awk 是一門非常優秀的文本處理工具，甚至可以上升作為一門程序設計語言。
它處理文本的速度是快得驚人的，現在很多基於shell 日志分析工具都可以用它完成。特點是設計簡單，速度表現很好，本文將介紹awk內置變量。
格式： awk [ -F re] [parameter...] ['pattern {action}' ] [-f progfile][in_file...]
一、內置變量
屬 性
說 明
$0
當前記錄行，代表一行記錄
$1~$n
當前記錄的第n個字段，字段間由FS分隔
FS
輸入字段分隔符，默認是空格
NF
當前記錄中的字段個數，就是有多少列，一般取最後一列字段
NR
已經讀出的記錄數，就是行號，從1開始
RS
輸入的記錄分隔符，默認為換行符
OFS
輸出字段分隔符，默是空格
ORS
輸出的記錄分隔符，默認為換行符
ARGC
命令行參數個數
ARGV
命令行參數數組
FILENAME
當前輸入文件的名字
IGNORECASE
如果為真，則進行忽略大小寫的匹配
ARGIND
當前被處理文件的ARGV標志符
CONVFMT
數字轉換格式 %.6g
ENVIRON
UNIX環境變量
ERRNO
UNIX系統錯誤消息
FIELDWIDTHS
輸入字段寬度的空白分隔字符串
FNR
當前記錄數
OFMT
數字的輸出格式 %.6g
RSTART
被匹配函數匹配的字符串首
RLENGTH
被匹配函數匹配的字符串長度
SUBSEP
\034
Built-in variables
Awk's built-in variables include the field variables: $1, $2, $3, and so on ($0 represents the entire record). They hold the text or values in the individual text-fields in a record.
Other variables include:
- NR: Keeps a current count of the number of input records.
- NF: Keeps a count of the number of fields in an input record. The last field in the input record can be designated by $NF.
- FS: Contains the "field separator" character used to divide fields on the input record. The default, "white space", includes any space and tab characters. FS can be reassigned to another character to change the field separator.
- RS: Stores the current "record separator" character. Since, by default, an input line is the input record, the default record separator character is a "newline".
- OFS: Stores the "output field separator", which separates the fields when Awk prints them. The default is a "space" character.
- ORS: Stores the "output record separator", which separates the output records when Awk prints them. The default is a "newline" character.
- OFMT: Stores the format for numeric output. The default format is "%.6g".
- FILENAME: Contains the name of the current input-file.
