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This article deals with TECO as it relates to esoteric programming. For more general information, see the Wikipedia article on TECO.

TECO is a 1963 language created for use in the text editor of the same name, designed for performing arbitrary edits to text. Due to limitations regarding the paper-tape that TECO programs were originally stored on when they were fed into computers, TECO syntax is terse and illegible. Almost every possible character is a command. TECO programs were used to perform replacements in program source code in order to correct mistakes, based on context rather than line numbers. Surprisingly, this was often more efficient than the alternatives available in its heyday. Programs were often written with exact specific input text in mind, and given their incomprehensible syntax it was joked that TECO enabled "Write-only Programming". In other words, TECO programs can be written, but afterwards cannot be read or understood.

TECO follows the imperative paradigm, with subprocedures being stored as text in variables.

The text editor TECO was the predecessor to Emacs, which used TECO internally before the adoption of Emacs Lisp; 'EMACS' refers to extensible TECO macros that originally comprised it.