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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  formatString  together.   If  the
       next  character	in  formatString is a blank or tab then it matches any
       number of white space characters in string  (including  zero).	Other‐
       wise,  if  it isn't a % character then it must match the next character
       of string.  When a % is encountered in formatString, it	indicates  the
       start of a conversion specifier.	 A conversion specifier contains three
       fields after the %: a *, which indicates that the converted value is to
       be  discarded  instead of assigned to a variable; a number indicating a
       maximum field width; and a conversion character.	 All of	 these	fields
       are optional except for the conversion character.

       When  scan finds a conversion specifier in formatString, it first skips
       any white-space characters in string.  Then it converts the next	 input
       characters  according to the conversion specifier and stores the result
       in the variable given by the next argument to scan.  The following con‐
       version 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.

       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.

       [^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.

       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 and %n conversion specifiers are 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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