Use sudo tee with heredoc to append to existing file

Question

sudo tee "$OUTFILE" > /dev/null <<'EOF'
foo
bar
EOF

However, I would like to use that approach to append to an existing file $OUTFILE. The above method overwrites existing file $OUTFILE.

@couling-comments like this fail to consider a couple things. First, when I asked the question I was grappling with heredocs, redirection, sudo & tee. For all I knew, the issue could have been related to my usage of heredocs or something else. Second, I was not even sure the tee approach was the right one. Granted, I could have read all the manuals for every element of my proposed solution and all my alternatives. But if everyone did that, we wouldn't need a place like this to ask questions. Finally, I don't think your comment respects Stack Exchange etiquette (although I am not entirely sure) — MountainX
– MountainX, Commented Jul 21, 2013 at 18:48
firstly this was intended as a polite pointer to which manual was appropriate not a blind "RTFM". That's well within stack exchange etiquette. Secondly it is also good etiquette to explain how to find an answer as well as simply give one. To that end: if a file is being overwritten and that file is only referenced as an argument to a command, I'd start with the manual for that command not read every possible manual for your code. man sudo would fairly quickly point you to the fact that tee is a command in it's own right, thus lead you to man tee. — Philip Couling
– Philip Couling, Commented Jul 22, 2013 at 11:44

jordanm · Accepted Answer · 2013-07-21 04:16:47Z

20

You want the -a option to tee which appends rather than overwriting.

answered Jul 21, 2013 at 4:16

jordanm

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Cbhihe · Accepted Answer · 2020-03-10 15:31:28Z

5

If you prefer to use cat, then go this route, first passing $OUTFILE as your output's receptacle:

$ OUTFILE=/path/to/restricted_write_access/file
$ sudo out=$OUTFILE sh -c 'cat << EOF >> $out
foo
bar
EOF'

answered Mar 10, 2020 at 11:37

Cbhihe

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trevorgrayson · Accepted Answer · 2015-06-30 16:41:02Z

1

tee requires you to open up a stream to /dev/null, you can get away doing this with a simple cat

cat <<EOF >> $OUTFILE
foo
bar
EOF

Save your keyboard!

answered Jun 30, 2015 at 16:41

trevorgrayson

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3 Answers 3