sort 排序
# sort --help
-b, --ignore-leading-blanks ignore leading blanks //忽略空白行
-d, --dictionary-order consider only blanks and alphanumeric characters//字典顺序
-f, --ignore-case fold lower case to upper case characters//忽略大小写
-g, --general-numeric-sort compare according to general numerical value//通用数值排序
-i, --ignore-nonprinting consider only printable characters//忽略非打印
-M, --month-sort compare (unknown) < `JAN' < ... < `DEC'//按月排序
-n, --numeric-sort compare according to string numerical value//数字排序
-r, --reverse reverse the result of comparisons//降序
-c, --check check whether input is sorted; do not sort
-k, --key=POS1[,POS2] start a key at POS1, end it at POS2 (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
