Master pattern matching with grep -E使用 grep -E 掌握模式匹配
A Regular Expression (regex) is a sequence of characters that defines a search pattern. It's like a super-powered "find" function that can match complex patterns, not just exact text.
正则表达式（regex）是定义搜索模式的字符序列。它就像一个超级"查找"功能，可以匹配复杂的模式，而不仅仅是精确的文本。
🔍 Simple Analogy - Normal search finds "cat", regex finds "any word starting with c, ending with t"
🔍 简单类比 - 普通搜索找"张三"，正则搜索找"所有姓张的人"
grep -E uses extended regular expressions, which gives us more powerful features without needing to escape special characters.
grep -E 使用扩展正则表达式，提供更强大的功能，无需转义特殊字符。
Square brackets match any one character from the set.
方括号匹配集合中的任意一个字符。
| Pattern模式 | Meaning含义 | Matches匹配 | Doesn't Match不匹配 |
|---|---|---|---|
[aeiou] |
Any vowel任意元音 | a, e, i, o, u | b, c, d |
[a-z] |
Any lowercase letter任意小写字母 | a, b, c, ... z | A, B, 1, 2 |
[A-Z] |
Any uppercase letter任意大写字母 | A, B, C, ... Z | a, b, 1, 2 |
[0-9] |
Any digit任意数字 | 0, 1, 2, ... 9 | a, b, c |
With ^ as the first character, it matches any character NOT in the set.
当 ^ 作为第一个字符时，它匹配不在集合中的任意字符。
| Pattern模式 | Meaning含义 | Matches匹配 |
|---|---|---|
[^aeiou] |
Any non-vowel (consonants, digits, etc.)任意非元音（辅音、数字等） | b, c, d, 1, 2, ! |
[^ ] |
Any non-space character任意非空格字符 | a, B, 1, ! |
Quantifiers specify how many times the previous element can appear.
量词指定前面的元素可以出现多少次。
| Symbol符号 | Meaning含义 | Pattern模式 | Matches匹配 |
|---|---|---|---|
* |
0 or more times0次或多次 | ab*c |
ac, abc, abbc, abbbc |
+ |
1 or more times1次或多次 | ab+c |
abc, abbc, abbbc (not ac) |
? |
0 or 1 time (optional)0次或1次（可选） | colou?r |
color, colour |
{n} |
Exactly n times正好n次 | [aeiou]{4} |
eeee, auio, euou |
{n,m} |
Between n and m timesn到m次 | a{2,4} |
aa, aaa, aaaa |
⭐ Remember: * = "zero or more" (can be empty), + = "one or more" (must have at least one)
⭐ 记住: * = "零或多个"（可以是空的），+ = "一个或多个"（必须至少有一个）
| Symbol符号 | Meaning含义 | Pattern模式 | Matches匹配 |
|---|---|---|---|
. |
Any single character任意单个字符 | c.t |
cat, cot, cut, c5t |
.* |
Any characters, any times任意字符，任意次数 | a.*e |
ae, apple, anyone |
^ |
Start of line行首 | ^Hello |
"Hello world" |
$ |
End of line行尾 | end$ |
"the end" |
💡 Tip: Use ^pattern$ to match the entire line, not just part of it!
💡 提示: 使用 ^pattern$ 来匹配整行，而不仅仅是部分！
\b matches the position between a word character and a non-word character (like spaces, punctuation, start/end of line).
\b 匹配单词字符和非单词字符（如空格、标点、行首/尾）之间的位置。
| Pattern模式 | Matches匹配 | Doesn't Match不匹配 |
|---|---|---|
cat\b |
"cat", "cat.", "a cat" | "category", "concat" |
\bcat |
"cat", "a cat" | "concat", "bobcat" |
\bcat\b |
"cat" (whole word only) | "category", "bobcat" |
Use | to match either the pattern before or after it.
使用 | 匹配前面或后面的模式。
Parentheses group patterns together, often used with ? for optional parts.
括号将模式组合在一起，通常与 ? 一起使用表示可选部分。
💡 Pattern: (pattern)? = "this part is optional"
💡 模式: (pattern)? = "这部分是可选的"
| Symbol符号 | Meaning含义 | Example示例 |
|---|---|---|
abc | Literal match字面匹配 | lmn → calmness |
[abc] | Any one of其中任意一个 | [aeiou] → vowel |
[^abc] | NOT any of不是其中任意一个 | [^aeiou] → consonant |
. | Any character任意字符 | a.c → abc, a1c |
* | 0 or more0次或多次 | ab*c → ac, abc |
+ | 1 or more1次或多次 | ab+c → abc, abbc |
? | Optional (0 or 1)可选（0或1次） | colou?r → color |
{n} | Exactly n正好n次 | [aeiou]{4} |
\b | Word boundary单词边界 | \bcat\b |
^ | Line start行首 | ^Hello |
$ | Line end行尾 | end$ |
| | OR或者 | cat|dog |
( ) | Grouping分组 | (ab)+ |
❌ Wrong: *abc* - * at the start has nothing to repeat!
❌ 错误: *abc* - * 在开头没有东西可以重复！
❌ Wrong: .* is too greedy - it matches too much!
❌ 错误: .* 太贪婪 - 它匹配太多了！
❌ Wrong: Forgetting ^ and $ when you need to match the entire line
❌ 错误: 当需要匹配整行时忘记 ^ 和 $
⚠️ Remember: Case matters! Use [AEIOUaeiou] for both cases, or use grep -i
⚠️ 记住: 大小写很重要！使用 [AEIOUaeiou] 匹配两种情况，或使用 grep -i