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 similar 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 specifier, the substring is assigned to the corresponding vari-
       able.  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 conversion specifier.  A conversion specifier contains up to four fields
       after 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
       specifiers in format then all of the specifiers must be positional.  Every varName on the argument list must correspond to exactly one con-
       version	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 limited to the same range produced by the int() function of |
       the expr command.  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	 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 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, 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  vari-
		 able.

       e or f or g
		 The  input substring must be a floating-point number consisting of an optional sign, a string of decimal digits possibly contain-
		 ing a decimal point, and an optional exponent consisting of an e or E followed by an optional sign and a string of  decimal  dig-
		 its.  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 possible 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 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 supported.

       [2]    For %c conversions a single character value is converted to a decimal string, which is then assigned to the  corresponding  varName;
	      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 hexadecimal 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
       whitespace 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 looking 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)