hello   world v1_echo   v1_diff   v1_comm  shell is easy!

hello world! v2_echo  v1_diff  easy shell!

1,2c1,2  < hello world  < v1_echo  ---  > hello world!  > v2_echo  4c4  < v1_comm  ---  > easy shell!

-v1_echo  +hello world!  +v2_echo  v1_diff  -v1_comm  +easy shell!  shell is easy!

 4c  easy shell!  .  1,2c  hello world!  v2_echo  .

Mandatory arguments to long options are mandatory for short options too.  --normal                                        output a normal diff (the default)  -q, --brief                                      report only when files differ  -s, --report-identical-files               report when two files are the same  -c, -C NUM, --context[=NUM]   output NUM (default 3) lines of copied context  -u, -U NUM, --unified[=NUM]     output NUM (default 3) lines of unified context  -e, --ed                                          output an ed script  -n, --rcs                                         output an RCS format diff  -y, --side-by-side                           output in two columns FILES 的格式可以是‘FILE1 FILE2'、‘DIR1 DIR2'、‘DIR FILE...'或 ‘FILE... DIR'。

 hello world               | hello world!  v1_echo                    | v2_echo  v1_diff                       v1_diff  v1_comm                   | easy shell!  shell is easy!               shell is easy!

用法：diff [选项]... FILES Compare FILES line by line. Mandatory arguments to long options are mandatory for short options too.       --normal                  output a normal diff (the default)   -q, --brief                   report only when files differ   -s, --report-identical-files  report when two files are the same   -c, -C NUM, --context[=NUM]   output NUM (default 3) lines of copied context   -u, -U NUM, --unified[=NUM]   output NUM (default 3) lines of unified context   -e, --ed                      output an ed script   -n, --rcs                     output an RCS format diff   -y, --side-by-side            output in two columns   -W, --width=NUM               output at most NUM (default 130) print columns       --left-column             output only the left column of common lines       --suppress-common-lines   do not output common lines   -p, --show-c-function         show which C function each change is in   -F, --show-function-line=RE   show the most recent line matching RE       --label LABEL             use LABEL instead of file name                                   (can be repeated)   -t, --expand-tabs             expand tabs to spaces in output   -T, --initial-tab             make tabs line up by prepending a tab       --tabsize=NUM             tab stops every NUM (default 8) print columns       --suppress-blank-empty    suppress space or tab before empty output lines   -l, --paginate                pass output through `pr' to paginate it   -r, --recursive                 recursively compare any subdirectories found   -N, --new-file                  treat absent files as empty       --unidirectional-new-file   treat absent first files as empty       --ignore-file-name-case     ignore case when comparing file names       --no-ignore-file-name-case  consider case when comparing file names   -x, --exclude=PAT               exclude files that match PAT   -X, --exclude-from=FILE         exclude files that match any pattern in FILE   -S, --starting-file=FILE        start with FILE when comparing directories       --from-file=FILE1           compare FILE1 to all operands;                                     FILE1 can be a directory       --to-file=FILE2             compare all operands to FILE2;                                     FILE2 can be a directory   -i, --ignore-case               ignore case differences in file contents   -E, --ignore-tab-expansion      ignore changes due to tab expansion   -Z, --ignore-trailing-space     ignore white space at line end   -b, --ignore-space-change       ignore changes in the amount of white space   -w, --ignore-all-space          ignore all white space   -B, --ignore-blank-lines        ignore changes whose lines are all blank   -I, --ignore-matching-lines=RE  ignore changes whose lines all match RE   -a, --text                      treat all files as text       --strip-trailing-cr         strip trailing carriage return on input   -D, --ifdef=NAME                output merged file with `#ifdef NAME' diffs       --GTYPE-group-format=GFMT   format GTYPE input groups with GFMT       --line-format=LFMT          format all input lines with LFMT       --LTYPE-line-format=LFMT    format LTYPE input lines with LFMT     These format options provide fine-grained control over the output       of diff, generalizing -D/--ifdef.     LTYPE 可以是‘old'、‘new'或‘unchanged'。GTYPE 可以是 LTYPE 的选择     或是‘changed'。     GFMT (only) may contain:       %<  lines from FILE1       %>  lines from FILE2       %=  lines common to FILE1 and FILE2       %[-][WIDTH][.[PREC]]{doxX}LETTER  printf-style spec for LETTER         LETTERs are as follows for new group, lower case for old group:           F  first line number           L  last line number           N  number of lines = L-F+1           E  F-1           M  L+1       %(A=B?T:E)  if A equals B then T else E     LFMT (only) may contain:       %L  contents of line       %l  contents of line, excluding any trailing newline       %[-][WIDTH][.[PREC]]{doxX}n  printf-style spec for input line number     Both GFMT and LFMT may contain:       %%  %       %c'C'  the single character C       %c'\OOO'  the character with octal code OOO       C    the character C (other characters represent themselves)   -d, --minimal            try hard to find a smaller set of changes       --horizon-lines=NUM  keep NUM lines of the common prefix and suffix       --speed-large-files  assume large files and many scattered small changes       --help               display this help and exit   -v, --version            output version information and exit   FILES 的格式可以是‘FILE1 FILE2'、‘DIR1 DIR2'、‘DIR FILE...'或       ‘FILE... DIR'。 If --from-file or --to-file is given, there are no restrictions on FILE(s). 如果 FILE 是‘-'，则由标准输入读取内容。 如果输入相同，则退出状态为 0；1 表示输入不同；2 表示有错误产生。