format - Format a string in the style of sprintf
format formatString ?arg arg ...?
This command generates a formatted string in the same way as the ANSI C sprintf procedure (it uses sprintf in its implementation). FormatString indicates how to format the result, using % conversion specifiers as in sprintf, and the additional arguments, if any, provide values to be substituted into the result. The return value from format is the formatted string.
More at: http://purl.org/tcl/home/man/tcl8.4/TclCmd/format.htm
Tips and Tricks with format
You can use [format] to produce unsigned integers for display (but don't reckon with them - for expr they're still signed!):
% format %u -1 4294967295
See floating-point formatting for discussion on how to write format strings to handle floats...
To make numbers look nice:
set fah [format "%0.2f" [expr $temperature_cel * 9 / 5 + 32]]
Color formatting:
set color [format #%02x%02x%02x $r $g $b]
A limited formatting of decimals to characters is available in other languages, e.g. CHR() in Basic. If you use that more often, here's a cute shortcut:
interp alias {} chr {} format %c
% set a [chr 49][chr 48]
10See Narrow formatting for short rendering of big integers, with powers of 1024:
% fixform 12345678 11.7M
this method should get format string and explain the format structure. this is a fast scatch.
proc explainFormat {formatStr} {
set index 1
foreach frm [split $formatstr "%"] {
set extra ""
set size 0
regexp {([0-9]+)([duioxXcsfegG])(.*)} $frm => size type extra
if {$size==0} {
set size [string length $frm]
} else {
set frm "%$size$type"
set size [string trimleft $size 0]
}
for {set i 0} {$i<2} {incr i} {
set newIndex [expr {$size +$index -1}]
puts "$index-$newIndex '$frm'"
set index [expr {$newIndex +1}]
if {$extra==""} {
break
} else {
set frm $extra
set size [string length $extra]
}
}
}
}%explainFormat hello%02s000%3d
1-5 'hello'
6-7 '%02s'
8-10 '000'
11-13 '%3d'
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