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Updated: Thursday, June 13, 2019
 
 

scan (1t)

Name

scan - Parse string using conversion specifiers in the style of sscanf

Synopsis

scan string format ?varName varName ...?

Description

scan(1t)                     Tcl Built-In Commands                    scan(1t)



______________________________________________________________________________

NAME
       scan - Parse string using conversion specifiers in the style of sscanf

SYNOPSIS
       scan string format ?varName varName ...?
______________________________________________________________________________

INTRODUCTION
       This  command parses substrings from an input string in a fashion simi-
       lar 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 spec-
       ifier, 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  conver-
       sion  specifier.   A  conversion  specifier  contains up to four fields
       after the %: a XPG3 position specifier (or a *  to  indicate  the  con-
       verted 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  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.

   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 lim-
       ited to the same range produced by the int() function of the expr  com-
       mand.  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 (lead-
              ing 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  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 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 pos-
       sible 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 var-
              Name; 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  hexadeci-
       mal 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  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"

       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


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       +---------------+------------------+
       |ATTRIBUTE TYPE | ATTRIBUTE VALUE  |
       +---------------+------------------+
       |Availability   | runtime/tcl-8    |
       +---------------+------------------+
       |Stability      | Uncommitted      |
       +---------------+------------------+
SEE ALSO
       format(n), sscanf(3)

KEYWORDS
       conversion specifier, parse, scan



NOTES
       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source was downloaded from  http://prdownloads.sourceforge.net/tcl/tcl-
       core8.6.7-src.tar.gz

       Further information about this software can be found on the open source
       community website at https://www.tcl.tk/.



Tcl                                   8.4                             scan(1t)