1scan(n) Tcl Built-In Commands scan(n)
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8 scan - Parse string using conversion specifiers in the style of sscanf
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11 scan string format ?varName varName ...?
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15 This command parses substrings from an input string in a fashion simi‐
16 lar to the ANSI C sscanf procedure and returns a count of the number of
17 conversions performed, or -1 if the end of the input string is reached
18 before any conversions have been performed. String gives the input to
19 be parsed and format indicates how to parse it, using % conversion
20 specifiers as in sscanf. Each varName gives the name of a variable;
21 when a substring is scanned from string that matches a conversion spec‐
22 ifier, the substring is assigned to the corresponding variable. If no
23 varName variables are specified, then scan works in an inline manner,
24 returning the data that would otherwise be stored in the variables as a
25 list. In the inline case, an empty string is returned when the end of
26 the input string is reached before any conversions have been performed.
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29 Scan operates by scanning string and format together. If the next
30 character in format is a blank or tab then it matches any number of
31 white space characters in string (including zero). Otherwise, if it is
32 not a % character then it must match the next character of string.
33 When a % is encountered in format, it indicates the start of a conver‐
34 sion specifier. A conversion specifier contains up to four fields
35 after the %: a XPG3 position specifier (or a * to indicate the con‐
36 verted value is to be discarded instead of assigned to any variable); a
37 number indicating a maximum substring width; a size modifier; and a
38 conversion character. All of these fields are optional except for the
39 conversion character. The fields that are present must appear in the
40 order given above.
41 When scan finds a conversion specifier in format, it first skips any
43 white-space characters in string (unless the conversion character is [
44 or c). Then it converts the next input characters according to the
45 conversion specifier and stores the result in the variable given by the
46 next argument to scan.
47 OPTIONAL POSITIONAL SPECIFIER
49 If the % is followed by a decimal number and a $, as in “%2$d”, then
50 the variable to use is not taken from the next sequential argument.
51 Instead, it is taken from the argument indicated by the number, where 1
52 corresponds to the first varName. If there are any positional speci‐
53 fiers in format then all of the specifiers must be positional. Every
54 varName on the argument list must correspond to exactly one conversion
55 specifier or an error is generated, or in the inline case, any position
56 can be specified at most once and the empty positions will be filled in
57 with empty strings.
58 OPTIONAL SIZE MODIFIER
60 The size modifier field is used only when scanning a substring into one
61 of Tcl's integer values. The size modifier field dictates the integer
62 range acceptable to be stored in a variable, or, for the inline case,
63 in a position in the result list. The syntactically valid values for
64 the size modifier are h, L, l, and ll. The h size modifier value is
65 equivalent to the absence of a size modifier in the the conversion
66 specifier. Either one indicates the integer range to be stored is lim‐
67 ited to the same range produced by the int() function of the expr com‐
68 mand. The L size modifier is equivalent to the l size modifier. Either
69 one indicates the integer range to be stored is limited to the same
70 range produced by the wide() function of the expr command. The ll size
71 modifier indicates that the integer range to be stored is unlimited.
72 MANDATORY CONVERSION CHARACTER
74 The following conversion characters are supported:
75 d The input substring must be a decimal integer. It is read in
77 and the integer value is stored in the variable, truncated as
78 required by the size modifier value.
79 o The input substring must be an octal integer. It is read in and
81 the integer value is stored in the variable, truncated as
82 required by the size modifier value.
83 x or X The input substring must be a hexadecimal integer. It is read
85 in and the integer value is stored in the variable, truncated as
86 required by the size modifier value.
87 b The input substring must be a binary integer. It is read in and
89 the integer value is stored in the variable, truncated as
90 required by the size modifier value.
91 u The input substring must be a decimal integer. The integer
93 value is truncated as required by the size modifier value, and
94 the corresponding unsigned value for that truncated range is
95 computed and stored in the variable as a decimal string. The
96 conversion makes no sense without reference to a truncation
97 range, so the size modifier ll is not permitted in combination
98 with conversion character u.
99 i The input substring must be an integer. The base (i.e. decimal,
101 octal, or hexadecimal) is determined by the C convention (lead‐
102 ing 0 for octal; prefix 0x for hexadecimal). The integer value
103 is stored in the variable, truncated as required by the size
104 modifier value.
105 c A single character is read in and its Unicode value is stored in
107 the variable as an integer value. Initial white space is not
108 skipped in this case, so the input substring may be a white-
109 space character.
110 s The input substring consists of all the characters up to the
112 next white-space character; the characters are copied to the
113 variable.
114 e or f or g or E or G
116 The input substring must be a floating-point number consisting
117 of an optional sign, a string of decimal digits possibly con‐
118 taining a decimal point, and an optional exponent consisting of
119 an e or E followed by an optional sign and a string of decimal
120 digits. It is read in and stored in the variable as a floating-
121 point value.
122 [chars]
124 The input substring consists of one or more characters in chars.
125 The matching string is stored in the variable. If the first
126 character between the brackets is a ] then it is treated as part
127 of chars rather than the closing bracket for the set. If chars
128 contains a sequence of the form a-b then any character between a
129 and b (inclusive) will match. If the first or last character
130 between the brackets is a -, then it is treated as part of chars
131 rather than indicating a range.
132 [^chars]
134 The input substring consists of one or more characters not in
135 chars. The matching string is stored in the variable. If the
136 character immediately following the ^ is a ] then it is treated
137 as part of the set rather than the closing bracket for the set.
138 If chars contains a sequence of the form a-b then any character
139 between a and b (inclusive) will be excluded from the set. If
140 the first or last character between the brackets is a -, then it
141 is treated as part of chars rather than indicating a range
142 value.
143 n No input is consumed from the input string. Instead, the total
145 number of characters scanned from the input string so far is
146 stored in the variable.
147 The number of characters read from the input for a conversion is the
149 largest number that makes sense for that particular conversion (e.g.
150 as many decimal digits as possible for %d, as many octal digits as pos‐
151 sible for %o, and so on). The input substring for a given conversion
152 terminates either when a white-space character is encountered or when
153 the maximum substring width has been reached, whichever comes first.
154 If a * is present in the conversion specifier then no variable is
155 assigned and the next scan argument is not consumed.
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158 The behavior of the scan command is the same as the behavior of the
159 ANSI C sscanf procedure except for the following differences:
160 [1] %p conversion specifier is not supported.
162 [2] For %c conversions a single character value is converted to a
164 decimal string, which is then assigned to the corresponding var‐
165 Name; no substring width may be specified for this conversion.
166 [3] The h modifier is always ignored and the l and L modifiers are
168 ignored when converting real values (i.e. type double is used
169 for the internal representation). The ll modifier has no sscanf
170 counterpart.
171 [4] If the end of the input string is reached before any conversions
173 have been performed and no variables are given, an empty string
174 is returned.
175
177 Convert a UNICODE character to its numeric value:
178 set char "x"
180 set value [scan $char %c]
181 Parse a simple color specification of the form #RRGGBB using hexadeci‐
183 mal conversions with substring sizes:
184 set string "#08D03F"
186 scan $string "#%2x%2x%2x" r g b
187 Parse a HH:MM time string, noting that this avoids problems with octal
189 numbers by forcing interpretation as decimals (if we did not care, we
190 would use the %i conversion instead):
191 set string "08:08" ;# *Not* octal!
193 if {[scan $string "%d:%d" hours minutes] != 2} {
194 error "not a valid time string"
195 }
196 # We have to understand numeric ranges ourselves...
197 if {$minutes < 0 || $minutes > 59} {
198 error "invalid number of minutes"
199 }
200 Break a string up into sequences of non-whitespace characters (note the
202 use of the %n conversion so that we get skipping over leading white‐
203 space correct):
204 set string " a string {with braced words} + leading space "
206 set words {}
207 while {[scan $string %s%n word length] == 2} {
208 lappend words $word
209 set string [string range $string $length end]
210 }
211 Parse a simple coordinate string, checking that it is complete by look‐
213 ing for the terminating character explicitly:
214 set string "(5.2,-4e-2)"
216 # Note that the spaces before the literal parts of
217 # the scan pattern are significant, and that ")" is
218 # the Unicode character \u0029
219 if {
220 [scan $string " (%f ,%f %c" x y last] != 3
221 || $last != 0x0029
222 } then {
223 error "invalid coordinate string"
224 }
225 puts "X=$x, Y=$y"
226 An interactive session demonstrating the truncation of integer values
228 determined by size modifiers:
229 % set tcl_platform(wordSize)
231 4
232 % scan 20000000000000000000 %d
233 2147483647
234 % scan 20000000000000000000 %ld
235 9223372036854775807
236 % scan 20000000000000000000 %lld
237 20000000000000000000
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240 format(n), sscanf(3)
241
243 conversion specifier, parse, scan
244Tcl 8.4 scan(n)