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 If the % is followed by a decimal number and a $, as in “%2$d”, then
49 the variable to use is not taken from the next sequential argument.
50 Instead, it is taken from the argument indicated by the number, where 1
51 corresponds to the first varName. If there are any positional speci‐
52 fiers in format then all of the specifiers must be positional. Every
53 varName on the argument list must correspond to exactly one conversion
54 specifier or an error is generated, or in the inline case, any position
55 can be specified at most once and the empty positions will be filled in
56 with empty strings.
57 The size modifier field is used only when scanning a substring into one │
59 of Tcl's integer values. The size modifier field dictates the integer │
60 range acceptable to be stored in a variable, or, for the inline case, │
61 in a position in the result list. The syntactically valid values for │
62 the size modifier are h, L, l, and ll. The h size modifier value is │
63 equivalent to the absence of a size modifier in the the conversion │
64 specifier. Either one indicates the integer range to be stored is lim‐ │
65 ited to the same range produced by the int() function of the expr com‐ │
66 mand. The L size modifier is equivalent to the l size modifier. Either │
67 one indicates the integer range to be stored is limited to the same │
68 range produced by the wide() function of the expr command. The ll size │
69 modifier indicates that the integer range to be stored is unlimited.
70 The following conversion characters are supported:
72 d The input substring must be a decimal integer. It is read in
74 and the integer value is stored in the variable, truncated as
75 required by the size modifier value.
76 o The input substring must be an octal integer. It is read in
78 and the integer value is stored in the variable, truncated as
79 required by the size modifier value.
80 x The input substring must be a hexadecimal integer. It is
82 read in and the integer value is stored in the variable,
83 truncated as required by the size modifier value.
84 u The input substring must be a decimal integer. The integer
86 value is truncated as required by the size modifier value,
87 and the corresponding unsigned value for that truncated range
88 is computed and stored in the variable as a decimal string.
89 The conversion makes no sense without reference to a trunca‐
90 tion range, so the size modifier ll is not permitted in com‐
91 bination with conversion character u.
92 i The input substring must be an integer. The base (i.e. deci‐
94 mal, binary, octal, or hexadecimal) is determined in the same
95 fashion as described in expr. The integer value is stored in
96 the variable, truncated as required by the size modifier
97 value.
98 c A single character is read in and its Unicode value is stored
100 in the variable as an integer value. Initial white space is
101 not skipped in this case, so the input substring may be a
102 white-space character.
103 s The input substring consists of all the characters up to the
105 next white-space character; the characters are copied to the
106 variable.
107 e or f or g
109 The input substring must be a floating-point number consist‐
110 ing of an optional sign, a string of decimal digits possibly
111 containing a decimal point, and an optional exponent consist‐
112 ing of an e or E followed by an optional sign and a string of
113 decimal digits. It is read in and stored in the variable as
114 a floating-point value.
115 [chars] The input substring consists of one or more characters in
117 chars. The matching string is stored in the variable. If
118 the first character between the brackets is a ] then it is
119 treated as part of chars rather than the closing bracket for
120 the set. If chars contains a sequence of the form a-b then
121 any character between a and b (inclusive) will match. If the
122 first or last character between the brackets is a -, then it
123 is treated as part of chars rather than indicating a range.
124 [^chars] The input substring consists of one or more characters not in
126 chars. The matching string is stored in the variable. If
127 the character immediately following the ^ is a ] then it is
128 treated as part of the set rather than the closing bracket
129 for the set. If chars contains a sequence of the form a-b
130 then any character between a and b (inclusive) will be
131 excluded from the set. If the first or last character
132 between the brackets is a -, then it is treated as part of
133 chars rather than indicating a range value.
134 n No input is consumed from the input string. Instead, the
136 total number of characters scanned from the input string so
137 far is stored in the variable.
138 The number of characters read from the input for a conversion is the
140 largest number that makes sense for that particular conversion (e.g.
141 as many decimal digits as possible for %d, as many octal digits as pos‐
142 sible for %o, and so on). The input substring for a given conversion
143 terminates either when a white-space character is encountered or when
144 the maximum substring width has been reached, whichever comes first.
145 If a * is present in the conversion specifier then no variable is
146 assigned and the next scan argument is not consumed.
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149 The behavior of the scan command is the same as the behavior of the
150 ANSI C sscanf procedure except for the following differences:
151 [1] %p conversion specifier is not supported.
153 [2] For %c conversions a single character value is converted to a
155 decimal string, which is then assigned to the corresponding var‐
156 Name; no substring width may be specified for this conversion.
157 [3] The h modifier is always ignored and the l and L modifiers are
159 ignored when converting real values (i.e. type double is used
160 for the internal representation). The ll modifier has no sscanf
161 counterpart.
162 [4] If the end of the input string is reached before any conversions
164 have been performed and no variables are given, an empty string
165 is returned.
166
168 Convert a UNICODE character to its numeric value:
169 set char "x"
170 set value [scan $char %c]
171 Parse a simple color specification of the form #RRGGBB using hexadeci‐
173 mal conversions with substring sizes:
174 set string "#08D03F"
175 scan $string "#%2x%2x%2x" r g b
176 Parse a HH:MM time string, noting that this avoids problems with octal
178 numbers by forcing interpretation as decimals (if we did not care, we
179 would use the %i conversion instead):
180 set string "08:08" ;# *Not* octal!
181 if {[scan $string "%d:%d" hours minutes] != 2} {
182 error "not a valid time string"
183 }
184 # We have to understand numeric ranges ourselves...
185 if {$minutes < 0 || $minutes > 59} {
186 error "invalid number of minutes"
187 }
188 Break a string up into sequences of non-whitespace characters (note the
190 use of the %n conversion so that we get skipping over leading white‐
191 space correct):
192 set string " a string {with braced words} + leading space "
193 set words {}
194 while {[scan $string %s%n word length] == 2} {
195 lappend words $word
196 set string [string range $string $length end]
197 }
198 Parse a simple coordinate string, checking that it is complete by look‐
200 ing for the terminating character explicitly:
201 set string "(5.2,-4e-2)"
202 # Note that the spaces before the literal parts of
203 # the scan pattern are significant, and that ")" is
204 # the Unicode character \u0029
205 if {
206 [scan $string " (%f ,%f %c" x y last] != 3
207 || $last != 0x0029
208 } then {
209 error "invalid coordinate string"
210 }
211 puts "X=$x, Y=$y"
212 An interactive session demonstrating the truncation of integer values │
214 determined by size modifiers: │
215 % set tcl_platform(wordSize) │
216 4 │
217 % scan 20000000000000000000 %d │
218 2147483647 │
219 % scan 20000000000000000000 %ld │
220 9223372036854775807 │
221 % scan 20000000000000000000 %lld │
222 20000000000000000000 │
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225 format(n), sscanf(3)
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228 conversion specifier, parse, scan
229Tcl 8.4 scan(n)