[one day learning awk] use of built-in variables

1. ARGC、ARGV

ARGC Represents the number of variables （Argument Count）

ARGV Represents variable content （Argument Variable）

awk 'BEGIN{
    for (i = 0; i < ARGC; ++i){
        printf "args[%d]=%s\n", i, ARGV[i]
    }

}' arg0, arg1, arg2, arg3, arg4

We found that ,awk Is the first parameter , Other parameters are from 1 At the beginning ：

Use here ARGC A cycle was carried out ,ARGV Is an array , Traversable .

2. Format symbol CONVFMT

awk 'BEGIN{print "FORMAT=", CONVFMT}'

3. environment variable ENVIRON

Use ENVIRON Get environment variables , The values of specific environment variables can be executed env see

awk 'BEGIN{print ENVIRON["USER"]}'

 

4. Get the file name FILENAME

awk 'END{print FILENAME}' marks.txt

 

 

5. NF、NR、FNR

NF A number of columns （Number Field）

NR Number of lines （Number Row）

FNR And NR similar , When multiple files , Different documents are numbered separately

Print the number of columns and data ：

 

Print line numbers and data ：

 

6. FS、RS、OFS、ORS、OFMT

FS Indicates the input column split symbol （Field Split）, Default is space

 RS Indicates the input newline character （Row Split）, The default is \n

OFS Is the output column split symbol （Field Split）, Default is space  

ORS Indicates the output newline character （Row Split）, The default is \n

 OFMT Presentation output format , Default %.6g

 

7. RSTART And RLENGTH

RSTART Indicates the position of the first match

RLENGTH Indicates the length of the first match

8. $n What column do you want to get

 

9. Wrong content ERRNO