Backquote

Backquote, also called grave accent, refers to the character ` (ASCII 96). It is distinct from the apostrophe or quotation marks and is produced by the grave key on many keyboards, typically located to the left of the 1 key and shared with the tilde (~).

In typography and linguistics, the grave accent is a diacritic placed over vowels in various writing systems to indicate a specific pronunciation or tone. It is used in many languages on letters such as à, è, and ù, and in some linguistic transcriptions to denote phonetic features.

In computing, backquotes are employed for command substitution in several shells. Historically, text between backquotes is executed by the shell, and the command’s output replaces the backquoted section. For example, echo The date is `date`. Many modern shells prefer the $(command) form for readability and to allow nesting, but backquotes remain supported in many environments. Backquotes may also be escaped to appear literally.

Additional uses appear in programming languages and databases. In MySQL, backticks quote identifiers, enabling the use of reserved words or special characters as names. In R, backticks allow using non-standard identifiers (such as names with spaces). In Julia, backticks create a shell command that can be executed with run; for example, run(`ls -l`). In Python 2, a backtick operator performed the repr function (x`y`), a feature removed in Python 3. In markup languages like Markdown, backticks denote inline code spans, and triple backticks denote fenced code blocks.

Overall, the backquote functions as a versatile symbol across typography, shell scripting, programming, and markup, with its specific meaning highly context-dependent.