How to append multiple lines to a file

Question

I am writing a bash script to look for a file if it doesn't exist then create it and append this to it:

Host localhost
    ForwardAgent yes

So "line then new line 'tab' then text" I think its a sensitive format. I know you can do this:

cat temp.txt >> data.txt

But it seems weird since its two lines. Is there a way to append that in this format:

echo "hello" >> greetings.txt

Hauke Laging · Accepted Answer · 2022-09-30T08:24:48.067

1093

# possibility 1:
echo "line 1" >> greetings.txt
echo "line 2" >> greetings.txt

# possibility 2:
echo "line 1
line 2" >> greetings.txt

# possibility 3:
cat <<EOT >> greetings.txt
line 1
line 2
EOT

# possibility 4 (more about input than output):
arr=( 'line 1' 'line 2' );
printf '%s\n' "${arr[@]}" >> greetings.txt

If sudo (other user privileges) is needed to write to the file, use this:

# possibility 1:
echo "line 1" | sudo tee -a greetings.txt > /dev/null
possibility 3:
sudo tee -a greetings.txt > /dev/null <<EOT
line 1
line 2
EOT

edited Sep 30 '22 at 08:24

answered May 27 '13 at 14:54

Hauke Laging

90,279

12

@TheLegend That is called a "here document". Have a look at that paragraph in the man page. – Hauke Laging May 27 '13 at 15:00
4

One more possibility is ( echo "line 1" ; echo "line 2" ) >>greetings.txt. – ott-- May 27 '13 at 15:38
8

@ott-- You don't need a real subshell (i.e. can save one new process), this is enough: { echo "line 1" ; echo "line 2"; } >>greetings.txt – Hauke Laging May 27 '13 at 16:10
Indeed, {} is the better idea. – ott-- May 27 '13 at 18:02
Bash's built-in echo supports -e, so that's another possibility. Also, $'line1\nline2\nline3' is another bash feature. – derobert Sep 05 '14 at 20:43
3

whts the difference between EOT and EOL? – cikatomo Jan 09 '16 at 18:34
31

@cikatomo In cat <<EOT the EOT is just a random string. Could be cat <<FOO, too. – Hauke Laging Jan 09 '16 at 20:37
Question: won't option 3 be subject to tab completion and variable replacement making it unreliable? Also I've seem some people use cat <<EOT others cat <<"EOT" and some even cat <<'EOT'. Don't we need to quote it? What are the downsides of not quoting? – TCB13 Jan 26 '19 at 22:55
1

@TCB13 Whether the EOT is quoted (somehow) determines whether parameter expansion, command substitution, and arithmetic expansion are applied to the lines. – Hauke Laging Jan 30 '19 at 15:02
@HaukeLaging what if one doesn't one any kind of parameter expansion? Just the lines going into the file? – TCB13 Jan 30 '19 at 23:27
2

@TCB13 cat <<"EOT" ... EOT prevents expansion of parameters and shell variables. – tillmo Feb 02 '19 at 19:38
3

@cikatomo fyi, EOT, EOL, EOF acronyms stand for end of transmission/line/file respectively – whyer Nov 24 '19 at 14:22
1

How to write multi-line script without it being evaluated ? <<EOT evaluates some of my commands unfortunately. – Alexandre A. Apr 08 '20 at 11:54
@AlexandreA. From the man page, slightly modified: If any part of EOT is quoted, the delimiter is the result of quote removal on word, and the lines in the here-document are not expanded." So use e.g. <<"EOT" Now that I have written this I notice that this has been answered already, to comments before yours. – Hauke Laging Apr 15 '20 at 16:51

score 97 · Answer 2 · answered Jul 30 '14 at 16:21

97

echo -e "Hello \nWorld \n" >> greetings.txt

answered Jul 30 '14 at 16:21

kendotwill

1,079

score 82 · Answer 3 · edited Jun 11 '20 at 14:16

82

Another approach is to use tee

tee -a ~/.ssh/config << END
Host localhost
  ForwardAgent yes
END

A few choice lines from tee's man page:

The tee utility copies standard input to standard output, making a copy in zero or more files.

-a - Append the output to the files rather than overwriting them.

edited Jun 11 '20 at 14:16

Community

1

answered Aug 08 '17 at 11:09

+1 tee tends to work with paths that require sudo (solutions that use > >> < << often have trouble with paths that require sudo) – neoakris Sep 16 '22 at 15:21

score 75 · Answer 4 · edited Feb 24 '22 at 09:17

75

printf '%s\n    %s\n' 'Host localhost' 'ForwardAgent yes' >> file.txt

Or, if it's a literal tab that you want (rather than the four spaces in your question):

printf '%s\n\t%s\n' 'Host localhost' 'ForwardAgent yes' >> file.txt

You can achieve the same effect with echo, but exactly how varies from implementation to implementation, whereas printf is consistent.

edited Feb 24 '22 at 09:17

Stephen Kitt

434,908

answered May 27 '13 at 14:57

evilsoup

6,807
3
34
40

score 43 · Answer 5 · answered Apr 12 '18 at 07:44

43

Here is an example to append multiple lines in a file:

{
        echo '  directory "/var/cache/bind";'
        echo '  listen-on { 127.0.0.1; };'
        echo '  listen-on-v6 { none; };'
        echo '  version "";'
        echo '  auth-nxdomain no;'
        echo '  forward only;'  
        echo '  forwarders { 8.8.8.8; 8.8.4.4; };'
        echo '  dnssec-enable no;'
        echo '  dnssec-validation no;'
} >> your_file.txt

answered Apr 12 '18 at 07:44

user2753331

531

9

It is worth to note that this variant is part of the ShellCheck recommendation https://github.com/koalaman/shellcheck/wiki/SC2129 – mloskot Dec 11 '20 at 15:32

OB7DEV · Answer 6 · 2016-03-18T23:46:39.637

8

SED can append a line to the end of a file like so:

sed -i '$ a text to be inserted' fileName.file
$ selects end of file, the a tells it to append, and after this comes the text that is to be inserted. Then of course the file name.

Source: http://www.yourownlinux.com/2015/04/sed-command-in-linux-append-and-insert-lines-to-file.html

==========EDIT============

Does this approach have any added benefit than other solutions?
Yes, this approach has the added benefit of appending to any files return in a search, such as this: find . -name "*.html" -exec sed -i '$ a </html>' {} \;

I used the above example to insert the ending html tag that was missing on every html page within a number of directories.

===================================

edited Mar 18 '16 at 23:46

answered Mar 18 '16 at 19:40

OB7DEV

201

1

If you would show the syntax for appending multiple lines to a file, then this would be an answer to the question (although not a very useful one). All the other answers simply write the new text. This answer reads the entire file and rewrites it, plus the added text. Does this approach have any benefit over the others? – G-Man Says 'Reinstate Monica' Mar 18 '16 at 20:09
This only works with GNU sed. BSD sed bails with the error: command a expects \ followed by text. So don't use this for a scripted solution; it's liable to break. (Or do it properly as the BSD required syntax is POSIX compatible and will work on GNU sed as well. – Wildcard Mar 18 '16 at 20:28
1

The other answers can be used with find as follows: find . -name "*.txt" -exec sh -c 'printf "%s\n\t%s\n" "Host localhost" "ForwardAgent yes" >> "$1"' sh {} ";". – G-Man Says 'Reinstate Monica' Mar 19 '16 at 04:12
1

This is a very good solution, as it does not do stream redirection (>, >>) and thus does not suffer from their problems such as running sudo echo 'something' > /file. For me it perfectly allows to append a line to a file in lxd container like that: lxc exec c sed -- '$ a newline' /myfile. – Draco Ater Aug 23 '16 at 19:19
The echo "a new line" >> foo.file will not create a new line when the file is not end of new line, but sed -i '$ a a new line' foo.file will do, so sed is better especially you want always append a new line to the file. – zhouji Sep 12 '16 at 10:27

score 2 · Answer 7 · edited May 24 '16 at 18:55

2

I used sed because it can be used with sudo. For example:

sudo sed -i '$ a text to be inserted' fileName.file

the alternative is very ugly like :

sudo bash -c "echo a text to be inserted >> fileName.file"

and even uglier when done with ssh.

edited May 24 '16 at 18:55

sam

22,765

answered May 24 '16 at 18:34

Fred Mehrdad

31

score 2 · Answer 8 · answered Jun 27 '17 at 15:15

2

Another one liner is:

echo "Greetings 1" >> greetings.txt && echo "Greetings 2" >> greetings.txt

I'd prefer the -e option thought, as it gives more control:

echo -e "Greeting 1\nGreetings 2\n" >> greetings.txt

answered Jun 27 '17 at 15:15

Erdal G.

121

score 1 · Answer 9 · answered Dec 03 '17 at 02:55

One can emulate cat >> out.txt with either Perl or Python to achieve same effect. Perl:

perl -e 'open(fh,">>","./out.txt");while(<>){printf(fh "%s",$_)};close(fh);'

And Python:

python -c 'import sys;f=open(sys.argv[1],"a");l=[i for i in sys.stdin];f.write("".join(l))' out.txt

Note that for python you'll have to hit Ctrl+D twice. See related question on stackoverflow for more info.

score 0 · Answer 10 · answered Jun 07 '18 at 19:50

0

In addition to main answer, in case the file needs super user permissions, just adding sudo in front of echo won't work.

This is because shell breaks the commands and though echo did run as root, but >> ran with normal privileges.

This will work for super user: sudo su -c "echo 'Line 3' >> greetings.txt"

answered Jun 07 '18 at 19:50

SJ00

101

1

You don't need the su here (sudo su is not good). But you're right in that you need something do manage the shell redirection; perhaps sudo sh -c "echo stuff >> file.txt". No net saving but a better practice. – Chris Davies Aug 08 '19 at 13:51

Bog · Answer 11 · 2023-12-18T19:16:41.003

0

This should be illegal, but it I love it:

<<EOF>> your_file.txt cat
line 1
line 2
EOF

This combines here-docs with this funny shell behavior :)

edited Dec 18 '23 at 19:16

answered Oct 25 '23 at 14:58

Bog

989

How to append multiple lines to a file

11 Answers11

possibility 3:

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