Backslash

[6][a] In June 1960, IBM published an "Extended character set standard" that includes the symbol at 0x19.

The Committee adopted these changes into the draft American Standard (subsequently called ASCII) at its November 1961 meeting.

[4] These operators were used for min and max in early versions of the C programming language supplied with Unix V6[7] and V7.

Regular expression languages used it the same way, changing subsequent literal characters into metacharacters and vice versa.

[12] In APL \ is called Expand when used to insert fill elements into arrays, and Scan when used to produce prefix reduction (cumulative fold).

[14] MS-DOS 2.0, released 1983, copied the idea of a hierarchical file system from Unix and thus used the (forward) slash as the directory separator.

[15] Possibly on the insistence of IBM,[16][17] Microsoft added the backslash to allow paths to be typed at the command line interpreter prompt, while retaining compatibility with MS-DOS 1.0 (in which / was the command-line option indicator.

[20][21] The backslash is used in the TeX typesetting system and in RTF files to begin markup tags.

Due to extensive use of the 005C code point to represent the yen sign, even today some fonts such as MS Mincho render the backslash character as a ¥, so the characters at Unicode code points 00A5 (¥) and 005C (\) both render as ¥ when these fonts are selected.

Computer programs still treat 005C as a backslash in these environments but display it as a yen sign, causing confusion, especially in MS-DOS filenames.

[28] Several other ISO 646 versions also replace backslash with other characters, including ₩ (Korean), Ö (German, Swedish), Ø (Danish, Norwegian), ç (French) and Ñ (Spanish), leading to similar problems, though with less lasting impact compared to the yen sign.