Question

108

Is there any significance to using tee?

rated 0 times [ 108] [ 0] / answers: 1 / hits: 52184 / 1 Year ago, mon, may 15, 2023, 4:08:48

Why is it that almost all instructions regarding appending text to system files like fstab and /etc/apt/sources.list.d/<name>.list involve using tee and echo to append said text?

Take the following examples, which are run as root:

## 1

echo 'deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen' | tee -a file1

## 2

echo 'deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen' >> file2

Running diff -u file1 file2 returns nothing; running md5sum file1 file2 shows their checksums are identical, which brings me back to my original question:

Why is the | tee <FILENAME> so prevalent across Ubuntu docs, is it just good practice, otherwise wouldn't it be easier to just use example 2 instead of passing the output from echo to tee?

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termetalli

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answered 1 Year ago cklaceowne · Accepted Answer

There is a difference: tee duplicates the output: it sends it both to the file and to the display.

But there is more:

For example, if you want to write some string into two files at once, the command with tee you can use is:
```
 echo "some text" | tee file1 > file2  
```

Another thing tee can help you is to avoid one problem when using sudo. The normal output redirection operator is always executed with your user privileges, also when you write a sudo in front of the command which generates the STDOUT text. In other words, this will fail if you dont have the permission to write to that file:
```
 sudo echo "something" > bar  
```
But with tee, everything will go well:
```
echo "something" | sudo tee bar  
```

2 examples from this site. It has some more.