AWK - Delete both leading and trailing whitespaces from each line

awk '{ gsub(/^[ \t]+|[ \t]+$/, ""); print }' file.txt

Example

file.txt
aaaaa
    bbbbb
        ccccc
 ddddd
 
       eeeee

returns: 

aaaaa
bbbbb
ccccc
ddddd
 
eeeee