how to read line by line from file in bash script?

Question

I've searched online about this problem and I've found two ways so far:

   while read line; do
      commands
   done < "$filename"

and

    for $line in $(cat $filename); do
       commands
    done

none of these work if the lines have a space though, for example if we have a line like that

  textextext text

it won't print textextext text

but

  textextext
  text

it counts these things as a different line, how can I avoid this to happen?

Are you interested a) in leading and trailing whitespace or b) in intermediate whitespace (e.g. multiple spaces) or c) only in the words in one line? — A.H., Oct 31 '11 at 18:01

Michael Krelin - hacker · Accepted Answer · 2011-10-31T17:49:49.327

9

Like this?

while IFS= read line ; do
   something "$line"
done <"$file"

Here is a brief test:

while IFS= read line ; do echo "$line"; done <<<"$(echo -e "a b\nc d")"
a b
c d

edited Oct 31 '11 at 17:49

answered Oct 31 '11 at 17:36

isn't this the same thing I posted? I think this won't work if the line has a space – jonathan Oct 31 '11 at 17:42
empties input field separator. I've just updated post with the test I've just conducted. – Michael Krelin - hacker Oct 31 '11 at 17:50
thanks it worked great right now, I made a mistake on my first test – jonathan Oct 31 '11 at 17:58
3

the other key diff is the addition of dbl-quotes around your ${line} variable. Good luck. – shellter Oct 31 '11 at 18:07
You're welcome. Double quotes wouldn't make it break lines, tho :) – Michael Krelin - hacker Oct 31 '11 at 19:40
1

You might want to add the -r option to read as per https://stackoverflow.com/a/10929955/770191 – Albino Cordeiro Feb 26 '18 at 19:33
@AlbinoCordeiro, that's right, though, depends on how you want to handle escaped stuff. – Michael Krelin - hacker Mar 04 '18 at 18:13

score 7 · Answer 2 · answered Oct 31 '11 at 17:54

7

You can you readarray (bash 4+)

readarray lines < "$file"

then

for line in "${lines[@]}"; 
do
    echo "$line"
done

Note that by default readarray will even include the line-end character for each line

answered Oct 31 '11 at 17:54

sehe

1

The "-t" arg to readarray will "remove a trailing newline from each line read." – Tripp Lilley Feb 11 '12 at 11:00

2 Answers2