有时候经常使用sort来排序，需要预处理把需要排序的field语言在最前面。实际上这是
完全没有必要的，利用-k参数就足够了。
比如sort all
1 4
2 3
3 2
4 1
5 0
如果sort -k 2的话，那么执行结果就是
5 0
4 1
3 2
2 3
1 4
它按照第二个域进行排序。
如下为man sort：
Usage: sort [OPTION]… [FILE]…
Write sorted concatenation of all FILE(s) to standard output.
Ordering options:
Mandatory arguments to long options are mandatory for short options too.
-b, -ignore-leading-blanks ignore leading blanks
-d, -dictionary-order consider only blanks and alphanumeric characters
-f, -ignore-case fold lower case to upper case characters
-g, -general-numeric-sort compare according to general numerical value
-i, -ignore-nonprinting consider only printable characters
-M, -month-sort compare (unknown) < `JAN’ < … < `DEC’
-n, -numeric-sort compare according to string numerical value
-r, -reverse reverse the result of comparisons
Other options:
-c, -check check whether input is sorted; do not sort
-k, -key=POS1[,POS2] start a key at POS1, end it at POS 2 (origin 1)
-m, -merge merge already sorted files; do not sort
-o, -output=FILE write result to FILE instead of standard output
-s, -stable stabilize sort by disabling last-resort comparison
-S, -buffer-size=SIZE use SIZE for main memory buffer
-t, -field-separator=SEP use SEP instead of non-blank to blank transition
-T, -temporary-directory=DIR use DIR for temporaries, not $TMPDIR or /tmp;
multiple options specify multiple directories
-u, -unique with -c, check for strict ordering;
without -c, output only the first of an equal run
-z, -zero-terminated end lines with 0 byte, not newline
-help display this help and exit
-version output version information and exit
POS is F[.C][OPTS], where F is the field number and C the character position
in the field. OPTS is one or more single-letter ordering options, which
override global ordering options for that key. If no key is given, use the
entire line as the key.
SIZE may be followed by the following multiplicative suffixes:
% 1% of memory, b 1, K 1024 (default), and so on for M, G, T, P, E, Z, Y.
With no FILE, or when FILE is -, read standard input.