-e
严格来说是用于指示您要匹配的模式的标志。-E
控制是否需要转义某些特殊字符。
man grep
进一步说明-E
:
Basic vs Extended Regular Expressions
In basic regular expressions the meta-characters ?, +, {, |, (, and ) lose their special meaning; instead use the backslashed versions \?, \+, \{, \|, \(, and \).
Traditional egrep did not support the { meta-character, and some egrep implementations support \{ instead, so portable scripts should avoid { in grep -E patterns and should use [{] to match a
literal {.
GNU grep -E attempts to support traditional usage by assuming that { is not special if it would be the start of an invalid interval specification. For example, the command grep -E '{1' searches for
the two-character string {1 instead of reporting a syntax error in the regular expression. POSIX.2 allows this behavior as an extension, but portable scripts should avoid it.