I have a text.txt file like this
line1
line2
line3
I want to write a script that loops over each line and echo out
modified line1
modified line2
modified line3
This is the script which is a very common solution:
while IFS= read -r line; do
echo modified $line
done <<< $(cat ~/text.txt)
But the output I got was:
modified line1 line2 line3
What went wrong?
The issue is in the last line, you don't need the variable (command substitution) or cat, since read already can read the file. If you instead do this:
while IFS= read -r line; do
echo modified $line
done < ~/text.txt
It works.
Additionally, your command would work if you quoted the variable like:
"$(cat ~/text.txt)"
since bash disregards newlines in variables unless you quote them. But doing it this way is overcomplicating it.
cat command or the variable (the result of the cat command) in the last line.
command substitution and heredoc is not necessary here, but I don't understand why that combination doesn't work. Would you mind explaining that?
"$(cat /tmp/text.txt)" it would work, but this is overcomplicating it.
<<< $(cat ...)command substitution + here string is completely unnecessary and messing things up, but I guess that you're using some older (< 4.0?) version ofbash, which will ifs-split+glob the word following<<<.ifs-split+glob the word following <<<?IFSvariable and then glob-expand the resulting words (eg.a='* .*'; echo $a). This should not happen on a variable used as a here-string (eg.a='* .*'; cat <<<$ashould print just* .*), but it does happen on some older buggy versions ofbash.