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