Appending files in linux

Linux append text to end of file

You need to use the >> to append text to end of file. It is also useful to redirect and append/add line to end of file on Linux or Unix-like system.

How to redirect the output of the command or data to end of file

The procedure is as follows

1. Append text to end of file using echo command:
   echo ‘text here’ >> filename
2. Append command output to end of file:
   command-name >> filename

How to add lines to end of file in Linux

The >> is called as appending redirected output. Create the file if does not exists. For example, append some networking command to net.eth0.config.sh script:
echo ‘I=eth0’ >> net.eth0.config.sh
echo ‘ip link set $I up’ >> net.eth0.config.sh
echo ‘ip addr add 10.98.222.5/255.255.255.0 dev $I’ >> net.eth0.config.sh
echo ‘ip route add default via 10.98.222.1’ >> net.eth0.config.sh

You can also add data to other config files. Another option is to run command and append output to a file. Run data command at the terminal and append output to output.txt:
date >> output.txt
Execute ls command and append data to files.txt:
ls >> files.txt
To see files.txt use cat command:
cat files.txt
more files.txt
less files.txt

How to append standard output and standard error

The following sytax allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be appended to the file name. The format for appending standard output and standard error is:
echo ‘text’ &>>filename
command &>>filename
find . type d -name «*.projects» &>> list.txt
This is semantically equivalent to
echo ‘text’ >>fileNameHere 2>&1
command >>fileNameHere 2>&1
date >>data.txt 2>&1

For more info read redirection topic.

Append text when using sudo

Try the tee command:
echo ‘text’ | sudo tee -a my_file.txt
echo ‘104.20.186.5 www.cyberciti.biz’ | sudo tee -a /etc/hosts
Of coruse we can use following syntax to append text to end of file in Linux
sudo sh -c ‘echo my_text >> file1’
sudo — bash -c ‘echo «some data» >> /my/path/to/filename.txt’
The -c option passed to the bash/sh to run command using sudo.
See “how to append text to a file when using sudo command on Linux or Unix” for more info.

Conclusion – Append text to end of file on Unix

To append a new line to a text on Unix or Linux, try:

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How To Use Cat Command To Append Data To a File on Linux/Unix

I am a new Unix user. I have Debian Linux installed. I need to append text to a file called daily.log. How do I use the cat command to append data to a file?

You can use the cat command to append data or text to a file. The cat command can also append binary data. The main purpose of the cat command is to display data on screen (stdout) or concatenate files under Linux or Unix like operating systems. To append a single line you can use the echo command or printf command command. Let us see how to use the cat command to append data and update files without losing its content.

Tutorial details
Difficulty level	Easy
Root privileges	No
Requirements	cat on Linux or Unix
Est. reading time	2 mintues

How To Use Cat Command To Append Data To a File on Linux/Unix

Redirection symbol is as follows for appending data to a file:

Syntax

Examples

Create a text file called foo.txt, type:

To save the changes press CTRL-d i.e. press and hold CTRL and press d. Create another text file called bar.txt as follows:

Display both files on the screen, enter:

To append a contains of bar.txt to to foo.txt, enter:

To append a ‘Use unix or die’ text to foo.txt file, enter:

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Fig.01: Using the cat and echo command to append a text to a file.

Append text to a file when using sudo command

We can use the echo command or printf command to append data to a file called sales.txt in the current directory:

Want to append to a file? Try:
cat filename | sudo tee -a foo_file.txt
In this example append data using the following syntax:
sudo sh -c ‘echo «192.168.1.253 wireless-router» >> /etc/hosts’
Verify it:
cat /etc/hosts

Summing up

We explained various Linux and Unix commands that one could use to append data to a file. Although I tested all examples on Bash running on macOS and Linux desktop, these examples should work with other shells, too, such as:

🐧 Get the latest tutorials on Linux, Open Source & DevOps via

Category	List of Unix and Linux commands
Documentation	help • mandb • man • pinfo
Disk space analyzers	df • duf • ncdu • pydf
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Package Manager	apk • apt
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Searching	ag • grep • whereis • which
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Comments on this entry are closed.

when i execute two commands like echo $val(nn) > t.txt and awk -f throughput.awk wpan.tr >t.txt
i want the file t.txt to have two columns side by side leaving a tab or space in between. but i m getting output like this

pls help in this regard…thanks

I’m not sure I understood your query. To merge corresponding or subsequent lines of files try paste command.

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How to append one file to another in Linux from the shell?

I have two files: file1 and file2 . How do I append the contents of file2 to file1 so that contents of file1 persist the process?

8 Answers 8

cat file2 >> file1

The >> operator appends the output to the named file or creates the named file if it does not exist.

cat file1 file2 > file3

This concatenates two or more files to one. You can have as many source files as you need. For example,

cat *.txt >> newfile.txt

Update 20130902
In the comments eumiro suggests «don’t try cat file1 file2 > file1 .» The reason this might not result in the expected outcome is that the file receiving the redirect is prepared before the command to the left of the > is executed. In this case, first file1 is truncated to zero length and opened for output, then the cat command attempts to concatenate the now zero-length file plus the contents of file2 into file1 . The result is that the original contents of file1 are lost and in its place is a copy of file2 which probably isn’t what was expected.

Update 20160919
In the comments tpartee suggests linking to backing information/sources. For an authoritative reference, I direct the kind reader to the sh man page at linuxcommand.org which states:

Before a command is executed, its input and output may be redirected using a special notation interpreted by the shell.

While that does tell the reader what they need to know it is easy to miss if you aren’t looking for it and parsing the statement word by word. The most important word here being ‘before’. The redirection is completed (or fails) before the command is executed.

In the example case of cat file1 file2 > file1 the shell performs the redirection first so that the I/O handles are in place in the environment in which the command will be executed before it is executed.

A friendlier version in which the redirection precedence is covered at length can be found at Ian Allen’s web site in the form of Linux courseware. His I/O Redirection Notes page has much to say on the topic, including the observation that redirection works even without a command. Passing this to the shell:

. creates an empty file named out. The shell first sets up the I/O redirection, then looks for a command, finds none, and completes the operation.

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How to append contents of multiple files into one file

I want to copy the contents of five files to one file as is. I tried doing it using cp for each file. But that overwrites the contents copied from the previous file. I also tried

and it did not work.

I want my script to add the newline at the end of each text file.

eg. Files 1.txt, 2.txt, 3.txt. Put contents of 1,2,3 in 0.txt

11 Answers 11

You need the cat (short for concatenate) command, with shell redirection ( > ) into your output file

Another option, for those of you who still stumble upon this post like I did, is to use find -exec :

In my case, I needed a more robust option that would look through multiple subdirectories so I chose to use find . Breaking it down:

Look within the current working directory.

Only interested in files, not directories, etc.

Whittle down the result set by name

Execute the cat command for each result. «+» means only 1 instance of cat is spawned (thx @gniourf_gniourf)

As explained in other answers, append the cat-ed contents to the end of an output file.

if you have a certain output type then do something like this

If all your files are in single directory you can simply do

Files 1.txt,2.txt, .. will go into 0.txt

If all your files are named similarly you could simply do:

I found this page because I needed to join 952 files together into one. I found this to work much better if you have many files. This will do a loop for however many numbers you need and cat each one using >> to append onto the end of 0.txt.

as brought up in the comments:

Another option is sed :

Or without redirection .

Note that last line write also merge.txt (not wmerge.txt !). You can use w»merge.txt» to avoid confusion with the file name, and -n for silent output.

Of course, you can also shorten the file list with wildcards. For instance, in case of numbered files as in the above examples, you can specify the range with braces in this way:

if your files contain headers and you want remove them in the output file, you can use:

If the original file contains non-printable characters, they will be lost when using the cat command. Using ‘cat -v’, the non-printables will be converted to visible character strings, but the output file would still not contain the actual non-printables characters in the original file. With a small number of files, an alternative might be to open the first file in an editor (e.g. vim) that handles non-printing characters. Then maneuver to the bottom of the file and enter «:r second_file_name». That will pull in the second file, including non-printing characters. The same could be done for additional files. When all files have been read in, enter «:w». The end result is that the first file will now contain what it did originally, plus the content of the files that were read in.

All of the (text-) files into one

xargs makes the output-lines of find . the arguments of cat.

find has many options, like -name ‘*.txt’ or -type.

you should check them out if you want to use it in your pipeline

If you want to append contents of 3 files into one file, then the following command will be a good choice:

It will combine the contents of all files into file4, throwing console output to /dev/null .

Not the answer you’re looking for? Browse other questions tagged linux bash unix or ask your own question.

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