What is special character in linux

Ubuntu Documentation

You can enter and view thousands of characters from most of the world’s writing systems, even those not found on your keyboard. This page lists some different ways you can enter special characters.

Methods to enter characters

Characters

The character map application allows you to find and insert unusual characters, including emoji, by browsing character categories or searching for keywords.

You can launch Characters from the Activities overview.

Compose key

A compose key is a special key that allows you to press multiple keys in a row to get a special character. For example, to type the accented letter Г© , you can press compose then ‘ then e .

Keyboards don’t have specific compose keys. Instead, you can define one of the existing keys on your keyboard as a compose key.

You need to have Tweaks installed on your computer to change this setting.

Define a compose key

Open the Activities overview and start typing Tweaks .

Click Tweaks to open the application.

Click the Keyboard & Mouse tab.

Click Disabled next to the Compose Key setting.

Turn the switch on in the dialog and pick the keyboard shortcut you want to use.

Tick the checkbox of the key that you want to set as the Compose key.

Close the dialog.

Close the Tweaks window.

You can type many common characters using the compose key, for example:

Press compose then ‘ then a letter to place an acute accent over that letter, such as Г© .

Press compose then ` (back tick) then a letter to place a grave accent over that letter, such as ГЁ .

Press compose then » then a letter to place an umlaut over that letter, such as Г« .

Press compose then — then a letter to place a macron over that letter, such as Д“ .

For more compose key sequences, see the compose key page on Wikipedia .

Code points

You can enter any Unicode character using only your keyboard with the numeric code point of the character. Every character is identified by a four-character code point. To find the code point for a character, look it up in the Characters application. The code point is the four characters after U+ .

To enter a character by its code point, press Ctrl + Shift + U , then type the four-character code and press Space or Enter . If you often use characters that you can’t easily access with other methods, you might find it useful to memorize the code point for those characters so you can enter them quickly.

Keyboard layouts

You can make your keyboard behave like the keyboard for another language, regardless of the letters printed on the keys. You can even easily switch between different keyboard layouts using an icon in the top bar. To learn how, see Use alternative keyboard layouts .

Input methods

An Input Method expands the previous methods by allowing to enter characters not only with keyboard but also any input devices. For instance you could enter characters with a mouse using a gesture method, or enter Japanese characters using a Latin keyboard.

To choose an input method, right-click over a text widget, and in the menu Input Method , choose an input method you want to use. There is no default input method provided, so refer to the input methods documentation to see how to use them.

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Linux Special and Escape Characters in FileName

In Linux, whitespace is a special character and one of the most frequently used characters. It separates the commands or arguments to the commands. For example, the copy command treats the first file assigned to it as the source file and the second file as the destination file.

These two file arguments are separated by whitespace. So if the file name contains whitespace, it creates a problem on the command line. This tutorial we discuss how you can create files with special characters and how to use them on the command line effectively.

Handling special characters

Let us try to create a file with spaces in its name with touch command.

The ls command in the above output shows that we do not get a single file but three files, i.e. file, spaces and with. This is because touch command considers the name as three different files, and not as a single file.

Two methods are available for handling these characters that have special meaning for shell. First, one is using quotes and second is with escape character.

Quotes

The simplest method is using quotes with the file name. Now, let us try creating the above file with quotes.

Now, you can see the file named «file with spaces». Both single quotes and double quotes can be used with file names, but it is advised to use single quotes. This is because some special characters cannot be escaped by double quotes. Single quotes handle them as well. Other special characters like $, *, ? etc can also be used in file names.

Another example

In the above example quotes are more important. Because * is a shell wildcard that matches any character, you will be in trouble if you don’t use the quotes. Without the quotes, the shell removes File*.txt as intended, but in addition File.txt, File2.txt, File22.txt and others will get deleted.

Escaping characters

This is another method that can be used for files with special characters in their names. The backslash character escapes the character following it. It means that the character that immediately follows backslash character is treated as normal character by the shell and not as special character.

For example, we can use backslash for creating a file that contains spaces in its name.

Similarly, the other special characters can also be escaped with backslash:

Now, you have seen that the quotes (single or double) and the backslash characters are the special characters that are used for handling special characters. So how can you use these characters in your file names? For quotes, you can use backslash:

That was simple. So what about backslash? Remember, backslash escapes every special character immediately following it? So we use backslash for escaping backslash itself.

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What are special characters in Linux?

How do I use special characters in Linux?

On Linux, one of three methods should work: Hold Ctrl + ⇧ Shift and type U followed by up to eight hex digits (on main keyboard or numpad). Then release Ctrl + ⇧ Shift .

What are special characters in Unix?

5. Basic Unix : special characters

• single quotes.
• double quotes.
• backslash characters.
• pound characters.
• cat : display a text file in the terminal window.
• gedit : a graphical editor.
• 3dDeconvolve -help.

What is a special character?

: a symbol used in writing, typing, etc., that represents something other than a letter or number.

What is the meaning of special character in bash?

Special characters. Some characters are evaluated by Bash to have a non-literal meaning. Instead, these characters carry out a special instruction, or have an alternate meaning; they are called “special characters”, or “meta-characters”.

How do you write special characters?

Ensure that the Num Lock key has been pressed, to activate the numeric key section of the keyboard. Press the Alt key, and hold it down. While the Alt key is pressed, type the sequence of numbers (on the numeric keypad) from the Alt code in the above table.

What are all the special characters?

Password Special Characters

Character	Name	Unicode
Space	U+0020
!	Exclamation	U+0021
”	Double quote	U+0022
#	Number sign (hash)	U+0023

How do I remove special characters in Unix?

Remove CTRL-M characters from a file in UNIX

1. The easiest way is probably to use the stream editor sed to remove the ^M characters. Type this command: % sed -e “s/^M//” filename > newfilename. …
2. You can also do it in vi: % vi filename. Inside vi [in ESC mode] type: :%s/^M//g. …
3. You can also do it inside Emacs. To do so, follow these steps:

What is $$ in bash?

$$ is the pid (process id) of the shell interpreter running your script. … It’s the process ID of the bash process. No concurrent processes will ever have the same PID.

Why is used in Unix?

Unix is an operating system. It supports multitasking and multi-user functionality. Unix is most widely used in all forms of computing systems such as desktop, laptop, and servers. On Unix, there is a Graphical user interface similar to windows that support easy navigation and support environment.

What’s a special character example?

A special character is a character that is not an alphabetic or numeric character. Punctuation marks and other symbols are examples of special characters. … For example, when creating a web page with HTML, the quote (“) symbol is used to store attribute values.

How many special characters are there?

The 33 characters classified as ASCII Punctuation & Symbols are also sometimes referred to as ASCII special characters. See § Latin-1 Supplement and § Unicode symbols for additional “special characters”.

Is a number a special character?

A special character is one that is not considered a number or letter. Symbols, accent marks, and punctuation marks are considered special characters. Similarly, ASCII control characters and formatting characters like paragraph marks are also special characters.

What is bash symbol?

Special bash characters and their meaning

Special bash character	Meaning
#	# is used to comment a single line in bash script
$$	$$ is used to reference process id of any command or bash script
$0	$0 is used to get the name of the command in a bash script.
$name	$name will print the value of variable “name” defined in the script.

What does $1 do in bash?

$1 is the first command-line argument passed to the shell script. … $0 is the name of the script itself (script.sh) $1 is the first argument (filename1) $2 is the second argument (dir1)

What is shell command?

A shell is a computer program that presents a command line interface which allows you to control your computer using commands entered with a keyboard instead of controlling graphical user interfaces (GUIs) with a mouse/keyboard combination. … The shell makes your work less error-prone.

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What are character special and block special files in a unix system? [duplicate]

How are character special files and block special files different from regular files in a Unix-like system? Why are they called “character special” and “block special” respectively?

3 Answers 3

When a program reads or writes data from a file, the requests go to a kernel driver. If the file is a regular file, the data is handled by a filesystem driver and it is typically stored in zones on a disk or other storage media, and the data that is read from a file is what was previously written in that place. There are other file types for which different things happen.

When data is read or written to a device file, the request is handled by the driver for that device. Each device file has an associated number which identifies the driver to use. What the device does with the data is its own business.

Block devices (also called block special files) usually behave a lot like ordinary files: they are an array of bytes, and the value that is read at a given location is the value that was last written there. Data from block device can be cached in memory and read back from cache; writes can be buffered. Block devices are normally seekable (i.e. there is a notion of position inside the file which the application can change). The name “block device” comes from the fact that the corresponding hardware typically reads and writes a whole block at a time (e.g. a sector on a hard disk).

Character devices (also called character special files) behave like pipes, serial ports, etc. Writing or reading to them is an immediate action. What the driver does with the data is its own business. Writing a byte to a character device might cause it to be displayed on screen, output on a serial port, converted into a sound, . Reading a byte from a device might cause the serial port to wait for input, might return a random byte ( /dev/urandom ), . The name “character device” comes from the fact that each character is handled individually.

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Allowed characters in Linux environment variable names

What characters are allowed in Linux environment variable names? My cursory search of man pages and the web did only produce information about how to work with variables, but not which names are allowed.

I have a Java program that requires an defined environment variable containing a dot, like com.example.fancyproperty . With Windows I can set that variable, but I had no luck setting it in linux (tried in SuSE and Ubuntu). Is that variable name even allowed?

7 Answers 7

These strings have the form name=value; names shall not contain the character ‘=’. For values to be portable across systems conforming to IEEE Std 1003.1-2001, the value shall be composed of characters from the portable character set (except NUL and as indicated below).

So names may contain any character except = and NUL, but:

Environment variable names used by the utilities in the Shell and Utilities volume of IEEE Std 1003.1-2001 consist solely of uppercase letters, digits, and the ‘_’ (underscore) from the characters defined in Portable Character Set and do not begin with a digit. Other characters may be permitted by an implementation; applications shall tolerate the presence of such names.

So while the names may be valid, your shell might not support anything besides letters, numbers, and underscores.

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