1format(n)                    Tcl Built-In Commands                   format(n)
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NAME

8       format - Format a string in the style of sprintf
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SYNOPSIS

11       format formatString ?arg arg ...?
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14

INTRODUCTION

16       This  command  generates a formatted string in a fashion similar to the
17       ANSI C sprintf procedure.  FormatString indicates  how  to  format  the
18       result, using % conversion specifiers as in sprintf, and the additional
19       arguments, if any, provide values to be substituted  into  the  result.
20       The return value from format is the formatted string.
21

DETAILS ON FORMATTING

23       The command operates by scanning formatString from left to right.  Each
24       character from the format string  is  appended  to  the  result  string
25       unless  it  is  a percent sign.  If the character is a % then it is not
26       copied to the result string.  Instead, the characters following  the  %
27       character are treated as a conversion specifier.  The conversion speci‐
28       fier controls the conversion of the next successive arg to a particular
29       format  and the result is appended to the result string in place of the
30       conversion specifier.  If there are multiple conversion  specifiers  in
31       the  format  string, then each one controls the conversion of one addi‐
32       tional arg.  The format command must be given enough args to  meet  the
33       needs of all of the conversion specifiers in formatString.
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35       Each  conversion  specifier  may  contain up to six different parts: an
36       XPG3 position specifier, a set of flags, a minimum field width, a  pre‐
37       cision,  a  size  modifier,  and  a conversion character.  Any of these
38       fields may be omitted except for the conversion character.  The  fields
39       that  are present must appear in the order given above.  The paragraphs
40       below discuss each of these fields in turn.
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42   OPTIONAL POSITIONAL SPECIFIER
43       If the % is followed by a decimal number and a $, as  in  “%2$d”,  then
44       the  value  to  convert is not taken from the next sequential argument.
45       Instead, it is taken from the argument indicated by the number, where 1
46       corresponds  to  the  first  arg.  If the conversion specifier requires
47       multiple arguments because of * characters in the specifier  then  suc‐
48       cessive  arguments  are  used,  starting with the argument given by the
49       number.  This follows the XPG3 conventions for  positional  specifiers.
50       If  there are any positional specifiers in formatString then all of the
51       specifiers must be positional.
52
53   OPTIONAL FLAGS
54       The second portion of a conversion specifier may  contain  any  of  the
55       following flag characters, in any order:
56
57       -         Specifies  that  the converted argument should be left-justi‐
58                 fied in its field (numbers are normally right-justified  with
59                 leading spaces if needed).
60
61       +         Specifies that a number should always be printed with a sign,
62                 even if positive.
63
64       space     Specifies that a space should be added to  the  beginning  of
65                 the number if the first character is not a sign.
66
67       0         Specifies  that  the number should be padded on the left with
68                 zeroes instead of spaces.
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70       #         Requests an alternate output form. For o conversions it guar‐
71                 antees  that the first digit is always 0.  For x or X conver‐
72                 sions, 0x or 0X (respectively) will be added to the beginning
73                 of  the result unless it is zero.  For b conversions, 0b will
74                 be added to the beginning of the result unless  it  is  zero.
75                 For  all  floating-point  conversions  (e, E, f, g, and G) it
76                 guarantees that the result always has a decimal point.  For g
77                 and  G  conversions  it specifies that trailing zeroes should
78                 not be removed.
79
80   OPTIONAL FIELD WIDTH
81       The third portion of a conversion specifier is a decimal number  giving
82       a  minimum  field  width  for this conversion.  It is typically used to
83       make columns line up in tabular printouts.  If the  converted  argument
84       contains  fewer characters than the minimum field width then it will be
85       padded so that it is as wide as the minimum field width.  Padding  nor‐
86       mally  occurs by adding extra spaces on the left of the converted argu‐
87       ment, but the 0 and - flags may be used to specify padding with  zeroes
88       on  the left or with spaces on the right, respectively.  If the minimum
89       field width is specified as * rather than a number, then the next argu‐
90       ment  to the format command determines the minimum field width; it must
91       be an integer value.
92
93   OPTIONAL PRECISION/BOUND
94       The fourth portion of a conversion specifier is a precision, which con‐
95       sists  of a period followed by a number.  The number is used in differ‐
96       ent ways for different conversions.  For e, E,  and  f  conversions  it
97       specifies  the  number  of digits to appear to the right of the decimal
98       point.  For g and G conversions it specifies the total number of digits
99       to appear, including those on both sides of the decimal point (however,
100       trailing zeroes after the decimal point will still  be  omitted  unless
101       the  # flag has been specified).  For integer conversions, it specifies
102       a minimum number of digits to print (leading zeroes will  be  added  if
103       necessary).  For s conversions it specifies the maximum number of char‐
104       acters to be printed; if the string is longer than this then the trail‐
105       ing  characters  will be dropped.  If the precision is specified with *
106       rather than a number then the  next  argument  to  the  format  command
107       determines the precision; it must be a numeric string.
108
109   OPTIONAL SIZE MODIFIER
110       The fifth part of a conversion specifier is a size modifier, which must
111       be ll, h, or l.  If it is ll it specifies  that  an  integer  value  is
112       taken  without  truncation for conversion to a formatted substring.  If
113       it is h it specifies that an integer value is  truncated  to  a  16-bit
114       range  before converting.  This option is rarely useful.  If it is l it
115       specifies that the integer value is truncated to the same range as that
116       produced  by the wide() function of the expr command (at least a 64-bit
117       range).  If neither h nor l are present, the integer value is truncated
118       to  the  same  range as that produced by the int() function of the expr
119       command (at least a 32-bit range, but determined by the  value  of  the
120       wordSize element of the tcl_platform array).
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122   MANDATORY CONVERSION TYPE
123       The  last  thing  in  a conversion specifier is an alphabetic character
124       that determines what kind of conversion to perform.  The following con‐
125       version characters are currently supported:
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127       d         Convert integer to signed decimal string.
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129       u         Convert integer to unsigned decimal string.
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131       i         Convert integer to signed decimal string (equivalent to d).
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133       o         Convert integer to unsigned octal string.
134
135       x or X    Convert  integer to unsigned hexadecimal string, using digits
136                 “0123456789abcdef” for x and “0123456789ABCDEF” for X).
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138       b         Convert integer to unsigned binary string, using digits 0 and
139                 1.
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141       c         Convert integer to the Unicode character it represents.
142
143       s         No conversion; just insert string.
144
145       f         Convert  number  to signed decimal string of the form xx.yyy,
146                 where the number  of  y's  is  determined  by  the  precision
147                 (default: 6).  If the precision is 0 then no decimal point is
148                 output.
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150       e or E    Convert number to scientific notation in the form  x.yyyzz,
151                 where  the  number  of  y's  is  determined  by the precision
152                 (default: 6).  If the precision is 0 then no decimal point is
153                 output.   If  the E form is used then E is printed instead of
154                 e.
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156       g or G    If the exponent is less than -4 or greater than or  equal  to
157                 the  precision,  then convert number as for %e or %E.  Other‐
158                 wise convert as for %f.  Trailing zeroes and a trailing deci‐
159                 mal point are omitted.
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161       %         No conversion: just insert %.
162

DIFFERENCES FROM ANSI SPRINTF

164       The  behavior  of  the format command is the same as the ANSI C sprintf
165       procedure except for the following differences:
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167       [1]    Tcl guarantees that it will be working with UNICODE characters.
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169       [2]    %p and %n specifiers are not supported.
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171       [3]    For %c conversions the argument must be an integer value,  which
172              will then be converted to the corresponding character value.
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174       [4]    The  size  modifiers  are ignored when formatting floating-point
175              values.  The ll modifier has  no  sprintf  counterpart.   The  b
176              specifier has no sprintf counterpart.
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EXAMPLES

179       Convert  the  numeric  value  of  a  UNICODE character to the character
180       itself:
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182              set value 120
183              set char [format %c $value]
184
185       Convert the output of time into seconds to an accuracy of hundredths of
186       a second:
187
188              set us [lindex [time $someTclCode] 0]
189              puts [format "%.2f seconds to execute" [expr {$us / 1e6}]]
190
191       Create a packed X11 literal color specification:
192
193              # Each color-component should be in range (0..255)
194              set color [format "#%02x%02x%02x" $r $g $b]
195
196       Use  XPG3  format codes to allow reordering of fields (a technique that
197       is often used  in  localized  message  catalogs;  see  msgcat)  without
198       reordering the data values passed to format:
199
200              set fmt1 "Today, %d shares in %s were bought at $%.2f each"
201              puts [format $fmt1 123 "Global BigCorp" 19.37]
202
203              set fmt2 "Bought %2\$s equity ($%3$.2f x %1\$d) today"
204              puts [format $fmt2 123 "Global BigCorp" 19.37]
205
206       Print a small table of powers of three:
207
208              # Set up the column widths
209              set w1 5
210              set w2 10
211
212              # Make a nice header (with separator) for the table first
213              set sep +-[string repeat - $w1]-+-[string repeat - $w2]-+
214              puts $sep
215              puts [format "| %-*s | %-*s |" $w1 "Index" $w2 "Power"]
216              puts $sep
217
218              # Print the contents of the table
219              set p 1
220              for {set i 0} {$i<=20} {incr i} {
221                  puts [format "| %*d | %*ld |" $w1 $i $w2 $p]
222                  set p [expr {wide($p) * 3}]
223              }
224
225              # Finish off by printing the separator again
226              puts $sep
227

SEE ALSO

229       scan(n), sprintf(3), string(n)
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KEYWORDS

232       conversion specifier, format, sprintf, string, substitution
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236Tcl                                   8.1                            format(n)
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