[adrian_b]

The character "|" has been introduced in computers in the language NPL at IBM in December 1964 as a notation for bitwise OR, replacing ".OR.", which had been used by IBM in its previous programming language, "FORTRAN IV" (OR was between dots to distinguish it from identifiers, marking it as an operator).

The next year the experimental NPL (New Programming Language) has been rebranded as PL/I and it has become a commercial product of IBM.

Following PL/I, other programming languages have begun to use "&" and "|" for AND and OR, including the B language, the predecessor of C.

The pipe and its notation have been introduced in the Third Edition of UNIX (based on a proposal made by M. D. McIlroy), in 1972, so after the language B had been used for a few years and before the development of C. The oldest documentation about pipes that I have seen is in "UNIX Programmer's Manual Third Edition" from February 1973.

Before NPL, the vertical bar had already been used in the Backus-Naur notation introduced in the report about ALGOL 60 as a separator between alternatives in the description of the grammar of the language, so with a meaning somewhat similar to OR.

[hollerith]

>as a notation for bitwise OR, replacing ".OR.", which had been used by IBM in its previous programming language, "FORTRAN IV".

Untrue: ".OR." in FORTRAN meant ordinary OR, not bitwise OR. I don't remember ever seeing bitwise OR or AND or XOR in FORTRAN IV.

[adrian_b]

That is right, but I did not want to provide too many details that did not belong to the topic.

FORTRAN IV did not have bit strings, it had only Boolean values ("LOGICAL").

Therefore all the logical operators could be applied only to Boolean operands, giving a Boolean result.

The same was true for all earlier high-level programming languages.

The language NPL, renamed PL/I in 1965, has been the first high-level programming language that has introduced bit string values, so the AND, OR and NOT operators could operate on bit strings, not only on single Boolean values.

If PL/I would have remained restricted to the smaller character set accepted by FORTRAN IV in source texts, they would have retained the FORTRAN IV operators ".NOT.", ".AND.", ".OR.", extending their meaning as bit string operators.

However IBM has decided to extend the character set, which has allowed the use of dedicated symbols for the logical operators and also for other operators that previously had to use keywords, like the relational operators, and also for new operators introduced by PL/I, like the concatenation operator.