SORT(1L)

NAME
sort - sort lines of text files

SYNOPSIS
sort [-cmus] [-t separator] [-o output-file] [-T tempdir] [-bdfiMnr] [+POS1 [-POS2]] [-k POS1[,POS2]] [file...]

DESCRIPTION
This manual page documents the GNU version of sort. sort sorts, merges, or compares all the lines from the given files, or the standard input if no files are given. A file name of `-' means standard input. By default, sort writes the results to the standard output.

sort has three modes of operation: sort (the default), merge, and check for sortedness. The following options change the operation mode:

-c  Check whether the given files are already sorted: if they are not all sorted, print an error message and exit with a status of 1.

-m  Merge the given files by sorting them as a group. Each input file should already be individually sorted. It always works to sort instead of merge; merging is provided because it is faster, in the case where it works.

A pair of lines is compared as follows: if any key fields have been specified, sort compares each pair of fields, in the order specified on the command line, according to the associated ordering options, until a difference is found or no fields are left.

If any of the global options Mbdfinr are given but no key fields are specified, sort compares the entire lines according to the global options.

Finally, as a last resort when all keys compare equal (or if no ordering options were specified at all), sort compares the lines byte by byte in machine collating sequence. The last resort comparison honors the -r global option. The -s (stable) option disables this last-resort comparison so that lines in which all fields compare equal are left in their original relative order. If no fields or global options are specified, -s has no effect.

GNU sort has no limits on input line length or restrictions on bytes allowed within lines. In addition, if the final byte of an input file is not a newline, GNU sort silently supplies one.

If the environment variable TMPDIR is set, sort uses it as the directory in which to put temporary files instead of the default, /tmp. The -T tempdir option is another way to select the directory for temporary files; it overrides the environment variable.

The following options affect the ordering of output lines. They may be specified globally or as part of a specific key field. If no key fields are specified, global options apply to comparison of entire lines; otherwise the global options are inherited by key fields that do not specify any special options of their own.

-b  Ignore leading blanks when finding sort keys in each line.

-d  Sort in `phone directory' order: ignore all characters except letters, digits and blanks when sorting.

-f  Fold lower case characters into the equivalent upper case characters when sorting so that, for example, `b' is sorted the same way `B' is.

-i  Ignore characters outside the ASCII range 040-0176 octal (inclusive) when sorting.

-M  An initial string, consisting of any amount of white space, followed by three letters abbreviating a month name, is folded to UPPER case and compared in the order `JAN' < `FEB' < ... < `DEC.' Invalid names compare low to valid names.

-n  Compare according to arithmetic value an initial numeric string consisting of optional white space, an optional - sign, and zero or more digits, optionally followed by a decimal point and zero or more digits.

-r  Reverse the result of comparison, so that lines with greater key values appear earlier in the output instead of later.

Other options are:

-o output-file
    Write output to output-file instead of to the standard output. If output-file is one of the input files, sort copies it to a temporary file before sorting and writing the output to output-file.

-t separator
    Use character separator as the field separator when finding the sort keys in each line. By default, fields are separated by the empty string between a non-whitespace character and a whitespace character. That is to say, given the input line ` foo bar', sort breaks it into fields ` foo' and ` bar'. The field separator is not considered to be part of either the field preceding or the field following it.

-u  For the default case or the -m option, only output the first of a sequence of lines that compare equal. For the -c option, check that no pair of consecutive lines compares equal.

+POS1 [-POS2]
    Specify a field within each line to use as a sorting key. The field consists of the portion of the line starting at POS1 and up to (but not including) POS2 (or to the end of the line if POS2 is not given). The fields and character positions are numbered starting with 0.

-k POS1[,POS2]
    An alternate syntax for specifying sorting keys. The fields and character positions are numbered starting with 1.

A position has the form f.c, where f is the number of the field to use and c is the number of the first character from the beginning of the field (for +pos) or from the end of the previous field (for -pos). The .c part of a position may be omitted in which case it is taken to be the first character in the field. If the -b option has been given, the .c part of a field specification is counted from the first nonblank character of the field (for +pos) or from the first nonblank character following the previous field (for -pos).

A +pos or -pos argument may also have any of the option letters Mbdfinr appended to it, in which case the global ordering options are not used for that particular field. The -b option may be independently attached to either or both of the +pos and -pos parts of a field specification, and if it is inherited from the global options it will be attached to both. If a -n or -M option is used, thus implying a -b option, the -b option is taken to apply to both the +pos and the -pos parts of a key specification. Keys may span multiple fields.

COMPATIBILITY

Historical (BSD and System V) implementations of sort have differed in their interpretation of some options, particularly -b, -f, and -n. GNU sort follows the POSIX behavior, which is usually (but not always!) like the System V behavior. According to POSIX -n no longer implies -b. For consistency, -M has been changed in the same way. This may affect the meaning of character positions in field specifications in obscure cases. If this bites you the fix is to add an explicit -b.

BUGS
The different meaning of field numbers depending on whether -k is used is confusing. It's all POSIX's fault!