Append lines to file linux

Append Lines to a File in Linux

Introduction In Linux, files are often used to store data that is either created by a program or generated by user. It is common for users to append new lines of data to existing files rather than creating new ones from scratch. This article will explain how to append lines to a file in Linux, including several subheadings and examples.

Using echo command

The easiest way to append new lines to a file is by using echo command. echo command allows you to display a message on screen, but it can also redirect message to a file. Here’s how to use echo command to append new lines to a file −

$ echo "New line of data" >> filename.txt

The «>>» symbol appends new line of data to end of file. If file does not exist, echo command will create a new file.

Using cat command

The cat command is another way to append new lines to a file. cat command is used to concatenate files, but it can also be used to append new lines to a file. Here’s how to use cat command to append new lines to a file −

$ cat > filename.txt New line of data EOF

Using tee command

The tee command is another way to append new lines to a file. tee command is used to display output on screen and also redirect it to a file. Here’s how to use tee command to append new lines to a file −

$ echo "New line of data" | tee -a filename.txt

The «-a» option tells tee command to append new line of data to end of file. If file does not exist, tee command will create a new file.

Using printf command

The printf command is another way to append new lines to a file. printf command is used to format and print data, but it can also redirect output to a file. Here’s how to use printf command to append new lines to a file −

$ printf "New line of data
" >> filename.txt

The «
» symbol tells printf command to create a new line.

Using sed command

The sed command is a powerful tool for manipulating text in Linux. sed command can also be used to append new lines to a file. Here’s how to use sed command to append new lines to a file −

$ sed -i '$aNew line of data' filename.txt

The «-i» option tells sed command to edit file in place. «$» symbol tells sed command to append new line of data to end of file.

Using awk command

The awk command is another powerful tool for manipulating text in Linux. awk command can also be used to append new lines to a file. Here’s how to use awk command to append new lines to a file −

The «BEGIN» symbol tells awk command to execute following command before reading input. «print» command tells awk command to print new line of data.

In addition to methods discussed above, there are other ways to append lines to a file in Linux that are worth exploring. Here are some other options −

Using file redirection operator

The file redirection operator «> >» is used to append new lines to a file in Linux. Here’s how to use it −

Where «command» is command whose output is to be appended to «file». For example, to append output of «ls» command to a file called «file.txt», you would use following command −

Using paste command

The paste command is used to merge lines of files. However, it can also be used to append new lines to a file. Here’s how to use paste command to append new lines to a file −

$ paste -s -d'
' file.txt - >> new_file.txt

The «-s» option tells paste command to merge lines. «-d» option specifies delimiter to use when merging lines. In this case, delimiter is a newline character. «-» symbol tells paste command to read input from standard input. «>>» symbol appends output to end of file.

Using ed command

The ed command is a line editor that can be used to edit files in Linux. Here’s how to use ed command to append new lines to a file −

$ echo "a" >> filename.txt $ echo "New line of data" >> filename.txt $ echo "." >> filename.txt $ ed filename.txt 
The "a" command tells ed command to enter append mode. "wq" command tells ed command to write changes to file and quit.
Conclusion
Appending new lines to a file in Linux is a common task for users and developers alike. There are several ways to append new lines to a file, including echo, cat, tee, printf, sed, and awk commands. Each command has its own advantages and disadvantages, so it is important to choose right command for job. By mastering techniques outlined in this article, you will be able to append new lines to files in Linux with ease, improving your productivity and efficiency.
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How to append multiple lines to a file
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 
 
10 Answers 10
 
# possibility 1: echo "line 1" >> greetings.txt echo "line 2" >> greetings.txt # possibility 2: echo "line 1 line 2" >> greetings.txt # possibility 3: cat > greetings.txt line 1 line 2 EOT # possibility 4 (more about input than output): arr=( 'line 1' 'line 2' ); printf '%s\n' "$" >> 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  
 
@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
 
echo -e "Hello \nWorld \n" >> greetings.txt 
 
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.
 
Another approach is to use tee
 
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.
 
 
+1 tee tends to work with paths that require sudo (solutions that use > >> < 
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 
 
It is worth to note that this variant is part of the ShellCheck recommendation github.com/koalaman/shellcheck/wiki/SC2129
 
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.
 
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 ' <> \;
 
I used the above example to insert the ending html tag that was missing on every html page within a number of directories.
 
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How to append output to the end of a text file
 
If file_to_append_to does not exist, it will be created.
 
$ echo "hello" > file $ echo "world" >> file $ cat file hello world 
 
The problem is that echo removes the newlines from the string. How do you append to a file a string which contains newlines?
 
echo does not remove newlines from the string. If you fail to properly quote the argument, then the shell will split the string and pass arguments to echo and echo never even sees the newlines.
 
@Pmpr note that echo is not part of the solution, it is only part of the example I typed, and there are no escape sequences in the example.
 
echo "hello world" >> read.txt cat read.txt echo "hello siva" >> read.txt cat read.txt 
 
then the output should be
 
hello world # from 1st echo command hello world # from 2nd echo command hello siva 
 
echo "hello tom" > read.txt cat read.txt 
 
You can use the >> operator. This will append data from a command to the end of a text file.
 
echo "Hi this is a test" >> textfile.txt 
 
Do this a couple of times and then run:
 
You'll see your text has been appended several times to the textfile.txt file.
 
Use command >> file_to_append_to to append to a file.
 
For example echo "Hello" >> testFile.txt
 
CAUTION: if you only use a single > you will overwrite the contents of the file. To ensure that doesn't ever happen, you can add set -o noclobber to your .bashrc .
 
This ensures that if you accidentally type command > file_to_append_to to an existing file, it will alert you that the file exists already. Sample error message: file exists: testFile.txt
 
Thus, when you use > it will only allow you to create a new file, not overwrite an existing file.
 
Using tee with option -a (--append) allows you to append to multiple files at once and also to use sudo (very useful when appending to protected files). Besides that, it is interesting if you need to use other shells besides bash, as not all shells support the > and >> operators
 
echo "hello world" | sudo tee -a output.txt 
 
This thread has good answers about tee
 
Use the >> operator to append text to a file.
 
I often confuse the two. Better to remember through their output:
 
> for Overwrite
 
$ touch someFile.txt $ echo ">" > someFile.txt $ cat someFile.txt > $ echo ">" > someFile.txt $ cat someFile.txt > 
 
>> for Append
 
$ echo ">" > someFile.txt $ cat someFile.txt > $ echo ">" >> someFile.txt $ cat someFile.txt >> 
 
this will append 720 lines (30*24) into o.txt and after will rename the file based on the current date.
 
Run the above with the cron every hour, or
 
while : do cmd >> o.txt && [[ $(wc -l  
 
I would use printf instead of echo because it's more reliable and processes formatting such as new line \n properly.
 
This example produces an output similar to echo in previous examples:
 
printf "hello world" >> read.txt cat read.txt hello world 
 
However if you were to replace printf with echo in this example, echo would treat \n as a string, thus ignoring the intent
 
printf "hello\nworld" >> read.txt cat read.txt hello world 
 
I'd suggest you do two things:
 
 
Use >> in your shell script to append contents to particular file. The filename can be fixed or using some pattern.
 
Setup a hourly cronjob to trigger the shell script
 
 
For example your file contains : 
 
 1. mangesh@001:~$ cat output.txt 1 2 EOF 
 
if u want to append at end of file then ---->remember spaces between 'text' >> 'filename'
 
 2. mangesh@001:~$ echo somthing to append >> output.txt|cat output.txt 1 2 EOF somthing to append 
 
And to overwrite contents of file :
 
 3. mangesh@001:~$ echo 'somthing new to write' > output.tx|cat output.tx somthing new to write 
 
This is misleading in many details. Spaces are not important and piping an empty output to cat is . just completely wacky. (It's empty because you just redirected standard output to a file.)
 
In Linux, You can use cat command to append file content to another file
 
In the previous command you will append content of fileName_1.txt to fileName_2.txt .
 
In Windows OS you can use type command
 
 
type fileName_1.txt >> fileName_2.txt
 
 
While all of these answers are technically correct that appending to a file with >> is generally the way to go, note that if you use this in a loop when for example parsing/processing a file and append each line to the resulting file, this might be much slower then you would expect.
 
A faster alternative might be this:
 
stringBuilder="" while read -r line; do # $'\n' prints a newline so we don't have to know what special chars the string contains stringBuilder+="$line"$'\n' done < "myFile.txt" echo "$stringBuilder" >$file 
 
WARNING: you are reading all lines into memory; memory is a limited resource, so don't go doing this for gigantic files.
 
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