diff命令适用于比较多个文本本件的差异
diff命令格式为：“wc [参数] 文件”
diff参数
--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
用例：
diff -c a.log b.log
