AWK command in bash program

Question

here is my program:

for ((i=1;i<=300;i++)); do

  awk 'NR==$i{print}' file.dat > fileB.dat

done

the file.dat contains 300 lines that I want to save in different files, but the NR==$i doesn't work, nothing is printed.

I don't see what is wrong. Thank you

Sorry I am confused: Do you want to generate a single file with one line or 300 files with different lines? — Håkon Hægland
– Håkon Hægland, Commented Nov 29, 2013 at 14:06

dogbane · Accepted Answer · 2013-11-29 13:39:00Z

4

Single quotes prevent expansion, so $i is not expanded into a number. Use double quotes instead.

However, instead of invoking awk multiple times in a loop, it's more efficient to use a single awk like this:

awk 'NR<=300 {print > NR".dat"}' file.dat

This will write each line to a different file.

answered Nov 29, 2013 at 13:39

dogbane

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1 Comment

Ed Morton Over a year ago

+1 for the right answer but it needs to be print > (NR".dat") as it's ambiguous without the parens.

Fredrik Pihl · Accepted Answer · 2013-11-29 13:30:37Z

2

Try:

for i in {1..300}; do
    awk "NR==$i{print}" file.dat > fileB.dat
done

The single quote ', prevents the shell from expanding variables, in this case i.

answered Nov 29, 2013 at 13:30

Fredrik Pihl

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2 Comments

Fredrik Pihl Over a year ago

@EdMorton - well, dogbanes answer is much better, I just saw the error as a quoting issue and didn't think about it too much (I guess that's why he's a 70k rep user :-)

Ed Morton Over a year ago

The error is not a quoting issue though, it's a thinking error in mistaking awk for shell. By changing the quoting you can force the $i to expand but then you open yourself up to backslash hell because then $1 wouldn't mean the 1st field in the current record any more it'd mean the first positional parameter in the shell command so then you'd need to write \$1 just to get the normal, expected awk functionality. To get the value of a shell variable inside an awk script, you use -v i="$i" or similar. There are other awk problems introduced too and yes, the shell loop is wrong too.

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