How ToLatest

How to Use the wc Command in Linux

Linux laptop showing a bash prompt
fatmawati achmad zaenuri/

Counting the number of lines, words, and bytes in a file is useful, but the real flexibility of the Linux wc command comes from working with other commands. Let’s take a look.

What Is the wc Command?

The wc command is a small application. It’s one of the core Linux utilities, so there is no need to install it. It’ll already be on your Linux computer.

You can describe what it does in a very few words. It counts the lines, words, and bytes in a file or selection of files and prints the result in a terminal window. It can also take its input from the STDIN stream, meaning the text you want it to process can be piped into it. This is where wc really starts to add value.

It is a great example of the Linux mantra of “do one thing and do it well.” Because it accepts piped input, it can be used in multi-command incantations. As we’ll see, this little standalone utility is actually a great team player.

One way I use wc is as a placeholder in a complicated command or alias I’m cooking up. If the finished command has the potential to be destructive and delete files, I often use wc as a stand-in for the real, dangerous command.

That way, during the development of the command I get visual feedback that each file is being processed as I expected. There’s no chance of anything bad happening while I’m wrestling with the syntax.

As simple as wc is, there are still a few small quirks that you need to know about.

Getting Started With wc

The simplest way to use wc is to pass the name of a text file on the command line.

wc lorem.txt

Using wc with a file with one long line of text

This causes wc to scan the file and count the lines, words, and bytes, and write them out to the terminal window.

Words are considered anything bounded by whitespace. Whether they are words from a real language or not is irrelevant. If a file contains nothing but “frd g lkj”, it still counts as three words.

Lines are sequences of characters terminated by either a carriage return or the end of the file. It doesn’t matter if the line wraps around in your editor or in the terminal window, until wc encounters a carriage return or the end of the file, it’s still the same line.

Our first example found one line in the entire file. Here’s the content of the “lorem.txt” file.

cat lorem.txt

The content of the file with one long line

All of that counts as a single line because there are no carriage returns. Compare this to another file, “lorem2.txt”, and how wc interprets it.

wc lorem2.txt
cat lorem2.txt

Using wc with a file with many lines

This time, wc counts 15 lines because carriage returns have been inserted into the text to start a new line at specific points. However, if you count the lines with text in them, you’ll see there are only 12.

The other three lines are blank lines at the end of the file. These contain only carriage returns. Even though there is no text in these lines, a new line has been started and so wc counts them as such.

We can pass as many files to wc as we like.

wc lorem.txt lorem2.txt

Using wc with two files

We get the statistics for each individual file and a total for all the files.

We can also use wildcards so that we can select matching files instead of explicitly named files.

wc *.txt *.?

Using wc with wildcards

The Command Line Options

By default, wc will display the lines, words, and bytes in each file. It’s the same as using the -l (lines) -w (words) and -c (bytes) options.

wc lorem.txt
wc -l -w -c lorem.txt

Using wc with the lines, words, and bytes options

We can specify which combination of figures we wish to see.

wc -l lorem.txt

wc -w lorem.txt

wc -c lorem.txt

wc -l -c lorem.txt

Using wc with combinations of options

Special attention should be paid to the last figure, generated by the -c (bytes) option. Many people mistake this as counting the characters. It actually counts bytes. The number of characters and the number of bytes might well be the same. But not always.

Let’s look at the contents of a file called “unicode.txt.”

cat unicode.txt

The content of a file containing a non-Latin character

It has three words and a non-Latin alphabet character. We’ll let wc process the file with its default setting of bytes, and we’ll do it again but request characters with the -m (characters) option.

wc unicode.txt
wc -l -w -m unicode.txt

Counting the bytes in a file and then counting the characters in the same file

There are more bytes than there are characters.

Let’s have a look at the hex dump of the file and see what’s going on. The hexdump command’s -C (canonical) option displays the bytes in the file in lines of 16, with their plain ASCII equivalent (if there is one) shown at the end of the line. If there is no corresponding ASCII character, a period “.” is shown instead.

hexdump -C unicode.txt

A hexdump of a short file with a non-Latin character

In ASCII, a hexadecimal value of 0x20 represents a space character. If we count three values in from the left, we see the next value is a space character. So the those first three values 0x62, 0x6f, and 0x79 represent the letters in “boy.”

Hopping over the 0x20, we see another set of three hexadecimal values: 0x63, 0x61, and 0x74. These spell out “cat.” Hopping over the next space character we see three more values for the letters in “dog.” These are 0x64, 0x5f, and 0x67.

Right behind the word “dog” we can see a space character 0x20, and five more hexadecimal values. The last two are carriage returns, 0x0a.

The other three bytes represent the non-Latin character, which we’ve ringed in green. It is a Unicode character, and it takes three bytes to encode it. These are 0xe1, 0xaf, and 0x8a.

So make sure you know what you’re counting, and that bytes and characters need not be the same. Usually, counting bytes is more useful because it tells you what is actually inside the file. Counting by characters gives you the number of things represented by the contents of the file.

RELATED: What Are Character Encodings Like ANSI and Unicode, and How Do They Differ?

Taking Filenames From a File

There’s another way to provide filenames to wc . You can put the filenames in a file, and pass the name of that file to wc. It opens the file, extracts the filenames, and processes them as if they had been passed on the command line. This allows you to store an arbitrary collection of filenames for re-use.

But there’s a gotcha, and it’s a big one. The filenames must be null terminated, not carriage return terminated. That is, after each filename there must be a null byte of 0x00 instead of the usual carriage return byte 0x0a.

You can’t open an editor and create a file with this format. Typically, files like this are generated by other programs. But, if you have such a file, this is how you would use it.

Here’s our file containing the filenames. Opening it in less shows you the strange “^@” characters that less uses to indicate null bytes.

less source-files-list.txt

A file in less that contains null bytes

To use the file with wc, we need to use --files0-from (read input from) option and pass in the name of the file containing the filenames.

wc ---files0-from=source-files-list.txt

wc processing the file of null terminated filenames

The files are processed exactly as though they were provided on the command line.

Piping Input to wc

A much more common, flexible, and productive way to send input to wc is to pipe the output from other commands into wc . We can demonstrate this with the echo command.

echo "Count this for me" | wc
echo -e "Count this\nfor me" | wc

Using echo to send input to wc

The second echo command uses the -e (escaped characters) option to allow escaped sequences like the “\n” newline formatting code. This injects a new line, causing wc to see the input as two lines.

Here’s a cascade of commands feeding their input from one to the other.

find ./* -type f | rev | cut -d'.' -f1 | rev | sort | uniq
  • find looks for files (type -f) recursively, starting in the current directory. rev reverses the filenames.
  • cut extracts the first field (-f1) by defining the field delimiter to be a period “.” and reading from the “front” of the reversed filename up to the first period it finds. We’ve now extracted the file extension.
  • rev reverses the extracted first field.
  • sort sorts them in ascending alphabetical order.
  • uniq lists unique entries to the terminal window.

The list of unique extensions in the current directory tree

This command lists all of the unique file extensions in the current directory and any subdirectories.

If we added the -c (count) option to the uniq command it would count the occurrences of each extension type. But if we want to know how many different, unique file extensions there are, we can drop wc as the last command on the line, and use the -l (lines) option.

find ./* -type f | rev | cut -d'.' -f1 | rev | sort | uniq | wc -l

Adding wc to count the unique extensions

RELATED: How to Use the Linux cut Command

And Finally

Here’s one last trick wc can do for you. It’ll tell you the length of the longest line in a file. Sadly, it doesn’t tell you which line it is. It just gives you the length.

wc -L taf.c

Getting the length of the longest line in a file with wc

Beware though, that tabs are counted as eight spaces. Viewed in my editor, there are three two-space tabs at the start of that line. Its real length is 124 characters. So the figure reported is artificially expanded.

I’d treat this function with a big pinch of salt. And by that I mean don’t use it. Its output is misleading.

Despite its quirks, wc is a great tool to drop into piped commands when you need to count all sorts of values, not just the words in a file.

RELATED: 37 Important Linux Commands You Should Know

Source link

Leave a Reply

Your email address will not be published. Required fields are marked *