## 10.2.1 I/O Control List

The I/O control list specifies one or more of the following:

- The I/O unit to act upon ([UNIT=]io-unit)

  This specifier must be present; the rest are optional.

- The format (explicit or list-directed) to use for data editing; if explicit, the keyword form must appear ([FMT=]format)
- The namelist group name to act upon ([NML=]group)
- The number of a record to access (REC)
- The name of a variable that contains the completion status of an I/O operation (IOSTAT)
- The label of the statement that receives control if an error (ERR), end-of-file (END), or end-of-record (EOR) condition occurs
- The key field (KEY[con]) and key of reference (KEYID) to access a keyed-access record (VMS only)
- Whether you want to use advancing or nonadvancing I/O (ADVANCE)
- The number of characters read from a record (SIZE) by a nonadvancing READ statement

No control specifier can appear more than once, and the list must not contain both a format specifier and namelist group name specifier.

Control specifiers can take any of the following forms:

- Keyword form

  When the keyword form (for example, UNIT=io-unit) is used for all control-list specifiers in an I/O statement, the specifiers can appear in any order.

- Nonkeyword form

  When the nonkeyword form (for example, io-unit) is used for all control-list specifiers in an I/O statement, the io-unit specifier must be the first item in the control list. If a format specifier or namelist group name specifier is used, it must immediately follow the io-unit specifier.

- Mixed form

  When a mix of keyword and nonkeyword forms is used for control-list specifiers in an I/O statement, the nonkeyword values must appear first. Once a keyword form of a specifier is used, all specifiers to the right must also be keyword forms.

The following sections describe the control-list specifiers in detail.

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