Provided by: tcl8.6-doc_8.6.9+dfsg-2_all bug

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 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  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 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.

   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 specifiers 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 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.

   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 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.

       b      The  input substring must be a binary 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,  octal,  or
              hexadecimal)  is determined by the C convention (leading 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 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
              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(3tcl), sscanf(3)

KEYWORDS

       conversion specifier, parse, scan