Software >> OS >> Unix >> Shell >> Commands >> tee >> How to use tee to read from standard input and write to both standard output and file


## e.g. pipe the output of your bash command or script to use tee to display both on screen and capture to a file


[root@mail tmp]# ls -ltr | tee myoutput.txt
total 0
drwx------. 3 root root 17 Sep 15 08:27 systemd-private-63530bc877e74e3a8a833e980562977c-chronyd.service-CbyYdV
drwxrwxrwt. 2 root root  6 Sep 15 08:27 cloud-init
drwx------. 3 root root 17 Sep 15 08:27 systemd-private-63530bc877e74e3a8a833e980562977c-dovecot.service-FbbBPz
drwx------. 3 root root 17 Sep 21 03:25 systemd-private-63530bc877e74e3a8a833e980562977c-mariadb.service-tH8Upy
drwx------. 3 root root 17 Sep 21 03:25 systemd-private-63530bc877e74e3a8a833e980562977c-httpd.service-mBQJmZ
-rw-r--r--. 1 root root  0 Sep 21 21:48 myoutput.txt


## display the file captured

[root@mail tmp]# cat myoutput.txt
total 0
drwx------. 3 root root 17 Sep 15 08:27 systemd-private-63530bc877e74e3a8a833e980562977c-chronyd.service-CbyYdV
drwxrwxrwt. 2 root root  6 Sep 15 08:27 cloud-init
drwx------. 3 root root 17 Sep 15 08:27 systemd-private-63530bc877e74e3a8a833e980562977c-dovecot.service-FbbBPz
drwx------. 3 root root 17 Sep 21 03:25 systemd-private-63530bc877e74e3a8a833e980562977c-mariadb.service-tH8Upy
drwx------. 3 root root 17 Sep 21 03:25 systemd-private-63530bc877e74e3a8a833e980562977c-httpd.service-mBQJmZ
-rw-r--r--. 1 root root  0 Sep 21 21:48 myoutput.txt


## If you want to append to existing file, use -a option

[root@mail tmp]# echo "LINE BEFORE" > myoutput.txt

[root@mail tmp]# cat myoutput.txt
LINE BEFORE

[root@mail tmp]# ls -ltr | tee -a myoutput.txt
total 4
drwx------. 3 root root 17 Sep 15 08:27 systemd-private-63530bc877e74e3a8a833e980562977c-chronyd.service-CbyYdV
drwxrwxrwt. 2 root root  6 Sep 15 08:27 cloud-init
drwx------. 3 root root 17 Sep 15 08:27 systemd-private-63530bc877e74e3a8a833e980562977c-dovecot.service-FbbBPz
drwx------. 3 root root 17 Sep 21 03:25 systemd-private-63530bc877e74e3a8a833e980562977c-mariadb.service-tH8Upy
drwx------. 3 root root 17 Sep 21 03:25 systemd-private-63530bc877e74e3a8a833e980562977c-httpd.service-mBQJmZ
-rw-r--r--. 1 root root 12 Sep 21 21:50 myoutput.txt

[root@mail tmp]# cat myoutput.txt
LINE BEFORE
total 4
drwx------. 3 root root 17 Sep 15 08:27 systemd-private-63530bc877e74e3a8a833e980562977c-chronyd.service-CbyYdV
drwxrwxrwt. 2 root root  6 Sep 15 08:27 cloud-init
drwx------. 3 root root 17 Sep 15 08:27 systemd-private-63530bc877e74e3a8a833e980562977c-dovecot.service-FbbBPz
drwx------. 3 root root 17 Sep 21 03:25 systemd-private-63530bc877e74e3a8a833e980562977c-mariadb.service-tH8Upy
drwx------. 3 root root 17 Sep 21 03:25 systemd-private-63530bc877e74e3a8a833e980562977c-httpd.service-mBQJmZ
-rw-r--r--. 1 root root 12 Sep 21 21:50 myoutput.txt