Forward Slash Definition

A forward slash is an upward-to-the-right sloping straight line character that has several important applications in a computer context.

In Linux and other Unix-like operating systems, a forward slash is used to represent the root directory, which is the directory that is at the top of the directory hierarchy and that contains all other directories and files on the system. Thus every absolute path, which is the address of a filesystem object (e.g., file or directory) relative to the root directory, begins with a forward slash.

Forward slashes are also used as separators for filesystem objects in both absolute paths and relative paths. A relative path is the location of a filesystem object relative to the current directory (i.e., the directory in which a user is currently working). A forward slash is also used following the final item in either type of path to indicate that that item is a directory. Thus, for example, in the absolute path /home/roberto/sales/, the first slash represents the root directory, the second and third slashes separate directories, and the final slash indicates that sales is a directory rather than a file.

This contrasts with paths in MS-DOS and similar operating systems (such as FreeDOS) and the Microsoft Windows operating systems, in which directories and files are separated with backslashes. The backslash is an upward-to-the-left sloping straight line character that is a mirror image of the forward slash. A backslash is not used to represent the root directory in such operating systems because, in contrast to Unix-like systems, there is no single root directory; rather, a separate letter of the alphabet is used for each root directory.

Forward slashes are used in such operating systems, but their role is to indicate a switch (i.e., an option) for a command. In Unix-like operating systems, in contrast, options are indicated by hyphens: a single hyphen for a single-letter option and two consecutive hyphens for a single-word or multiple-word option.

Forward slashes are also used in URLs (universal resource locators) to separate directories and files, because URLs are based on the UNIX directory structure. A major difference from the UNIX usage is that they begin with a scheme (e.g., http or ftp) rather than a root directory represented by a forward slash and that the scheme is followed directly by the sequence of a colon and two consecutive forward slashes to indicate the start of the directories and file portion of the URL.

Another use of forward slashes is to indicate comments in some programming languages. A comment is a statement that is included in source code for the purpose of reminding the developer or notifying others about some aspect of the code but which is ignored by compilers. Source code is the original version of a program as written by a human in plain text and before being compiled into a ready-to-run form. For example, comments in C, C++ and Java as well as CSS (cascading style sheets) begin with a forward slash and an asterisk and end with the same characters in the opposite order. C++ and Java as well as newer versions of C also allow single-line comments that begin with two consecutive slashes and do not require any closing tag.

Forward slashes are also used in HTML (hypertext markup language) and related markup languages, including XHTML (extensible HTML) and XML (extensible markup language). In such languages, a slash is used in each closing tag to indicate that it is a closing tag as well as in tags that do not require closing tags. Examples in HTML include </b>, which ends a section of bold text that had been started with the tag <b>, and <br />, which is used to indicate the start of a new line of text and does not require a closing tag.

In addition, forward slashes are used in regular expressions. Regular expressions are a system of using certain strings (i.e., sequences of characters) according to specified syntax rules to match desired words, phrases, etc. and thus perform search, replace and other text manipulation operations. They are utilized by many text editors and are supported by many programming languages.

Forward slashes also have a several uses that are not specific to computers. One is as a division symbol on keyboards and in programming. Another is to indicate a connection between words in place of a hyphen. Forward slashes are also commonly used as delimiters in dates.

Created June 25, 2006.
Copyright © 2006 The Linux Information Project. All Rights Reserved.