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 fields sucessfully parsed. 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.
DETAILS ON SCANNING
Scan operates by scanning string and formatString
together. If the next character in formatString is a
blank or tab then it is ignored. Otherwise, if it isn't a
% character then it must match the next non-white-space
character of string. When a % is encountered in format-
String, it indicates the start of a conversion specifier.
A conversion specifier contains three fields after the %:
a *, which indicates that the converted value is to be
discarded instead of assigned to a variable; a number
indicating a maximum field width; and a conversion charac-
ter. All of these fields are optional except for the con-
version character.
When scan finds a conversion specifier in formatString, it
first skips any white-space characters in string. Then it
converts the next input characters according to the con-
version specifier and stores the result in the variable
given by the next argument to scan. The following conver-
sion characters are supported:
d The input field must be a decimal integer. It
is read in and the value is stored in the vari-
able 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.
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.
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 char-
acters 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 dec-
imal 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 char-
acters 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.
[^chars] The input field consists of any number of char-
acters not in chars. The matching string is
stored in the variable. If the character imme-
diately following the ^ is a ] then it is
treated as part of the set rather than the clos-
ing bracket for the set.
The number of characters read from the input for a conver-
sion is the largest number that makes sense for that par-
ticular conversion (e.g. as many decimal digits as possi-
ble 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 behav-
ior of the ANSI C sscanf procedure except for the follow-
ing differences:
[1] %p and %n conversion specifiers are not currently
supported.
[2] For %c conversions a single character value is con-
verted 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 con-
verted as if the l modifier were present (i.e. type
double is used for the internal representation).
KEYWORDS
conversion specifier, parse, scan