The double less-than sign (<<) is used for an approximation of the much-less-than sign (≪). ASCII does not have much-less-than sign.

The double less-than sign (<<) is used for an approximation of the opening guillemet («). ASCII does not have guillemets.

In Bash, Perl, and Ruby, operator <<EOF (where "EOF" is an arbitrary string, but commonly "EOF" denoting "end of file") is used to denote the beginning of a here document.

In the C++ Standard Library, operator <<, when applied on an output stream, acts as insertion operator and performs an output operation on the stream.

Triple less-than sign[edit]

In PHP, operator <<<OUTPUT is used to denote the beginning of a heredoc statement (where OUTPUT is an arbitrary named variable.)

Less-than sign plus equals sign[edit]

The less-than sign plus the equals sign (<=) is used for an approximation of the less-than-or-equal-to sign (≤). ASCII does not have less-than-or-equal-to sign.

In BASIC, Lisp-family languages, and C-family languages (including Java and C++), operator <= means "less than or equal to".

In Fortran, operator .LE. means "less than or equal to".

In Bourne shell (and many other shells), less-than sign is used to redirect input from a file. Less-than plus ampersand (<&) is used to redirect from a file descriptor.

In HTML (and SGML and XML), the less-than sign is used at the beginning of tags. The less-than sign may be included with <. The less-than-or-equal-to sign may be included with ≤.