scan(n) 						       Tcl Built-In Commands							   scan(n)

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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  fields  from an input string in the same fashion as 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 field is scanned from string the result is converted back into a string and 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 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 conversion 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; and a conversion character.  All of these fields are optional except for the conversion  charac-
       ter.  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
       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 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.

       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 |
		 value exceeds MAX_INT (017777777777 on platforms using 32-bit integers), it will  be  truncated  to  a  signed  integer.   Hence, |
		 037777777777 will appear as -1 on a 32-bit machine.

       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 |
		 value exceeds MAX_INT (0x7FFFFFFF on platforms using 32-bit integers),  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.

       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.

       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 variable.

       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 containing  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 char-
		 acter 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 chacters 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 field  for  a  given	conversion
       terminates  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  varName;
	      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).

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

SEE ALSO

       format(n), sscanf(3)

KEYWORDS

       conversion specifier, parse, scan

Tcl									8.3								   scan(n)