CODEWITHSUNDEEP
bashloopssed
Matt H
Matt H

Reputation: 91

In a Bash script, loop through lines in a file and modify them?

I'm just learning Bash scripting, and I couldn't quite find an answer on here that worked for me, so here's what I'm trying to do...

I've got file list.txt with contents like this..

group: 43  [message]
group: 312  [message]
group: 501210  [message]

In a bash script, I'm trying to loop through the whole file and fix the formatting as such (delete the colon, leave only one space between 'group' and the number, and ultimately then remove everything after the number):

group 43
group 312
group 501210

It should then be saved to that same file, list.txt, overwriting the previous contents. However, I can't even figure out how to remove the ':'..

Here's my code...

for line in $(< list.txt);do
sed 's/:/""/';
done

It appears to load the first line and then is lost in an infinite loop. Can anyone help?

Upvotes: 0

Views: 5704

Answers (2)

Scrutinizer
Scrutinizer

Reputation: 9936

Since this is about learning bash scripting you could do:

while read group nr rest
do
  printf "%s %d\n" "${group%:}" "$nr"
done < file > newfile && mv newfile file

or if "group" does not vary in the input file:

while read group nr rest
do
  printf "group %d\n" "$nr"
done < file > newfile && mv newfile file

But this would typically be slower than using sed, awk, etc..

Upvotes: 1

Kent
Kent

Reputation: 195179

you don't need the for loop. sed one liner could do the job:

sed -ir 's/(group):( [0-9]+).*/\1\2/' list.txt

or the awk one-liner:

awk -F': | ' '{print $1,$2}' list.txt > /tmp/t.tmp && mv /tmp/t.tmp /path/to/list.txt

Upvotes: 3

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