**What is sorting?**

Sorting is taking a collection of things and putting them into some specific order. For example, sorting people by age, shoes by size, strings by length, planets by mass, numbers by value.

**What techniques are available within the Tcl language?**

   * '''[lsort]''' — takes a Tcl [list] argument and returns another list that is the sorted version of the input list. The other arguments determine exactly how the items in the list are to be ordered.

**What are other relevant pages on the wiki?**

   * [merge sorts]
   * [collation]
   * [custom sorting]
   * [How fast can we sort 5 elements]
   * [Sorted Lists]
   * [Topological sort]
   * [Simple Text Widget Sort]
   * [anytop]

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Frequently Asked Questions about sorting

   * How can I sort the contents of a file in tcl?

For sorting the lines of a file being read from standard input, and writing the result out to standard output, one can use the following one-liner:
  puts [join [lsort [split [read -nonewline stdin] \n]] \n]
Or in English: read in all the data to sort, split it into the list of units to be sorted, sort that list, join the sorted list back up in the external format, and write it out.

A complication is that, as [AMG] observed, at least on [Unix] most files end with a newline. The [split] and [join] above interpret newlines as line separators, not line terminators, so if `[[split … \n]]` is applied to something whose the last character is a newline, it thinks a zero-length line follows. This is fixed by using the -nonewline option of [read], which omits such a final newline. ''Not'' using the -nonewline option of [puts] furthermore normalises the output to end with a newline. (On [Windows], \n inside Tcl furthermore corresponds to CRLF outside by default, so there is typically no need to worry about line-end conventions.)

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