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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 substrings from an input string in a fashion simi-
       lar to 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 substring	is scanned from	string that matches a conversion spec-
       ifier, the substring is 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 conversions 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 is
       not  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 af-
       ter the %: a XPG3 position specifier (or	a * to indicate	the  converted
       value is	to be discarded	instead	of assigned to any variable); a	number
       indicating a maximum substring width; a size modifier; 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 conversion character 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 argument to	scan.

   OPTIONAL POSITIONAL SPECIFIER
       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, or in the inline case, any position
       can be specified	at most	once and the empty positions will be filled in
       with empty strings.

   OPTIONAL SIZE MODIFIER
       The size	modifier field is used only when scanning a substring into one
       of Tcl's	integer	values.	 The size modifier field dictates the  integer
       range  acceptable  to be	stored in a variable, or, for the inline case,
       in a position in	the result list.  The syntactically valid  values  for
       the  size  modifier  are	h, L, l, and ll.  The h	size modifier value is
       equivalent to the absence of a size  modifier  in  the  the  conversion
       specifier.  Either one indicates	the integer range to be	stored is lim-
       ited to the same	range produced by the int() function of	the expr  com-
       mand.  The L size modifier is equivalent	to the l size modifier.	Either
       one indicates the integer range to be stored is	limited	 to  the  same
       range produced by the wide() function of	the expr command.  The ll size
       modifier	indicates that the integer range to be stored is unlimited.

   MANDATORY CONVERSION	CHARACTER
       The following conversion	characters are supported:

       d      The input	substring must be a decimal integer.  It  is  read  in
	      and  the	integer	 value is stored in the	variable, truncated as
	      required by the size modifier value.

       o      The input	substring must be an octal integer. It is read in  and
	      the  integer  value  is stored in	the variable, truncated	as re-
	      quired by	the size modifier value.

       x or X The input	substring must be a hexadecimal	integer.  It  is  read
	      in and the integer value is stored in the	variable, truncated as
	      required by the size modifier value.

       b      The input	substring must be a binary integer.  It	is read	in and
	      the  integer  value  is stored in	the variable, truncated	as re-
	      quired by	the size modifier value.

       u      The input	substring must be  a  decimal  integer.	  The  integer
	      value  is	 truncated as required by the size modifier value, and
	      the corresponding	unsigned value for  that  truncated  range  is
	      computed	and  stored  in	the variable as	a decimal string.  The
	      conversion makes no sense	 without  reference  to	 a  truncation
	      range,  so  the size modifier ll is not permitted	in combination
	      with conversion character	u.

       i      The input	substring must be an integer.  The base	(i.e. decimal,
	      octal,  or hexadecimal) is determined by the C convention	(lead-
	      ing 0 for	octal; prefix 0x for hexadecimal).  The	integer	 value
	      is  stored  in  the  variable, truncated as required by the size
	      modifier value.

       c      A	single character is read in and	its Unicode value is stored in
	      the  variable  as	 an integer value.  Initial white space	is not
	      skipped in this case, so the input substring  may	 be  a	white-
	      space character.

       s      The  input  substring  consists  of all the characters up	to the
	      next white-space character; the characters  are  copied  to  the
	      variable.

       e or f or g or E	or G
	      The  input  substring 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 value.

       [chars]
	      The input	substring consists of one or more 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  substring  consists of one or	more 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
	      value.

       n      No  input	is consumed from the input string.  Instead, the total
	      number of	characters 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 substring for a  given  conversion
       terminates  either  when	a white-space character	is encountered or when
       the maximum substring width has been reached,  whichever	 comes	first.
       If  a  *	is present in the conversion specifier then no variable	is as-
       signed 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 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 substring width may be specified	for this conversion.

       [3]    The  h  modifier is always ignored and the l and L modifiers are
	      ignored when converting real values (i.e.	type  double  is  used
	      for the internal representation).	 The ll	modifier has no	sscanf
	      counterpart.

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

EXAMPLES
       Convert a UNICODE character to its numeric value:

	      set char "x"
	      set value	[scan $char %c]

       Parse a simple color specification of the form #RRGGBB using  hexadeci-
       mal conversions with substring sizes:

	      set string "#08D03F"
	      scan $string "#%2x%2x%2x"	r g b

       Parse  a	HH:MM time string, noting that this avoids problems with octal
       numbers by forcing interpretation as decimals (if we did	not  care,  we
       would use the %i	conversion instead):

	      set string "08:08"   ;# *Not* octal!
	      if {[scan	$string	"%d:%d"	hours minutes] != 2} {
		  error	"not a valid time string"
	      }
	      #	We have	to understand numeric ranges ourselves...
	      if {$minutes < 0 || $minutes > 59} {
		  error	"invalid number	of minutes"
	      }

       Break a string up into sequences	of non-whitespace characters (note the
       use of the %n conversion	so that	we get skipping	 over  leading	white-
       space correct):

	      set string " a string {with braced words}	+ leading space	"
	      set words	{}
	      while {[scan $string %s%n	word length] ==	2} {
		  lappend words	$word
		  set string [string range $string $length end]
	      }

       Parse a simple coordinate string, checking that it is complete by look-
       ing for the terminating character explicitly:

	      set string "(5.2,-4e-2)"
	      #	Note that the spaces before the	literal	parts of
	      #	the scan pattern are significant, and that ")" is
	      #	the Unicode character \u0029
	      if {
		  [scan	$string	" (%f ,%f %c" x	y last]	!= 3
		  || $last != 0x0029
	      }	then {
		  error	"invalid coordinate string"
	      }
	      puts "X=$x, Y=$y"

       An interactive session demonstrating the	truncation of  integer	values
       determined by size modifiers:

	      %	set tcl_platform(wordSize)
	      4
	      %	scan 20000000000000000000 %d
	      2147483647
	      %	scan 20000000000000000000 %ld
	      9223372036854775807
	      %	scan 20000000000000000000 %lld
	      20000000000000000000

SEE ALSO
       format(n), sscanf(3)

KEYWORDS
       conversion specifier, parse, scan

Tcl				      8.4			       scan(n)

NAME | SYNOPSIS | INTRODUCTION | DETAILS ON SCANNING | DIFFERENCES FROM ANSI SSCANF | EXAMPLES | SEE ALSO | KEYWORDS

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