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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 ...?
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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.

       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.

       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.

       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
		 required 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.

       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  trunca-
		 tion  range, so the size modifier ll is not permitted in com-
		 bination with conversion character u.

       i	 The input substring must be an	integer.  The base (i.e. deci-
		 mal, binary, octal, or	hexadecimal) is	determined in the same
		 fashion as described in expr.	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 consist-
		 ing of	an optional sign, a string of decimal digits  possibly
		 containing a decimal point, and an optional exponent consist-
		 ing 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  ex-
		 cluded	 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 to-
		 tal 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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