How can I read from multiple variables with a while read line? I'm trying to create a csv file from these variables which are multi-lined.
Not sure if this the best way to do this.
For example:
1st_list=$(..code..)
2nd_list=$(..code..)
while read line_from_1, line_from_2
do
echo "$line_from_1,$line_from_2" >> outputfile.csv
done < $1st_list,$2nd_list
Your question is a little unclear, but in order to read from multiple sources in parallel, you need to use multiple file descriptors and, I think, process substitution.
while read line_from_1;
read -u 3 line_from_2; do
echo "From first: $line_from_1"
echo "From second: $line_from_2"
done < <( echo "$first_list" ) 3< <(echo "$second_list")
(Of course, you don't have to use the two variables if they aren't preexisting; just put the code that populates each variable in the appropriate process substitution that feeds the while loop:
done < <( ...code for first list...) 3< <(...code for second list...)
)
As written, the loop will succeed as long as the second read succeeds (the exit status of the first read is ignored). To loop as long as both succeed, use read line_from_1 && read -u 3 line_from_2.
To loop as long as either succeeds, you'll need a slightly more complicated mini script as the while condition:
while read line_from_1; read1=$?;
read line_from_2; read2=$?;
(( read1 == 0 || read2 == 0 )); do
UPDATE: you can also simply use here strings if the variables are already set in place of the process substitutions. (I wasn't sure if 3<<< was legal.)
while read line_from_1; read -u 3 line_from_2; do
...
done <<< "$first_line" 3<<< "$second_line"
$first_list is emptied.
echo "$first_list" and echo "$second_list" with the code that actually generates them; that way the content doesn't need to be stored in memory.read line_from_2 <&3. We've already ditched POSIX compliance by using process substitutions, so I'll leave the fix for that (using here-documents containing command substitutions or using explicit named pipes) as an exercise for the reader.Assuming you want as output
file1line1,file2line1
file2line2,file2line2
etc.
then you don't need anything like this at all as paste does exactly that.
paste -d, <(echo "$first_list") <(echo "$second_list")
$1st_listand$2nd_list?line1,line2? `line1field1,line2field1,l1f2,l2f2,....'?>>outputfile.csvfrom theechoto a>outputfile.csvafter thedone-- that way you open the output file only once, rather than re-opening it (and then closing it) every single time you want to write a line.