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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  con‐
       versions	 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.

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  conver‐
       sion  specifier.	  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  characters	in  string  (unless  the specifier is [ or c).
       Then it converts the next input characters according to the  conversion
       specifier and stores the result in the variable given by the next argu‐
       ment 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 positional speci‐ │
       fiers 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.

       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.

       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.  │

       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  hexadecimal) 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 character; the characters are copied to the vari‐
		 able.

       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 con‐
		 taining 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 chacters 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 pos‐
       sible  for %o, and so on).  The input field for a given conversion ter‐
       minates 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 procedure 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 var‐
	      Name; 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).

KEYWORDS
       conversion specifier, parse, scan

Tcl								       scan(n)
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