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 fields from an input string in the
same fashion as 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 field is scanned from string the result
is converted back into a string and assigned to the corre
sponding 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 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 con
version 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; and a conversion character. All of
these fields are optional except for the conversion char
acter. 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
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.
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 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. If the value exceeds |
MAX_INT (017777777777 on platforms using 32-bit |
integers), it will be truncated to a signed |
integer. Hence, 037777777777 will appear as -1 |
on a 32-bit machine.
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 value |
exceeds MAX_INT (0x7FFFFFFF on platforms using |
32-bit integers), 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.
i The input field must be an integer. The base
(i.e. decimal, octal, or hexadecimal) is deter
mined in the same fashion as described in expr.
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.
The input field must be a floating-point number
consisting of an optional sign, a string of dec
imal 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 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. If chars contains a sequence of the form
a-b then any character between a and b (inclu
sive) will match. If the first or last charac
ter 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 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. 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 chacters scanned
from the input string so far is stored in the
variable.
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:
[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).
[4] If the end of the input string is reached before |
any conversions have been performed and no vari |
ables are given, and empty string is returned.
SEE ALSO
format(n), sscanf(3)
KEYWORDS
conversion specifier, parse, scan
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