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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16 This command parses fields from an input string in the same fashion as
17 the ANSI C sscanf procedure and returns a count of the number of con‐
18 versions performed, or -1 if the end of the input string is reached
19 before any conversions have been performed. String gives the input to
20 be parsed and format indicates how to parse it, using % conversion
21 specifiers as in sscanf. Each varName gives the name of a variable;
22 when a field is scanned from string the result is converted back into a
23 string and assigned to the corresponding variable. If no varName vari‐
24 ables are specified, then scan works in an inline manner, returning the
25 data that would otherwise be stored in the variables as a list. In the
26 inline case, an empty string is returned when the end of the input
27 string is reached before any conversions have been performed.
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30 Scan operates by scanning string and format together. If the next
31 character in format is a blank or tab then it matches any number of
32 white space characters in string (including zero). Otherwise, if it
33 isn't a % character then it must match the next character of string.
34 When a % is encountered in format, it indicates the start of a conver‐
35 sion specifier. A conversion specifier contains up to four fields │
36 after the %: a *, which indicates that the converted value is to be │
37 discarded instead of assigned to a variable; a XPG3 position specifier; │
38 a number indicating a maximum field width; a field size modifier; and a │
39 conversion character. All of these fields are optional except for the
40 conversion character. The fields that are present must appear in the
41 order given above.
42 When scan finds a conversion specifier in format, it first skips any
44 white-space characters in string (unless the specifier is [ or c).
45 Then it converts the next input characters according to the conversion
46 specifier and stores the result in the variable given by the next argu‐
47 ment to scan.
48 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 The following conversion characters are supported:
60 d The input field must be a decimal integer. It is read in and
62 the value is stored in the variable as a decimal string. If │
63 the l or L field size modifier is given, the scanned value │
64 will have an internal representation that is at least 64-bits │
65 in size.
66 o The input field must be an octal integer. It is read in and
68 the value is stored in the variable as a decimal string. If │
69 the l or L field size modifier is given, the scanned value │
70 will have an internal representation that is at least 64-bits │
71 in size. If the value exceeds MAX_INT (017777777777 on plat‐ │
72 forms using 32-bit integers when the l and L modifiers are │
73 not given), it will be truncated to a signed integer. Hence, │
74 037777777777 will appear as -1 on a 32-bit machine by │
75 default.
76 x The input field must be a hexadecimal integer. It is read in
78 and the value is stored in the variable as a decimal string. │
79 If the l or L field size modifier is given, the scanned value │
80 will have an internal representation that is at least 64-bits │
81 in size. If the value exceeds MAX_INT (0x7FFFFFFF on plat‐ │
82 forms using 32-bit integers when the l and L modifiers are │
83 not given), it will be truncated to a signed integer. Hence, │
84 0xFFFFFFFF will appear as -1 on a 32-bit machine.
85 u The input field must be a decimal integer. The value is
87 stored in the variable as an unsigned decimal integer string. │
88 If the l or L field size modifier is given, the scanned value │
89 will have an internal representation that is at least 64-bits │
90 in size.
91 i The input field must be an integer. The base (i.e. decimal,
93 octal, or hexadecimal) is determined in the same fashion as
94 described in expr. The value is stored in the variable as a
95 decimal string. If the l or L field size modifier is given, │
96 the scanned value will have an internal representation that │
97 is at least 64-bits in size.
98 c A single character is read in and its binary value is stored
100 in the variable as a decimal string. Initial white space is
101 not skipped in this case, so the input field may be a white-
102 space character. This conversion is different from the ANSI
103 standard in that the input field always consists of a single
104 character and no field width may be specified.
105 s The input field consists of all the characters up to the next
107 white-space character; the characters are copied to the vari‐
108 able.
109 e or f or g
111 The input field must be a floating-point number consisting of
112 an optional sign, a string of decimal digits possibly con‐
113 taining a decimal point, and an optional exponent consisting
114 of an e or E followed by an optional sign and a string of
115 decimal digits. It is read in and stored in the variable as
116 a floating-point string.
117 [chars] The input field consists of any number of characters in
119 chars. The matching string is stored in the variable. If
120 the first character between the brackets is a ] then it is
121 treated as part of chars rather than the closing bracket for
122 the set. If chars contains a sequence of the form a-b then
123 any character between a and b (inclusive) will match. If the
124 first or last character between the brackets is a -, then it
125 is treated as part of chars rather than indicating a range.
126 [^chars] The input field consists of any number of characters not in
128 chars. The matching string is stored in the variable. If
129 the character immediately following the ^ is a ] then it is
130 treated as part of the set rather than the closing bracket
131 for the set. If chars contains a sequence of the form a-b
132 then any character between a and b (inclusive) will be
133 excluded from the set. If the first or last character
134 between the brackets is a -, then it is treated as part of
135 chars rather than indicating a range.
136 n No input is consumed from the input string. Instead, the
138 total number of characters scanned from the input string so
139 far is stored in the variable.
140 The number of characters read from the input for a conversion is the
142 largest number that makes sense for that particular conversion (e.g.
143 as many decimal digits as possible for %d, as many octal digits as pos‐
144 sible for %o, and so on). The input field for a given conversion ter‐
145 minates either when a white-space character is encountered or when the
146 maximum field width has been reached, whichever comes first. If a * is
147 present in the conversion specifier then no variable is assigned and
148 the next scan argument is not consumed.
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151 The behavior of the scan command is the same as the behavior of the
152 ANSI C sscanf procedure except for the following differences:
153 [1] %p conversion specifier is not currently supported.
155 [2] For %c conversions a single character value is converted to a
157 decimal string, which is then assigned to the corresponding var‐
158 Name; no field width may be specified for this conversion.
159 [3] The h modifier is always ignored and the l and L modifiers are │
161 ignored when converting real values (i.e. type double is used │
162 for the internal representation).
163 [4] If the end of the input string is reached before any conversions
165 have been performed and no variables are given, an empty string
166 is returned.
167
169 Parse a simple color specification of the form #RRGGBB using hexadeci‐
170 mal conversions with field sizes:
171 set string "#08D03F"
172 scan $string "#%2x%2x%2x" r g b
173 Parse a HH:MM time string, noting that this avoids problems with octal
175 numbers by forcing interpretation as decimals (if we did not care, we
176 would use the %i conversion instead):
177 set string "08:08" ;# *Not* octal!
178 if {[scan $string "%d:%d" hours minutes] != 2} {
179 error "not a valid time string"
180 }
181 # We have to understand numeric ranges ourselves...
182 if {$minutes < 0 || $minutes > 59} {
183 error "invalid number of minutes"
184 }
185 Break a string up into sequences of non-whitespace characters (note the
187 use of the %n conversion so that we get skipping over leading white‐
188 space correct):
189 set string " a string {with braced words} + leading space "
190 set words {}
191 while {[scan $string %s%n word length] == 2} {
192 lappend words $word
193 set string [string range $string $length end]
194 }
195 Parse a simple coordinate string, checking that it is complete by look‐
197 ing for the terminating character explicitly:
198 set string "(5.2,-4e-2)"
199 # Note that the spaces before the literal parts of
200 # the scan pattern are significant, and that ")" is
201 # the Unicode character \u0029
202 if {
203 [scan $string " (%f ,%f %c" x y last] != 3
204 || $last != 0x0029
205 } then {
206 error "invalid coordinate string"
207 }
208 puts "X=$x, Y=$y"
209
212 format(n), sscanf(3)
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216 conversion specifier, parse, scan
217Tcl 8.4 scan(n)