Note about awk

Sometimes I use awk. However, since it's a little pace in a few months, every time I use it, I get "that? How do I use it?" I've done something to look up on the net, so I'll list the ones I often use.

You can use it just by knowing this

• print
• Variables \ $ 1 ~ \ $ ...
• Variable NR
• Variable NF
• Variable FS
• Variable FPAT
• STAR, END

Details of each item are as follows

Super basic

Suppose you have the following files:

sample.txt

No data1 data2 data3
1  101   102   103
2  201   202   203
3  301   302   303
4  401   402   403

Prepare an awk script as below

sample.awk

{
  print $1 " " $3
}

Specify sample.txt after specifying the script with the -f option from the terminal.

$ awk -f sample.awk sample.txt

The output is as follows.

No data2
1  102  
2  202  
3  302  
4  402  

Commentary

print

output

Variables $ 1 to $ ...

Contains each element in a line.

sample.txt

No data1 data2 data3 <----- $1 = "No", $2 = "data1", $3 = "data2", $4 = "data3" 
1  101   102   103
2  201   202   203
3  301   302   303
4  401   402   403

Get the sum for each column

Suppose you have the following files:

sample.txt

No data1 data2 data3
1  101   102   103
2  201   202   203
3  301   302   303
4  401   402   403

Prepare an awk script as below

sample.awk

{
    if(NR > 1){
        sum1 += $2;
        sum2 += $3;
        sum3 += $4;
    }
}

END {
    print sum1 " " sum2 " " sum3;
}

Specify sample.txt after specifying the script with the -f option from the terminal.

$ awk -f sample.awk sample.txt

The output is as follows.

1004 1008 1012

Commentary

Variable NR

Current number of lines. In this example, the first line is the title, so it is ignored.

END

End processing. Here, the total value is output.

I want to get the total for each row.

Suppose you have the following files:

sample.txt

No data1 data2 data3
1  101   102   103    <----- 101 + 102 +I want to find 103.
2  201   202   203
3  301   302   303
4  401   402   403

Prepare an awk script as below

sample.awk

{
    sum = 0;
    for(i=2; i<=NF; i++) {
        sum += $i;
    }
    print sum;
}

Specify sample.txt after specifying the script with the -f option from the terminal.

$ awk -f sample.awk sample.txt

The output is as follows.

0
306
606
906
1206

Commentary

Variable NF

Contains the number of elements in each line.

File delimiters are commas instead of spaces

Suppose you have the following files:

sample.txt

No,data1,data2,data3
1,101,102,103
2,201,202,203
3,301,302,303
4,401,402,403

Prepare an awk script as below

sample.awk

BEGIN {
    FS = ",";
}

{
  print $1 " " $3
}

Specify sample.txt after specifying the script with the -f option from the terminal.

$ awk -f sample.awk sample.txt

The output is as follows.

No data2
1 102
2 202
3 302
4 402

Commentary

Variable FS

Separation position of each element. The default is blank.

START

You can write the start process.

File delimiters are commas, not spaces. Also, each element contains a comma.

sample.txt

No,data1,data2,data3
1,101,"102,101",103
2,201,202,203
3,301,"302,101",303
4,401,402,403

Prepare an awk script as below

sample.awk

BEGIN {
    FPAT = "([^,]+)|(\"[^\"]+\")"
}

{
    print $1 " " $3
}

Specify sample.txt after specifying the script with the -f option from the terminal.

$ awk -f sample.awk sample.txt

The output is as follows.

No data2
1 "102,101"
2 202
3 "302,101"
4 402

Commentary

Variable FPAT

Each element can be described by a regular expression.