tee

Dit deel is nog niet vertaald. Je ziet de Engelse tekst.

Wat het doet

tee sits in a pipe like a T-piece in a water pipe: data goes through, and a copy goes into files. You see the output and keep it.

A very common use: write to a file that only root may change, from a normal user, with echo ... | sudo tee FILE. The redirect > would run as your user and fail; tee runs with sudo.

Zo schrijf je het

tee [OPTION]... [FILE]...

Opties 6

Meest gebruikt

-a, --append: Add to the end of the files instead of overwriting them.
-i, --ignore-interrupts: Ignore Ctrl+C (the interrupt signal).
-p: Report errors when writing to pipes (and go on with other outputs).
--output-error[=MODE]: What to do when a write fails: warn, warn-nopipe, exit, exit-nopipe.
--help: Show help.
--version: Show the version.

Voorbeelden 11

$ als gewone gebruiker# als root (of met sudo)

1See the output and save it
```
$dnf check-update | tee updates.txt
```
You watch the list and keep a copy for your change ticket.
2Write a root-owned file from a normal user
```
$echo "net.ipv4.ip_forward = 1" | sudo tee /etc/sysctl.d/90-forward.conf
```
sudo echo ... > file fails because the redirect is not done by sudo.
3Add a line to a root-owned file
```
$echo "192.168.122.20 server2" | sudo tee -a /etc/hosts
```
-a appends. Without it the file would be replaced.

4Hide tee's copy on the screen

$echo "export EDITOR=vim" | sudo tee /etc/profile.d/editor.sh > /dev/null

Only the file gets the text.

5Write several files at once

$ip -br a | tee /tmp/net-$(hostname).txt /srv/reports/net-latest.txt

One command, two copies.

6Log a long script and still watch it
```
$./upgrade.sh 2>&1 | tee -a /var/tmp/upgrade-$(date +%F).log
```
2>&1 sends errors into the pipe too, so the log is complete.
7Save the middle of a pipe
```
$journalctl -u sshd --since today | tee ssh-today.log | grep -c "Failed password"
```
The full log is saved; the screen shows only the count of failed logins.

8Write a heredoc to a protected file

$sudo tee /etc/yum.repos.d/local.repo > /dev/null <<'EOF'
[local-baseos]
name=Local BaseOS
baseurl=file:///repo/BaseOS
gpgcheck=0
EOF

A clean way to create config files in scripts that run as a normal user with sudo.

9Keep running when you press Ctrl+C
```
$ping server2 | tee -i ping.log
```
With -i, tee is not stopped by Ctrl+C, so the log gets the last lines.
10Record a kubectl apply for the change log
```
$kubectl apply -f deploy.yaml 2>&1 | tee -a changes.log
```
Every change is visible now and stored for later.
11Count and save matches at the same time
```
$grep "ERROR" app.log | tee errors.txt | wc -l
```
The number on the screen, the lines in the file.

Let op

Without -a, tee overwrites the file.
In sudo tee, only tee runs as root; the command before the pipe runs as you.

Tips om te onthouden

tee = T-piece: one input, two outputs (screen + file).
| sudo tee FILE = write as root. | sudo tee -a FILE = append as root.

`tee`

Wat het doet

Zo schrijf je het

Opties 6

Voorbeelden 11

1See the output and save it

2Write a root-owned file from a normal user

3Add a line to a root-owned file

4Hide tee's copy on the screen

5Write several files at once

6Log a long script and still watch it

7Save the middle of a pipe

8Write a heredoc to a protected file

9Keep running when you press Ctrl+C

10Record a kubectl apply for the change log

11Count and save matches at the same time

Let op

Tips om te onthouden

Volledige handleiding

Wat het doet

Zo schrijf je het

Opties 6

Voorbeelden 11

1See the output and save it

2Write a root-owned file from a normal user

3Add a line to a root-owned file

4Hide tee's copy on the screen

5Write several files at once

6Log a long script and still watch it

7Save the middle of a pipe

8Write a heredoc to a protected file

9Keep running when you press Ctrl+C

10Record a kubectl apply for the change log

11Count and save matches at the same time

Let op

Tips om te onthouden

Verwante commando's

Gebruikt in deze lessen

Gebruikt in deze labs

Volledige handleiding

`tee`