{"history":[],"article":{"id":"5a413047-00dd-403b-b7ca-3a1ebc08ebeb","title":"Here document","slug":"here-document","content":":::summary\n:::\n\n# \nIn [computing](https://bliptext.com/articles/computing), a **here document** (**here-document**, **here-text**, **heredoc**, **hereis**, **here-string** or **here-script**) is a [file](https://bliptext.com/articles/computer-file) [literal](https://bliptext.com/articles/literal-computer-programming) or [input stream](https://bliptext.com/articles/input-stream) [literal](https://bliptext.com/articles/literal-computer-programming): it is a section of a [source code](https://bliptext.com/articles/source-code) [file](https://bliptext.com/articles/computer-file) that is treated as if it were a separate [file](https://bliptext.com/articles/computer-file).\nThe term is also used for a form of multiline [string literals](https://bliptext.com/articles/string-literal) that use similar syntax, preserving line breaks and other whitespace (including indentation) in the text.\nHere documents originate in the [Unix shell](https://bliptext.com/articles/unix-shell), and are found in the [Bourne shell](https://bliptext.com/articles/bourne-shell) since 1979, and most subsequent shells.\nHere document-style string literals are found in various [high-level languages](https://bliptext.com/articles/high-level-language), notably the [Perl programming language](https://bliptext.com/articles/perl) (syntax inspired by Unix shell) and languages influenced by Perl, such as [PHP](https://bliptext.com/articles/php) and [Ruby](https://bliptext.com/articles/ruby-programming-language).\n[JavaScript](https://bliptext.com/articles/javascript) also supports this functionality via [template literals](https://bliptext.com/articles/string-interpolation), a feature added in its 6th revision ([ES6](https://bliptext.com/articles/ecmascript)).\nOther high-level languages such as [Python](https://bliptext.com/articles/python-programming-language), [Julia](https://bliptext.com/articles/julia-programming-language) and [Tcl](https://bliptext.com/articles/tcl) have other facilities for multiline strings.\nHere documents can be treated either as files or strings.\nSome shells treat them as a [format string](https://bliptext.com/articles/format-string) literal, allowing [variable substitution](https://bliptext.com/articles/variable-programming) and [command substitution](https://bliptext.com/articles/command-substitution) inside the literal.\n\n# Overview\nThe most common syntax for here documents, originating in Unix shells, is followed by a [delimiting](https://bliptext.com/articles/delimiter) [identifier](https://bliptext.com/articles/identifier) (often the word or ), followed, starting on the next line, by the text to be quoted, and then closed by the same [delimiting](https://bliptext.com/articles/delimiter) [identifier](https://bliptext.com/articles/identifier) on its own line.\nThis syntax is because here documents are formally stream literals, and the content of the here document is often redirected to [stdin](https://bliptext.com/articles/stdin) (standard input) of the preceding command or current shell script/executable.\nThe here document syntax is analogous to the shell syntax for input [redirection](https://bliptext.com/articles/redirection-computing), which is followed by the name of the file to be used as input.\nOther languages often use substantially similar syntax, but details of syntax and actual functionality can vary significantly.\nWhen used simply for string literals, the does not indicate indirection, but is simply a starting delimiter convention.\nIn some languages, such as Ruby, is also used for input redirection, thus resulting in being used twice if one wishes to redirect from a here document string literal.\n\n# File literals\nNarrowly speaking, here documents are file literals or stream literals.\nThese originate in the Unix shell, though similar facilities are available in some other languages.\n\n## Unix shells\nHere documents are available in many Unix shells.\nIn[ ](https://bliptext.com/articles/tr-unix)the[ ](https://bliptext.com/articles/tr-unix)following[ ](https://bliptext.com/articles/tr-unix)example,[ ](https://bliptext.com/articles/tr-unix)text[ ](https://bliptext.com/articles/tr-unix)is[ ](https://bliptext.com/articles/tr-unix)passed[ ](https://bliptext.com/articles/tr-unix)to[ ](https://bliptext.com/articles/tr-unix)the[ ](https://bliptext.com/articles/tr-unix)[ ](https://bliptext.com/articles/tr-unix)command[ ](https://bliptext.com/articles/tr-unix)(transliterating[ ](https://bliptext.com/articles/tr-unix)lower[ ](https://bliptext.com/articles/tr-unix)to[ ](https://bliptext.com/articles/tr-unix)upper-case)[ ](https://bliptext.com/articles/tr-unix)using[ ](https://bliptext.com/articles/tr-unix)a[ ](https://bliptext.com/articles/tr-unix)here[ ](https://bliptext.com/articles/tr-unix)document.\nThis could be in a shell file, or entered interactively at a prompt.\nIn this case was used as the delimiting identifier.\nIt specified the start and end of the here document.\nThe redirect and the delimiting identifier do not need to be separated by a space: < {} or []).\n\n## OS/JCL\nOn IBM's [Job Control Language](https://bliptext.com/articles/job-control-language) (JCL) used on its earlier [MVS](https://bliptext.com/articles/mvs) and current [z/OS](https://bliptext.com/articles/z-os) operating systems, data which is inline to a job stream can be identified by an * on a DD statement, such as //SYSIN DD *\nor\n//SYSIN DD *,DLM=text\nIn the first case, the lines of text follow and are combined into a pseudo file with the DD name SYSIN.\nAll records following the command are combined until either another OS/JCL command occurs (any line beginning with //), the default [EOF](https://bliptext.com/articles/end-of-file) sequence (/*) is found, or the physical end of data occurs.\nIn the second case, the conditions are the same, except the DLM= operand is used to specify the text string signalling end of data, which can be used if a data stream contains JCL (again, any line beginning with //), or the /* sequence (such as comments in C or C++ source code).\nThe following compiles and executes an assembly language program, supplied as in-line data to the assembler.\nThe //SYSIN DD * statement is the functional equivalent of <

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