$ echo hengwei-2018 > a.txt $ echo hengwei_2019 >> a.txt # ==========1============= $ for line in `cat a.txt`; do echo $line; done hengwei-2018 hengwei_2019 # ==========2============= $ while read line; do echo $line; done < a.txt hengwei-2018 hengwei_2019 # ==========3============= $ cat a.txt | while read line; do echo $line; done hengwei-2018 hengwei_2019 # ==========4============= $ for line in $(<a.txt); do echo $line; done hengwei-2018 hengwei_2019 # ==========5============= $ for i in `<a.txt`; do echo $i; done hengwei-2018 hengwei_2019