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Top Forums UNIX for Dummies Questions & Answers Explanation of the sort command Post 302758741 by bakunin on Sunday 20th of January 2013 05:39:36 PM
Old 01-20-2013
Quote:
Originally Posted by jimbojames
I was confused with what the
Code:
4,4n

was doing, but your explanation has helped with this, although I still don't understand what the 4 before the comma is doing.
"sort" interprets lines as "fields" being delimited by "delimiters". Per default this delimiter is whitespace.

Per default "sort" sorts on field 1, then on field 2, then field 3 and so on until the end of the line. Lines with equal values of field 1 will be sorted on the contents of field 2, lines with equal fields 1 & 2 sorted on field 3, etc. If you want another field or part of it) as the primary key you will have to use the "-k" option and a field number. But this leaves the question, how lines with equal sort keys should be handled.

Per default sort will use the fields starting with field 1 as secondary sort key in this case:

Code:
sort -k4

will produce the sort order: f4, f1, f2, f3, f4, ....

By defining, where the key should end you can change this default behavior:

Code:
sort -k4,4

Sorting occurs exclusively on field 4, because the ",4" says the ending of the sort key is field 4.

The man page of sort should explain this in greater detail.

I hope this helps.

bakunin
 

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SORT(1) 						      General Commands Manual							   SORT(1)

NAME
sort - sort a file of ASCII lines SYNOPSIS
sort [-bcdfimnru] [-tc] [-o name] [+pos1] [-pos2] file ... OPTIONS
-b Skip leading blanks when making comparisons -c Check to see if a file is sorted -d Dictionary order: ignore punctuation -f Fold upper case onto lower case -i Ignore nonASCII characters -m Merge presorted files -n Numeric sort order -o Next argument is output file -r Reverse the sort order -t Following character is field separator -u Unique mode (delete duplicate lines) EXAMPLES
sort -nr file # Sort keys numerically, reversed sort +2 -4 file # Sort using fields 2 and 3 as key sort +2 -t: -o out # Field separator is : sort +.3 -.6 # Characters 3 through 5 form the key DESCRIPTION
Sort sorts one or more files. If no files are specified, stdin is sorted. Output is written on standard output, unless -o is specified. The options +pos1 -pos2 use only fields pos1 up to but not including pos2 as the sort key, where a field is a string of characters delim- ited by spaces and tabs, unless a different field delimiter is specified with -t. Both pos1 and pos2 have the form m.n where m tells the number of fields and n tells the number of characters. Either m or n may be omitted. SEE ALSO
comm(1), grep(1), uniq(1). SORT(1)
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