How to expand bash variable in a string and preserve newline

问题

This one works for single line string:

var2="2018"
str="${var1:-hello} world! 
Happy $var2 new year $var2"

newstr=()
for cnt in "$str" ;do
    echo "$cnt"
    [ "${cnt:0:1}" == '$' ] && cnt=${cnt:1} && cnt=${!cnt}
    newstr+=($cnt)
done
newstr="${newstr[*]}"

How to preserve the newline?

回答1:

Even if I fail to fully understand what your goal is,
correctly quoting will preserve the new lines.

Change this two lines:

[ "${cnt:0:1}" == '$' ] && cnt="${cnt:1}" && cnt="${!cnt}"
newstr+=("$cnt")

回答2:

The purpose of the script is obscure to me, but here is the way I would write it to read line by line:

var2="2018"
str="${var1:-hello} world! 
Happy $var2 new year $var2"

newstr=()
while read cnt; do
    echo "$cnt"
    [ "${cnt:0:1}" == '$' ] && cnt=${cnt:1} && cnt=${!cnt}
    newstr+=($cnt)
done < <(echo "$str")
newstr="${newstr[*]}"

The read command reads one line after the other. The natural way to write it would be with a pipe:

var2="2018"
str="${var1:-hello} world! 
Happy $var2 new year $var2"

newstr=()
echo "$str" | while read cnt; do
    echo "$cnt"
    [ "${cnt:0:1}" == '$' ] && cnt=${cnt:1} && cnt=${!cnt}
    newstr+=($cnt)
done
newstr="${newstr[*]}"

However the pipe creates a subshell and the variables modified inside the while loop would be discarded once stepping out of it, here especially the newstr variable.

来源：https://stackoverflow.com/questions/39739673/how-to-expand-bash-variable-in-a-string-and-preserve-newline