Working with files and folders

• Working with files and folders
  • Reading Files
    • less
    • cat
    • head
    • tail
  • Creating, Removing, Copying, and Moving Files and Directories
    • Make a Directory with mkdir
    • Make a File with touch
    • Remove Files and Folders with rm
      • Watch out
      • Remove a File
      • Remove a file and ask
    • Copying with cp
    • Moving with mv
  • Bundling with tar
    • tar flags
    • uncompressed bundling
    • compressed bundling
    • Extracting a Compressed tar file

Reading Files

less

less is used to read files.
With a linux terminal pwd at /home/ubuntu, and a text file in the directory (noted in a previous page) called something like newfile.txt less can be used to read the file with less newfile.txt.

...I don't use less to read files. I usually use cat or tail depending on the need to read the file. I've heard less is a more robust file reader, but for longer reads I usually open a text-editor like vscode. To check out more details on less see the help less --help or read the manual with man less.

cat

cat reads the file && prints its contents to the screen.
cat newfile.txt will print the entire newfile.txt to the terminal output.

head

head takes the first bunch of lines of a files && prints them to the termial. By default, head prints 10 lines.

tail

tail takes the last bunch of lines of a files && prints them to the termial. By default, tail prints 10 lines.
This tail command can be useful for inspecting a file that captures application log activity. tail -f the-log-file.txt will aid in reviewing application logs as the logs are occuring in real-time.
The -f flag means "follow", and using tail -f the-log-file.txt will "follow" new contents being added to said log file and print the new contents, as they appear, in the terminal output.

Creating, Removing, Copying, and Moving Files and Directories

Make a Directory with mkdir

mkdir makes a directory.
mkdir this-new-dir will make a new directory called this-new-dir.

mkdir -p one/two/three leverage the "-p" flag, which represents "parent", to create all subdirectories needed.
Here, directory one is a parent of two, two is a child of one and a parenet of three, and three is a child of two.

Make a File with touch

touch can be used to create a file.
touch new-file-who-dis.txt will create the file new-file-who-dis.txt.
NOTE: running touch on a file that already exists updates the last-modified date and last-accessed date.

Remove Files and Folders with rm

Watch out

We might be used to the are you sure type messages when deleting content from apps.
Here, though, watch out. Those types of alerts usually need to be manually triggered, and running rm will most likely delete everything without a confirmation request unless you tell the command to ask you for permission.

Remove a File

With the terminal at the directory of /home/ubuntu where ls reveals a file called newfile.txt,
run rm newfile.txt.
Notice nothing seems to happen.
Run ls and see that the newfile.txt is gone. Forever. No whoops I forgot do to that here.

Remove a file and ask

Create a new file called asdf.txtby using touch asdf.txt. We will use this to delete the file.
rm -i asdf.txt will prompt for your approval:

ubuntu@primary:~$ rm -i asdf.txt 
rm: remove regular empty file 'asdf.txt'?

Copying with cp

cp is used to copy stuff.
cp originalFile.txt destination-file.txt will copy originalFile.txt to destination-file.txt.
cp init.txt new-dir/ will copy init.txt to a new directory called new-dir.
cp -R this-dir that-dir will copy the this-dir directory into a new directory that-dir.

Moving with mv

mv this.txt that.txt will "move" the this.txt to a new file called that.txt. This is sort of like re-naming the file here.
Maybe a more common use could be mv this.txt dir/this.txt.

Bundling with tar

tar is used to put files together.

tar flags

Tar has a lot of flags. Here's some more common ones for the infrequent tar users:

• -c: create a tar archive, short for --create
• -f: use an archive file, short for --file=ARCHIVE
• -z: put the tar archive through gzip compression
  Those 3 flags together are often used as -cfz to bundle a file in a compressed format.
• -x: extract files from an archive

The -x flag is often combined with other flags to decompress and "untar" a compressed + tarred file.

uncompressed bundling

Lets bundle 3 things:

• a file called qwer.txt
• a directory called dir
• a file in the dir directory called asdf.txt This will get bundled into a tar filed called uncompressed.tar.

The command to do this looks like

tar -cf uncompressed.tar qwer.txt dir

Revealing the file using ls will show uncompressed.tar.

compressed bundling

Noted above is a single flag to add, the -z flag.
The name of the bundled tarfile here will change to compressed.tar.gz. The gz is common to allude to the compressed nature of the file.

The command to do this looks like

tar -cfz compressed.tar.gz qwer.txt dir

Revealing the file using ls will show compressed.tar.gz.

Extracting a Compressed tar file

# create the new location
mkdir untarred

# un-tar the compressed file
tar -xfz compressed.tar.gz -C untarred/

Notice that the 3 flags to tar+compress the compressed file are -cfz and the 3 flags to untar+uncompress the file are -xfz.
These are nearly identical. the -c and the -x are exchanged, -c for compressing and -x for extracting