awk array next issue

Shell Programming and Scripting
1

Hi,

Here's an example of what I my issue, a file list.txt, which looks like:

a
b
c
d
e

I have been trying to use the following code to simply print the list using awk and next:

awk 'FNR==NR{a[$1]=$1;next}{print a[$1]}' list.txt

this give no output, even though I would expect it to type out the list. Removing the next command works fine:

awk 'FNR==NR{a[$1]=$1}{print a[$1]}' list.txt

What am I missing? Why doesn't the first code work?

2

next means it jumps to the end of the script, skipping the following program code.
next is useful with two input files.
The first one (where FNR==NR is true) reads into the array, and the following code is skipped.
During the second file (where FNR!=NR i.e. skips the following {block} ) it runs the code following the skipped {block} .

3

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4

To clarify what MadeInGermany wrote:
With that particular awk construct (your first example), you need to specify two input files, not one. With one file, the print part never gets executed.

Also, there seems to be a typo, NFS should be FNR .

1 Like
5

Thanks for the hint, I have corrected my post.

6

Hello hexy,

Adding to Made in Germany's point here too. next is useful for another thing too. So let's say we have many conditions in our program(which are NOT dependent on each other), we could use next and could tell awk NOT to go further checks and could save some cycles there.

Thanks,
R. Singh