linux-concatenate-files

Linux provides us commands to perform various operations on files. One
such activity is the concatenation – or merging – of files.

In this quick tutorial, we’ll see how to concatenate files into a
single file.

To concatenate files, we’ll use the cat (short for concatenate)
command.

Let’s say we have two text files, A.txt and B.txt.

A.txt:

B.txt:

Now, let’s merge these files into file C.txt:

The cat command concatenates files and prints the result to the
standard output. Hence, to write the concatenated output to a file,
we’ve used the output redirection symbol ‘>’. This sends the
concatenated output to the file specified.

The above script will create the file C.txt with the concatenated
contents:

Note that if the file C.txt already exists, it’ll simply be
overwritten.

Sometimes, we might want to append the content to the output file rather
than overwriting it. We can do this by using the double output
redirection symbol >>:

The examples above concatenate two files. But, if we want to concatenate
more than two, we specify all these files one after another:

This’ll concatenate all the files in the order specified.

If the number of files to be concatenated is large, it is cumbersome to
type in the name of each file. So, instead of specifying each file to be
concatenated, we can use wildcards to specify the files.

For example, to concatenate all files in the current directory, we can
use the asterisk(*) wildcard:

We have to be careful while using wildcards if the output file already
exists — if the wildcard specified includes the output file, we’ll get
an error:

It’s worth noting that when using wildcards, the order of the files
isn’t predictable. Consequently, we’ll have to employ the method we saw
in the previous section if the order in which the files are to be
concatenated is important.

Going a step further, we can also use pipes to feed the contents of the
input files to the cat command. For example, we can echo the
contents of all files in the current directory and feed it’s output
to cat:

In this tutorial, we saw how easy it is to concatenate multiple files
using the Linux cat command.