ruler
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ruler
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	#!/usr/bin/env tclsh8.6

	set DEFAULT_LEN 80

	proc spaces_for_dozen {n} {
	string repeat " " [expr 10 - [string length $n]]
	}

	proc ruler {len} {
	set i 0
	set tens [expr $len / 10]

	set line_units ""
	set line_tens ""

	# First, build our ruler string by appending groups of 10 digits
	while {$i < $tens} {
	incr i

	append line_units "1234567890"

	append line_tens [spaces_for_dozen $i]
	append line_tens $i
	}

	# Then, adds units for our last group if needed
	set remaining_units [expr $len % 10]
	for {set i 1} {$i <= $remaining_units} {incr i} {
	append line_units $i
	}

	# Prints the lines
	join [list $line_units $line_tens] "\n"
	}

	#
	# Parses arguments
	#

	proc usage {} {
	set command [file tail [info script]]

	puts stderr "Usage: $command \[len\]"
	puts stderr "Print a ruler of specified length."
	}

	if {$argc == 0} {
	set len $DEFAULT_LEN
	} elseif {$argc == 1} {
	set len $argv

	if {![string is integer $len]} {
	usage
	exit 2
	}
	} {
	usage
	exit 1
	}

	#
	# Procedural part
	#

	puts [ruler $len]