Provided by: tcl8.6-doc_8.6.14+dfsg-1build1_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

Tcl                                                    8.4                                            scan(3tcl)