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RedHat 9 (Linux i386) - man page for scan (redhat section n)

scan(n) 			      Tcl Built-In Commands				  scan(n)

_________________________________________________________________________________________________

NAME
       scan - Parse string using conversion specifiers in the style of sscanf

SYNOPSIS
       scan string format ?varName varName ...?
_________________________________________________________________

INTRODUCTION
       This  command  parses fields from an input string in the same fashion as the ANSI C sscanf
       procedure and returns a count of the number of conversions performed, or -1 if the end  of
       the  input string is reached before any conversions have been performed.  String gives the
       input to be parsed and format indicates how to parse it, using % conversion specifiers  as
       in sscanf.  Each varName gives the name of a variable; when a field is scanned from string
       the result is converted back into a string and assigned to the corresponding variable.  If |
       no  varName  variables  are  specified, then scan works in an inline manner, returning the |
       data that would otherwise be stored in the variables as a list.	In the	inline	case,  an |
       empty  string  is  returned when the end of the input string is reached before any conver- |
       sions have been performed.

DETAILS ON SCANNING
       Scan operates by scanning string and format together.  If the next character in format  is
       a  blank  or tab then it matches any number of white space characters in string (including
       zero).  Otherwise, if it isn't a % character then it must  match  the  next  character  of
       string.	 When a % is encountered in format, it indicates the start of a conversion speci-
       fier.  A conversion specifier contains up to four fields after the %: a *, which indicates
       that  the  converted  value  is	to be discarded instead of assigned to a variable; a XPG3
       position specifier; a number indicating a maximum field width; and a conversion character.
       All of these fields are optional except for the conversion character.  The fields that are
       present must appear in the order given above.

       When scan finds a conversion specifier in format, it first skips any  white-space  charac-
       ters  in string (unless the specifier is [ or c).  Then it converts the next input charac-
       ters according to the conversion specifier and stores the result in the variable given  by
       the next argument to scan.

       If the % is followed by a decimal number and a $, as in ``%2$d'', then the variable to use
       is not taken from the next sequential argument.	Instead, it is taken  from  the  argument
       indicated by the number, where 1 corresponds to the first varName.  If there are any posi-
       tional specifiers in format then all of the specifiers must be positional.  Every  varName
       on  the	argument  list must correspond to exactly one conversion specifier or an error is
       generated, or in the inline case, any position can be specified at most once and the empty
       positions will be filled in with empty strings.

       The following conversion characters are supported:

       d	 The  input  field  must  be  a  decimal integer.  It is read in and the value is
		 stored in the variable as a decimal string.

       o	 The input field must be an octal integer. It is read in and the value is  stored
		 in the variable as a decimal string.  If the value exceeds MAX_INT (017777777777 |
		 on platforms using 32-bit integers), it will be truncated to a  signed  integer. |
		 Hence, 037777777777 will appear as -1 on a 32-bit machine.

       x	 The  input  field  must be a hexadecimal integer. It is read in and the value is
		 stored in the variable as a  decimal  string.	 If  the  value  exceeds  MAX_INT |
		 (0x7FFFFFFF  on  platforms  using  32-bit  integers),	it will be truncated to a |
		 signed integer.  Hence, 0xFFFFFFFF will appear as -1 on a 32-bit machine.

       u	 The input field must be a decimal integer.  The value is stored in the  variable
		 as an unsigned decimal integer string.

       i	 The input field must be an integer.  The base (i.e. decimal, octal, or hexadeci-
		 mal) is determined in the same fashion as  described  in  expr.   The	value  is
		 stored in the variable as a decimal string.

       c	 A  single character is read in and its binary value is stored in the variable as
		 a decimal string.  Initial white space is not skipped in this case, so the input
		 field	may  be  a  white-space character.  This conversion is different from the
		 ANSI standard in that the input field always consists of a single character  and
		 no field width may be specified.

       s	 The  input field consists of all the characters up to the next white-space char-
		 acter; the characters are copied to the variable.

       e or f or g
		 The input field must be a floating-point number consisting of an optional  sign,
		 a  string of decimal digits possibly containing a decimal point, and an optional
		 exponent consisting of an e or E followed by an optional sign and  a  string  of
		 decimal  digits.   It	is read in and stored in the variable as a floating-point
		 string.

       [chars]	 The input field consists of any number of characters  in  chars.   The  matching
		 string  is  stored in the variable.  If the first character between the brackets
		 is a ] then it is treated as part of chars rather than the closing  bracket  for
		 the  set.   If  chars	contains  a  sequence  of the form a-b then any character
		 between a and b (inclusive) will match.  If the first or last character  between
		 the  brackets is a -, then it is treated as part of chars rather than indicating
		 a range.

       [^chars]  The input field consists of any number of characters not in chars.  The matching
		 string  is stored in the variable.  If the character immediately following the ^
		 is a ] then it is treated as part of the set rather than the closing bracket for
		 the  set.   If  chars	contains  a  sequence  of the form a-b then any character
		 between a and b (inclusive) will be excluded from the set.  If the first or last
		 character  between  the  brackets  is	a  -, then it is treated as part of chars
		 rather than indicating a range.

       n	 No input is consumed from the input string.  Instead, the total number of  chac-
		 ters scanned from the input string so far is stored in the variable.

       The  number  of characters read from the input for a conversion is the largest number that
       makes sense for that particular conversion (e.g.  as many decimal digits as  possible  for
       %d, as many octal digits as possible for %o, and so on).  The input field for a given con-
       version terminates either when a white-space character is encountered or when the  maximum
       field  width has been reached, whichever comes first.  If a * is present in the conversion
       specifier then no variable is assigned and the next scan argument is not consumed.

DIFFERENCES FROM ANSI SSCANF
       The behavior of the scan command is the same as the behavior of the ANSI C  sscanf  proce-
       dure except for the following differences:

       [1]    %p conversion specifier is not currently supported.

       [2]    For %c conversions a single character value is converted to a decimal string, which
	      is then assigned to the corresponding varName; no field width may be specified  for
	      this conversion.

       [3]    The  l,  h, and L modifiers are ignored;	integer values are always converted as if
	      there were no modifier present and real values are always converted  as  if  the	l
	      modifier were present (i.e. type double is used for the internal representation).

       [4]    If  the  end  of	the input string is reached before any conversions have been per- |
	      formed and no variables are given, and empty string is returned.

SEE ALSO
       format(n), sscanf(3)

KEYWORDS
       conversion specifier, parse, scan

Tcl					       8.3					  scan(n)


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