grammar
awk [options] [BEGIN] {program} [END] [file]
常用命令选项
-F fs 指定描绘一行中数据字段的文件分隔符 默认为空格
-f file 指定读取程序的文件名
-v var=value 定义awk程序中使用的变量和默认值
注意：awk 程序脚本由左大括号和右大括号定义。脚本命令必须放置在两个大括号之间。由于awk命令行假定脚本是单文本字符串，所以必须将脚本包
括在单引号内。
awk程序运行优先级是:
1)BEGIN: 在开始处理数据流之前执行，可选项
2)program: 如何处理数据流，必选项
3)END: 处理完数据流后执行，可选项awk basic usage
1. Field extraction: extracting a text and a data printout
Built-in variables related field
$ 0 represents the entire line of text
$ 1 represents the first line of text in a data field
$ 2 represents the second line of text in the data field
$ N represents the N lines of text data fields
$ NF represents the last line of text in the data field
# awk '{print $0}' t.txt
1 the quick brown fox jumps over the lazy dog.
2 the quick brown fox jumps over the lazy dog.
3 the quick brown fox jumps over the lazy dog.
4 the quick brown fox jumps over the lazy dog.
# awk '{print $1}' t.txt
1
2
3
4
# awk '{print $2}' t.txt
the
the
the
the
# awk '{print $3}' t.txt
quick
quick
quick
quick
# awk '{print $NF}' t.txt
dog.
dog.
dog.
dog.
2. How to print a line in a row and a column of it? Use the command NR
# awk 'NR==3{print $0}' t.txt
3 the quick brown fox jumps over the lazy dog.
# awk 'NR==3{print $1}' t.txt
3
# awk 'NR==3{print $2}' t.txt
the
3. If the data file is not separated by a space, such as the passwd is to: f separated, if necessary at this time can be used to specify delimiter -F
awk -F ":" 'NR == 1 {print $ 1, $ 3, $ 5}' / etc / passwd # prints the contents of the fifth row of the third line of the first row of the first column passwd file
root 0 root
If you want to change the output format of the above, it can be modified directly print the back part
# Awk -F ":" 'NR == 1 {print $ 1 "-" $ 3 "-" $ 5}' / etc / passwd # 3 between $ 1 $ 5 $ string directly increase
root-0-root
4. Print memory usage
# head -3 /proc/meminfo
MemTotal: 2035356 kB
MemFree: 1308408 kB
MemAvailable: 1472264 kB
# head -3 /proc/meminfo | awk 'NR==1{print $2}'
2035356