[dbohdan] 2014-06-14: I wanted to have a multiline string help message indented to the level of the rest of the code. The following procedure unindents it appropriately but keeps the relative indentation.

======
# Trim indentation in multiline quoted text based on the first line's.
proc trim-indentation {msg} {
    set msgLines [split $msg \n]
    if {[lindex $msgLines 0] eq {}} {
        shift msgLines
    }

    set firstLine [lindex $msgLines 0]

    set indent [
        expr {
            [string length $firstLine] -
            [string length [string trimleft $firstLine]]
        }
    ]

    return [
        join [
            struct::list mapfor x $msgLines {string range $x $indent end}
        ] \n
    ]
}
======

***Use example***

======
[...]
    if {[llength $args] == 0} {
        # Print help
        puts -nonewline [
            trim-indentation {
                Command pipelines for interactive programming.

                usage:
                    |> cmd1 |> cmd2 _ |> cmd3 #0 ?-debug?
                or
                    |> { cmd1 |> cmd2 $_ |> cmd3 $pipe(0) } ?-debug?

                See http://wiki.tcl.tk/17419 for more.
            }
            return
        ]
        # End help
    }
[...]
======

***Output***

======
Command pipelines for interactive programming.

usage:
    |> cmd1 |> cmd2 _ |> cmd3 #0 ?-debug?
or
    |> { cmd1 |> cmd2 $_ |> cmd3 $pipe(0) } ?-debug?

See http://wiki.tcl.tk/17419 for more.
======



[PYK] 2014-06-14: What does `shift` do?  This implementation uses the
simplistic method of counting the number of characters trimmed from the first
line, and fails for cases where the first line is more indented than other
lines.  To do the job right, see [textutil%|%textutil::undent]. Also, as of
[Tcl 8.6%|%8.6], `[lmap]` is the [Tcl Commands%|%built-in] replacement for
`[struct::list] mapfor]`.


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