用途
按行比较文件差异，也可以比较目录
用法
diff [OPTION]... FILES
常用选项
-i --ignore-case
忽略大小写
--ignore-file-name-case
忽略文件名大小写
--no-ignore-file-name-case
文件名区分大小写
-E --ignore-tab-expansion
忽略tab字符
-b --ignore-space-change
忽略空格
-w --ignore-all-space
忽略所有空格
-B --ignore-blank-lines
忽略空白行
-I RE --ignore-matching-lines=RE
过滤匹配的行
--strip-trailing-cr
去掉行尾回车符
-a --text
所有文件内容当做文本
-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.)
--label LABEL
使用LABEL代替文件名
-p --show-c-function
显示差异行所在文件
-F RE --show-function-line=RE
(Show the most recent line matching RE.)
-q --brief
直接输出结果是否有差异
-e --ed
(Output an ed script.)
--normal
(Output a normal diff.)
-n --rcs
(Output an RCS format diff.)
-y --side-by-side
同时输出2个文件的内容，对照显示
-W NUM --width=NUM
(Output at most NUM (default 130) print columns.)
--left-column
左边输出完整内容，右边只输出差异
--suppress-common-lines
只输出差异行
-D NAME --ifdef=NAME
(Output merged file to show ‘#ifdef NAME’ diffs.)
--GTYPE-group-format=GFMT
(Similar, but format GTYPE input groups with GFMT.)
(GTYPE is LTYPE or ‘changed’.)
--line-format=LFMT
(Similar, but format all input lines with LFMT.)
--LTYPE-line-format=LFMT
(Similar, but format LTYPE input lines with LFMT.)
(LTYPE is ‘old’, ‘new’, or ‘unchanged’.)
-l --paginate
分页显示
-t --expand-tabs
输出时，tab字符换成空格
-T --initial-tab
(Make tabs line up by prepending a tab.)
-r --recursive
(Recursively compare any subdirectories found.)
-N --new-file
(Treat absent files as empty.)
--unidirectional-new-file
(Treat absent first files as empty.)
-s --report-identical-files
(Report when two files are the same.)
-x PAT --exclude=PAT
(Exclude files that match PAT.)
-X FILE --exclude-from=FILE
(Exclude files that match any pattern in FILE.)
-S FILE --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.)
--horizon-lines=NUM
(Keep NUM lines of the common prefix and suffix.)
-d --minimal
(Try hard to find a smaller set of changes.)
--speed-large-files
(Assume large files and many scattered small changes.)
-v --version
输出程序版本信息
--help
显示帮助信息
实践
1 比较2个文件
# 显示所有
diff -y dir1/friend.php friend.php
# 只显示差异
diff -y --suppress-common-lines dir1/friend.php friend.php
# 只显示左边完整内容，右边只显示差异内容
diff -y --left-column dir1/friend.php friend.php
擦参考资料
【1】man diff