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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.  If no varName vari‐
       ables 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
       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; a field 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  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, 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 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.   If │
		 the  l	 or  L field size modifier is given, the scanned value │
		 will have an internal representation that is at least 64-bits │
		 in size.

       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.   If │
		 the  l	 or  L field size modifier is given, the scanned value │
		 will have an internal representation that is at least 64-bits │
		 in size.  If the value exceeds MAX_INT (017777777777 on plat‐ │
		 forms using 32-bit integers when the l and  L	modifiers  are │
		 not given), it will be truncated to a signed integer.	Hence, │
		 037777777777 will  appear  as	-1  on	a  32-bit  machine  by │
		 default.

       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. │
		 If the l or L field size modifier is given, the scanned value │
		 will have an internal representation that is at least 64-bits │
		 in  size.   If the value exceeds MAX_INT (0x7FFFFFFF on plat‐ │
		 forms using 32-bit integers when the l and  L	modifiers  are │
		 not given), it will be truncated to a signed integer.	Hence, │
		 0xFFFFFFFF will appear as -1 on a 32-bit machine.

       u	 The input field must be a  decimal  integer.	The  value  is
		 stored in the variable as an unsigned decimal integer string. │
		 If the l or L field size modifier is given, the scanned value │
		 will have an internal representation that is at least 64-bits │
		 in size.

       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.  If the l or L field size modifier is given, │
		 the scanned value will have an internal  representation  that │
		 is at least 64-bits in size.

       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 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 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 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).

       [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.

SEE ALSO
       format(n), sscanf(3)

KEYWORDS
       conversion specifier, parse, scan

Tcl				      8.4			       scan(n)
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