Hanging bash loop script?

Question

varrr=0

while read line
do
    if [ $line -gt 500 -a $line -le 600 ]; then    # for lines 501-600
        echo $line >> 'file_out_${varrr}.ubi'
    fi
done << 'file_in_${varrr}.ubi'

file_in_${varrr}.ubi is a text file with around 1000 lines. I want to print lines 501-600 to new file.

Running this code leaves my Ubuntu terminal with a > symbol on a new line, as if I need to type another command to finish the loop. I can' figure out what is wrong with this loop though. Seems like it's complete. See any mistakes I've made? Thanks.

gniourf_gniourf · Accepted Answer · 2013-09-13 10:33:34Z

1

I'm only going to answer your specific question: it's because you used a heredoc << symbol, instead of a redirection <. Your last line should read:

done < 'file_in_${varrr}.ubi'

(observe the single <).

But then you'll realize that you have some quoting problems. So, your last line should read:

done < "file_in_${varrr}.ubi"

(observe the double quotes ").

Similarly, watch out your quotings in line 6. You should have this instead:

echo "$line" >> "file_out_${varrr}.ubi"

(double quotes " for file_out_${varrr}.ubi).

But then, this will not behave as you expect... Maybe this will do:

varrr=0
linenb=0
while IFS= read -r line; do
    ((++linenb))
    if ((linenb>500 && linenb<=600)); then    # for lines 501-600
        echo "$line" >> "file_out_${varrr}.ubi"
    fi
done < "file_in_${varrr}.ubi"

Hope this helps!

edited Sep 13, 2013 at 10:33

answered Sep 13, 2013 at 10:27

gniourf_gniourf

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1 Comment

brastein Over a year ago

Thanks, yeah I needed a counter, as well as the quotation marks you pointed out.

fedorqui · Accepted Answer · 2013-09-13 09:59:30Z

1

If you just want to print lines from 501 to 600, why don't you use the following?

awk 'NR>=501 && NR<=600' file_in > file_out

awk 'NR==n' myfile prints the line n of the file myfile. Then, you can use ranges as I writted above.

answered Sep 13, 2013 at 9:59

fedorqui

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brastein Over a year ago

Thanks for the tip, I ended up using awk for this :)

konsolebox · Accepted Answer · 2013-09-13 10:32:37Z

1

You can simply use sed. It's the simplest tool for it and is cleaner and faster than a while loop with tests.

varrr=0
sed -n 501,600p "file_in_${varrr}.ubi" >> "file_out_${varrr}.ubi"

Or

varrr=0
sed -n 501,600p "file_in_${varrr}.ubi" > "file_out_${varrr}.ubi"

If you want to override existing data.

The mistake in your loop by the way is because you're not using a counter and comparing your line number by the line itself instead.

varrr=0
counter=0
while read line; do
    (( ++counter ))
    [[ counter -gt 500 && counter -le 600 ]] && echo "$line"
done < "file_in_${varrr}.ubi" > "file_out_${varrr}.ubi"

Noticeably you need to use < for input not << and place your variables around double quotes not single quotes.

edited Sep 13, 2013 at 10:32

answered Sep 13, 2013 at 10:23

konsolebox

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1 Comment

brastein Over a year ago

Thanks, I'm new to bash and you helped me understand I need a counter. Totally needed. But I'll look into using sed or awk instead.

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