Linux append to all files

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:

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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 can I append and prepend some text to all files in a folder in Linux

I have the folder structure like below

resources/folder1 , /folder2 , /folder3

Now I want this text to be prepended with newlines:

and this should appended at the bottom

of all the files in folder and sub-directories under Resources. Is this possible?

4 Answers 4

You can make that with sed :

Change directory to resources , create two template files: BEGIN and END .

File: BEGIN

File: END

Run commands:

No backslashs escaping any more, this solution is very clear and simple and scales well.

There are probably a myriad ways to do it. Subject to the file names not containing spaces or the like, then you can use:

The set of braces performs I/O redirection on the enclosed commands. They’re a little tricky to use accurately on the same line as commands, but the code above is easy. The redirection to tmp.$$ is OK if you are not working in a hostile environment; you might need to use mktemp or some other command if you think people might be subverting you while you run the script. The cp and rm done as shown means that you don’t run into problems if any of the files is actually a symlink (or a hard link); the links are preserved. Alternatives such as mv tmp.$$ $file would break links or symlinks.

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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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Append to list of files in bash

so I’m trying to get a simple bash script to continuously read a directory and update a list of files to play through a command. However, I’m having some trouble thinking out the logic in it. What I need to do is put the current items in the directory into the list, have each item in the directory run through a program, and when a new item comes in, just append it to the list. I’m attempting to use inotifywait but can’t seem to think of the proper logic. I may need it to run in the background, as the process that is running on these files will run before inotifywait is read again, at which point it will not pick up any new files that have been added as it only checks when it runs. Here’s the code so hopefully it makes more sense.

So for example. if rpitx is currently playing something, and a file is converted, it won’t pick up the latest file and add it to the list, nor will it make it since it’s always reading. Is there a way to get inotifywait to run in the background of this script somehow? Thanks.

1 Answer 1

This is actually quite a difficult problem to get 100% perfect, but it is possible to get pretty close.

It is easy to get all the files in a directory, and it is easy to use inotifywait to get iteratively informed of new files being placed into the directory. The issue is getting the two to be consistent. If inotifywait isn’t started until all the files have been processed (or even just listed), then you might miss new files created between the listing and the invocation of inotifywait . If, on the other hand, you start inotifywait first, then a file created after the invocation of inotifywait and the extraction of the current file list will be listed twice.

Since it is easier to filter duplicates than notice orphans, the recommended approach is the second one.

As a first approximation, we could ignore the duplicate problem on the assumption that the window of vulnerability is pretty short and so it is probably unlikely to happen. This simplifies the code, but it’s not that difficult to track and eliminate duplicates: we could, for example, store each filename as the key in an associative array, ignoring the file if the key already exists.

We need three processes: one to execute inotifywait ; one to produce the list of initial files; and one to handle each file as it is identified. So the basic structure of the code will be:

Note that the second process first produces the existing files, and then calls pass_through , which reads from standard input and writes to standard output, thus passing through the files being discovered by list_new_files . Since pipes have a finite capacity, it is possible that the execution of list_existing_files will block a few times (if there are lots of existing files and handling them takes a long time), so when pass_through finally gets executed, it could have quite a bit of queued-up input to pass through. That doesn’t matter, unless the first pipe also fills up, which will happen if a large number of new files are created. And that still won’t matter as long as inotifywait doesn’t lose notifications while it is blocked on a write. (This may actually be a problem, since the manpage for inotifywait on my system includes in the «BUGS» section the note, «It is assumed the inotify event queue will never overflow.» We could fix the problem by inserting another process which carefully buffers inotifywait ‘s output, but that shouldn’t be necessary unless you intend to flood the directory with lots of files.)

Now, let’s examine each of the functions in turn.

list_new_files could be just the call to inotifywait from your original script: inotifywait -m /home/pi/rpitx/converted -e create -e moved_to

Listing existing files is also easy. Here’s one simple solution:

However, that will print out the full file path, which is different from the output from inotifywait . To make them the same, we cd into the directory in order to do the listing. Since we might not actually want to change the working directory, we use a subshell by surrounding the commands inside parentheses:

The printf just prints its arguments each on a separate line. Since glob-expansions are not word-split or recursively glob-expanded, this is safe against whitespace or metacharacters in filenames, except newline characters. Filenames with newline characters are pretty rare; for now, I’ll ignore the issue but I’ll indicate how to handle it at the end.

Even with the change indicated above, the output from these two commands is not compatible: the first one outputs three things on each line (directory, action, filename), and the second one just one thing (the filename). In the listing below, you’ll see how we modify the format to printf and introduce a format for inotifywait in order to make the outputs fully compatible, with the «action» for existing files set to EXISTING .

pass_through could, in theory, just be cat , and that’s how I’ve coded it below. However, it is important that it operate in line-buffered mode; otherwise, nothing will happen until «enough» files have been written by list_existing_files . On my system, cat in this configuration works perfectly; if that doesn’t work for you or you don’t want to count on it, you could write it explicitly as a while read loop:

Finally, handle is essentially the code from the original post, but modified a bit to take the new format into account, and to do the right thing with action EXISTING .

What if we thought a filename might have a newline character in it? There are two «safe» characters which could be used to delimit the filenames, in the sense that they cannot appear inside a filename. One is / , which can obviously appear in a path, but cannot appear in a simple filename, which is what we’re working with here. The other one is the NUL character, which cannot appear inside a filename at all, but can sometimes be a bit annoying to deal with.

Normally, faced with this problem, we would use a NUL , but that depends on the various utilities we’re using allowing the separation of data with NUL instead of newline. That’s not the case for inotifywait , which always outputs a newline after a notification line. So in this case it seems simpler to use a / . First we modify the formats:

Now, when we’re reading the lines, we need to read until we find a line ending with / (and remember to remove it). read doesn’t allow two-character line terminators, so we need to accumulate the lines ourselves:

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