Read
head, cat, less, and tail¶
Now that we know what files exist on our computer, it's time to look at the contents of the file. There are multiple ways to look at the contents of a file.
The cat command prints the entirety of a file to the stdout of our computer. We can scroll through files using the less command. Less is a safe way of looking at the contents of a file without the ability to change it. head prints, by default, the first 10 lines of a file and tail prints the last 10 lines.
All four of the commands use the same syntax:
head [filename]
cat [filename]
less [filename]
tail [filename]
Tip
You can use TAB to do filename completion, so if you type cat R and then press your TAB key once, it will autocomplete if there is a unique match. If there is more than one match, the first TAB will do nothing, and the second will show all the possible matches.
Let's navigate to the books directory and use the head command to view the README.md file.
cd ~/books/
head README.md
You should see an output that looks like this. The README.md file is written in Markdown. To learn more about Markdown syntax, read this excellent Markdown guide.
# Books
These books were downloaded from [Project Gutenberg](https://www.gutenberg.org/ebooks/) using the following commands.
curl https://www.gutenberg.org/files/98/98-0.txt -o book.txt
curl https://www.gutenberg.org/files/98/98-0.txt -o A-tale-of-two-cities.txt
curl https://www.gutenberg.org/files/11/11-0.txt -o Alice_in_wonderland.txt
curl https://www.gutenberg.org/files/16/16-0.txt -o PeterPan.txt
curl https://www.gutenberg.org/files/55/55-0.txt -o WizardOfOz.txt
Now we can view the file with head, cat, or less and tail.
head book.txt
cat book.txt
less book.txt
tail book.txt
We can see there are several more books in the directory, and we can look at the first few lines of all the txt files with the *.
head *.txt
gunzip¶
Notice, there is one book that is compressed. We can uncompress it with the command gunzip.
gunzip WizardOfOz.txt.gz
Now the ls command will show that the WizardOfOz.txt.gz has been replaced with the unzipped WizardOfOz.txt file. gunzip also has a number of flags you can use including -k which will allow you to unzip the file and keep the original.
Key points¶
| Command [OPTION] | Description |
|---|---|
head [filename] |
print first 10 lines of FILENAME |
cat [filename] |
print FILENAME's contents to stdout |
less [filename] |
view FILENAME without printing to stdout |
tail [filename] |
print last 10 lines of FILENAME |
gunzip -k [filename] |
uncompress a file and keep the original |