[dbohdan] 2014-06-14: I wanted to have 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.
======
<<categories>>String Processing