some emulators may explicitly define these values.
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##### RGB Colors
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More modern terminals supports [Truecolor](https://en.wikipedia.org/wiki/Color_depth#True_color_.2824-bit.29) (24-bit RGB), which allows you to set foreground and background colors using RGB.
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These escape sequences are usually not well documented.
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| ESC Code Sequence | Description |
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| :---------------------- | :--------------------------- |
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| `ESC[38;2;{r};{g};{b}m` | Set foreground color as RGB. |
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| `ESC[48;2;{r};{g};{b}m` | Set background color as RGB. |
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> Note that `38` and `48` corresponds to the 16 color sequence and is interpreted by the terminal to set the foreground and background color respectively.
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> Where as `;2` and `;5` sets the color format.
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