Should I trust AI

 Should I trust AI? So far no, sorry. 

I tested for the moment (May, 2025) most advanced model for programming and ask very simple question:

What is the meaning of this awk code: '{NF-=1;print}'

 

and get quite controversial answers (after correction from my side):

 

devstral-small-2505

Let's analyze the given awk script {NF-=1;print}:

Explanation:

In awk, the syntax {NF-=1;print} consists of two actions separated by a semicolon (;):

1. NF-=1:

   • NF: In awk, NF is an internal variable that stands for "Number of Fields." It represents the number of fields in the current record (line).
   • -= 1: This is a shorthand for NF = NF - 1. It decreases the value of NF by 1.

2. print:

   • This action prints the current line/record as-is.

What Happens:

When you run this script with input data, it performs the following steps on each line:

• Decreases the value of NF (Number of Fields) by 1.
• Prints the entire line.

However, modifying NF does not affect what gets printed. The print action in awk without any arguments will print the whole record as it is read from the input. Therefore, this script essentially prints each line of the input unchanged, with a side effect of reducing the value of NF, which might be useful if subsequent actions in the script rely on the modified NF.

Practical Example:

Suppose you have an input file called input.txt:

1 2 3
a b c d e
hello world

Running the awk script { NF-=1; print } on this file would produce:

awk '{ NF-=1; print }' input.txt

Output:

1 2 3
a b c d e
hello world

As you can see, each line is printed exactly as it appears in the input file.

Summary:

The given awk script {NF-=1;print} modifies NF by decrementing its value and then prints the current record (line) without any change. The modification of NF does not affect what gets printed, making this effectively equivalent to { print }.

 

And after my correction it give correct answer:

this is not true. the script: echo 1 2 3|awk '{NF-=1;print}' return result: 1 2

devstral-small-2505

You're correct, and I apologize for the oversight in my earlier explanation. Let's re-examine what happens with the awk command { NF -= 1; print }.

When you run:

echo "1 2 3" | awk '{ NF -= 1; print }'

The expected output is 1 2, which indeed indicates that the last field was removed. Here's why this happens and a more accurate explanation of what { NF-=1; print } actually does:

Explanation:

In awk, the following actions take place with { NF -= 1; print }:

1. NF -= 1:

   • NF: As before, NF is an internal variable representing the Number of Fields in the current record (line).
   • -= 1: This means "decrement NF by 1."

2. print:

   • Without any arguments, this action prints the entire line up to the modified value of NF.

Detailed Steps:

When you run:

echo "1 2 3" | awk '{ NF -= 1; print }'

• The input is processed as a single record: "1 2 3".
• Initially, NF equals 3 (since there are three fields).
• NF -= 1 changes it to 2 (NF now is 2).
• The print action prints the first two fields only up to this modified NF.

More Examples:

Let's explore a few more examples:

Example with Multiple Lines:

echo -e "1 2 3\n4 5 6" | awk '{ NF -= 1; print }'

Output:

1 2
4 5

Example with Different Field Separators:

echo "a,b,c,d,e" | awk 'BEGIN {FS=","} {NF-=1; print}'

Output:

a b c d

Summary:

The awk command { NF -= 1; print } effectively reduces the number of fields by one and prints only up to that new field count. This explains why in your example:

echo "1 2 3" | awk '{NF-=1;print}'

The output is:

1 2

Thank you for pointing out this correction!