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I want to do:

echo "something" >> /etc/config_file

But, since only the root user has write permission to this file, I can't do that. But the following also doesn't work.

sudo echo "something" >> /etc/config_file

Is there a way to append to a file in that situation without having to first open it with a sudo'd editor and then appending the new content by hand?

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9 Answers 9

Reset to default
468

Use tee -a (or tee --append) with sudo

tee - read from standard input and write to standard output and files
[...]
   -a, --append
      append to the given FILEs, do not overwrite
[...]

So your command becomes

echo "something" | sudo tee -a /etc/config_file

The advantages of tee over executing Bash with administrative permissions are

  • You do not execute Bash with administrative permissions
  • Only the 'write to file' part runs with advanced permissions
  • Quoting of a complex command is much easier
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  • 2
    On OS X tee only seems to have an -a flag.
    – Lri
    Jun 20, 2012 at 14:48
  • Debian 8 tee has the -a append flag.
    – clay
    Mar 13, 2017 at 18:46
  • 20
    Use echo "output" | sudo tee -a file > /dev/null if you want to skip console output.
    – Moshe Bixenshpaner
    Sep 22, 2017 at 1:16
  • Works well for WSL as well.
    – kayleeFrye_onDeck
    Dec 8, 2017 at 0:18
  • What if "something" is some secret value, that you don't want to be outputted to the terminal and potential be saved in logs etc.?
    – quapka
    Aug 11, 2020 at 14:45
59

The redirection is executed in the current shell. In order to do the redirection with elevated privileges, you must run the shell itself with elevated privileges:

sudo bash -c "somecommand >> somefile"
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26

Have sudo spawn a sub-shell:

sudo sh -c "echo 'JAVA_HOME=/usr/lib/jvm/java-6-sun' >> /etc/profile"

In this example, sudo runs "sh" with the rest as arguments.

(this is shown as an example in the sudo man page)

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  • 8
    The reason is that it's your shell (running as you) that does the redirection, not sudo. Since you don't have permission to write to the file, you get the Permission denied error. What this answer does is to start a new shell that is running as root, and therefore is able to write to the file.
    – Randy Orrison
    Oct 13, 2009 at 14:48
  • This is not the right answer. This is a right answer. Akira's got a better one, for the logic provided in that answer.
    – TOOGAM
    Jun 16, 2016 at 17:42
14

I usually use shell HERE document with sudo tee -a. Something along the lines of:

sudo tee -a /etc/profile.d/java.sh << 'EOF'
# configures JAVA
JAVA_HOME=/usr/lib/jvm/java-8-oracle
export JAVA_HOME
export PATH=$PATH:$JAVA_HOME/bin
EOF
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6

In my opinion, the best in this case is dd:

sudo dd of=/etc/profile <<< END
JAVA_HOME=/usr/lib/jvm/java-6-sun
END
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  • 1
    Be careful. This command would overwrite /etc/profile. You should add "conv=notrunc oflag=append" arguments to achieve the desired behavior.
    – likebike
    Oct 3, 2021 at 11:51
5

This is very simple and puts sudo first, as it is common.

sudo sed -i '$a something' /etc/config_file

$a means to append at the end of the file.

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There may be a problem with the sudo here and the redirecting. Use a texteditor of your choice instead to add the line.

sudo nano /etc/profile

Or, you could try su instead

su
echo ‘JAVA_HOME=/usr/lib/jvm/java-6-sun’ >> /etc/profile
exit
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  • Unfortunately, this produced the same result.
    – Matt Norris
    Oct 13, 2009 at 14:57
  • 1
    su -c 'echo "JAVA_HOME=/usr/lib/jvm/java-6-sun" >> /etc/profile' should work. since there's nothing the shell can mistakenly expand in the arg to echo, single-quote the overall command.
    – quack quixote
    Oct 13, 2009 at 15:55
  • That's fantastic. Now do this as part of a script.
    – Ernie Dunbar
    May 9, 2018 at 16:02
0

This won't work you are trying to redirect (using >>) the output of sudo. What you really want to do is redirect the output of echo. I suggest you simply use your favorite editor and add that line manually to /etc/profile. This has the additional benefit that you can check whether /etc/profile already sets JAVA_HOME.

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Use ex-way:

sudo ex +'$put =\"FOO\"' -cwq /etc/profile

and replace FOO with your variable to append.

In some systems (such as OS X), the /etc/profile file has 444 permissions, so if you still getting permission denied, check and correct the permission first:

sudo chmod 644 /etc/profile

then try again.

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