Tilde

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The tilde is a grapheme which has several uses, described below. The name of the character comes from Spanish, from the Latin titulus meaning a title or superscription, and is pronounced "TILL-dee" or "TILL-duh" (SAMPA /"tIldI/ or /"tIld@/). It was originally written over a letter as a diacritic (see below), but has since acquired a number of other uses as a character in its own right. In this capacity (especially in lexicography) it is also sometimes known as the swung dash.

Contents

Diacritic use

In languages, tilde is a diacritic mark (~) placed over a letter to indicate a change in pronunciation, such as nasalisation.

In Portuguese, ã and õ represent nasalized a and o. In Estonian, õ is a separate letter, representing a separate vowel sound.

In Spanish, tilde over n (ñ) is a separate letter (called eñe) and is a palatal [n] (SAMPA J, IPA [ɲ]), pronounced like nh in Portuguese.

In Vietnamese, a tilde over a vowel represents a dipping (ngã) tone.

In the International Phonetic Alphabet (IPA), the tilde is used to mark nasalization and is placed above any phone that is nasalized.

The tilde was originally used as a form of contraction in Latin documents. When an n or m followed a vowel, it was often omitted, and a tilde placed over the preceding vowel to indicate the loss of the nasal. This is the origin of the use of tilde to indicate nasalization.

Logic

In logic, it is used as one way of representing negation: thus ~ p means "it is not the case that p".

Electronics

It can approximate the sine wave symbol (∿, U+223F), which is used in electronics to indicate alternating current, in place of +, −, or ⎓ for direct current. This most often appears on small transformers, which take household electrical current down to a low voltage suitable for small consumer electronics.

Punctuation

It is sometimes used as punctuation (instead of a hyphen or dash) between two numbers, to indicate that they are a range, rather than subtraction, or a hyphenated number (such as a part number or model number). Japanese and other Asian languages almost always use this convention, but it is often done for clarity in other languages as well. For example: 12~15 means "12 to 15", ~3 means "up to three" and 100~ means "100 and greater". In Japanese, the tilde is also used to separate a title and a subtitle in the same line.

Mathematics

In English, it is often used to mean "approximately". Therefore, ~10 would be "about 10". Similar symbols are used in mathematics, such as in π ≈ 3.14, "pi is about equal to 3.14". Since the double-tilde (≈) is not available from the keyboard, the tilde (~) became a subtitute when typing. There is also a triple-tilde (≋), which is used to show congruence.

Computing

In Unix shells, the tilde indicates the current user's home directory (e.g., /home/username). When prepended to a particular username, it indicates that user's home directory (e.g., ~janedoe means /home/janedoe). When some Unix shell commands overwrite a file, they can be made to keep a backup by renaming the original file as filename~.

Used in URLs on the World Wide Web, it often denotes a personal website on a Unix-based server. For example, http://www.widgets.com/~johndoe/ might be the personal web site of John Doe. This mimics the Unix shell usage of the tilde. However, when accessed from the web, file access is usually directed to a subdirectory in the user's home directory, such as /home/username/public_html or /home/username/www.

It is used in the Perl programming language as part of the pattern match operators for regular expressions:

$a =~ /regex/ returns true if the variable is matched.
$a !~ /regex/ returns false if the variable is matched.

The popularity of Perl's regular expression syntax has led to the use of these operators in other programming languages, such as Ruby.

The Emacs text editor forms the names used for backup files by appending a tilde to the original file name.

The tilde was part of Microsoft's name mangling scheme when it developed the VFAT filesystem. This upgrade introduced long filenames to Microsoft Windows, and permitted additional characters (such as the space) to be part of filenames, which were prohibited in previous versions. Programs written prior to this development could only access filenames in the so-called 8.3 format—the filenames consisted of a maximum of eight alphanumeric characters, followed by a period, followed by three more alphanumeric characters. In order to permit these legacy programs to access files in the VFAT filesystem, each file had to be given two names—one long, more descriptive one, and one that conformed to the 8.3 format. This was accomplished with a name-mangling scheme in which the first six characters of the filename are followed by a tilde and a digit. For example, "Program Files" becomes "PROGRA~1".

Computer hackers pronounce tilde either "squiggle" or "twiddle".

See History of the tilde for a history of how the tilde came to become part of the standard computer character sets.

Lexicography

In dictionaries, both bilingual and monolingual, tilde is usually referred to as swung dash. It is often used to replace the headword of an entry when it occurs within the entry, in order to save space. For example, ~ing would represent singing at the entry for sing.