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.