AWK - 孙愚

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这个词，那么这个表达式就是模式。操作由括在大括号中的一条或多条语句组成，语句之间用分号或者换行符隔开。模式不能括在大括号中，模式由包括在两个正斜杠之间的正则表达式、一个或多个操作符组成的表达式组成。 (...) Parentheses are used for grouping in regular expressions, as in arithmetic. They can be used to concatenate regular expressions containing the alternation operator. 匹配零个或者多个前导字符 ,{n,} ,{n,m} One or two numbers inside braces denote an interval expression. If there is one number in the braces, the preceding regexp is repeated n times. If there are two numbers separated by a comma, the preceding regexp is repeated n to m times. If there is one number followed by a comma, then the preceding regexp is repeated at least n times: Interval expressions were not traditionally available in awk. They were added as part of the POSIX standard to make awk and egrep consistent with each other. However, because old programs may use ‘{’ and ‘}’ in regexp constants, by default gawk does not match interval expressions in regexps. If either --posix or --re-interval are specified, then interval expressions are allowed in regexps. new programs that use ‘{’ and ‘}’ in regexp constants, it is good practice to always escape them with a backslash. Then the regexp constants are valid and work the way you want them to. the default case, gawk provides all the facilities of POSIX regexps and the previously described GNU regexp operators. GNU regexp operators described in Regexp Operators. However, interval expressions are not supported. POSIX regexps are supported; the GNU operators are not special (e.g., ‘/w’ matches a literal ‘w’). Interval expressions are allowed. Traditional Unix awk regexps are matched. The GNU operators are not special, interval expressions are not available, nor are the POSIX character classes ([[:alnum:]], etc.). Characters described by octal and hexadecimal escape sequences are treated literally, even if they represent regexp metacharacters. Also, gawk silently skips directories named on the command line. Allow interval expressions in regexps, even if --traditional has been provided. (--posix automatically enables interval expressions, so --re-interval is redundant when --posix is is used.) 变量以参数值的方式传递，且仅在使用它的函数中局部有效。函数使用的只是变量的副本。数组则通过地址或引用被传递，因此，可以在函数中直接修改数组的元素。函数中的变量只要不是从参数列表传来的，都视为全局变量。调用函数时，如果没有指定某个形参的值，该参数被初始化为空。

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