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.

EXAMPLES
       Parse a simple color specification of the form #RRGGBB using  hexadeci-
       mal conversions with field 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"


SEE ALSO
       format(n), sscanf(3)


KEYWORDS
