Example 02: The Shell

We start in the home directory for this seminar’s website:

pwd

ls

Make a temporary directory:

mkdir tmp

touch and cat

Use touch to create an empty file:

touch tmp/my-file.txt

List it:

ls -l tmp

Echo some text into some files:

echo Hello > tmp/01-my-file.txt
echo There > tmp/02-my-file.txt

ls -l tmp

Cat the files

cat tmp/01-my-file.txt tmp/02-my-file.txt

Cat the files into a new file:

cat tmp/01-my-file.txt tmp/02-my-file.txt > tmp/03-my-file.txt

cat tmp/03-my-file.txt

Append to a file with >> instead of >:

cat tmp/01-my-file.txt tmp/02-my-file.txt >> tmp/03-my-file.txt

Result:

cat tmp/03-my-file.txt

Brace expansion

You can do this:

#| class: scrollout

touch tmp/{a..z}.txt

ls tmp/

Or this:

#| class: scrollout

touch tmp/{A..Z}{0..10}.txt

ls tmp/

A loop

You can write loops in the shell as well:

for f in {a..z}{0..10}
do
    echo hello > "tmp/$f.txt"
done

#| class: scrollout
ls tmp/

cat tmp/u3.txt

Using cut

We can cut files or STDIN. Here we get a long listing of the files in a directory, cut the output using whitespace as the field delimiter (-w), select fields 6 and 7 (-f6-7) which are the modification dates of the file and then get the unique values with a count of their frequency.

ls -lt assets/01-file-system/ | cut -w -f6-7 | uniq -c

Clean up

The rm command is dangerous!

The rm command deletes the named files. rm -f forces the deletion without any further confirmation. The -r switch deletes files and directories recursively starting from the top level directory provided and descending into every directory below. The combination of the -r and -f switches makes it easy to accidentally delete way too much.

## Be VERY CAREFUL with the syntax of this command
rm -rf tmp/