[bash] How to append output to the end of a text file

How do I append the output of a command to the end of a text file?

This question is related to bash shell

The answer is


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

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 >> instead of > when directing output to a file:

your_command >> file_to_append_to

If file_to_append_to does not exist, it will be created.

Example:

$ echo "hello" > file
$ echo "world" >> file
$ cat file 
hello
world

I'd suggest you do two things:

  1. Use >> in your shell script to append contents to particular file. The filename can be fixed or using some pattern.
  2. Setup a hourly cronjob to trigger the shell script

Use the >> operator to append text to a file.


You can use the >> operator. This will append data from a command to the end of a text file.

To test this try running:

echo "Hi this is a test" >> textfile.txt

Do this a couple of times and then run:

cat textfile.txt

You'll see your text has been appended several times to the textfile.txt file.


for the whole question:

cmd >> o.txt && [[ $(wc -l <o.txt) -eq 720 ]] && mv o.txt $(date +%F).o.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 <o.txt) -eq 720 ]] && mv o.txt $(date +%F).o.txt
    sleep 3600
done

To append a file use >>

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

To overwrite a file use >

echo "hello tom" > read.txt
cat read.txt  

then the out put is

hello tom


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.


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
  >>

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