cmd="" cmd=$cmd"cat 1.txt | " cmd=$cmd"sort | " cmd=$cmd"uniq > 2.txt" eval $cmd

cat aaa.txt | while read line do echo $line done

echo 12345 | cut -c-3

file_s="./*" for file_1 in $file_s; do echo $file_1 done

echo "aaa.txt" | sed -e "s/\.txt//g"

echo -n 999