Creating files and directories

For creating files, touch is used. This tool is also used to change the timestamp of the file (or reset it). For example with the -t flag touch -t 12092018 myfile sets the date of myfile to the 9/12/2018
Directories are created with mkdir

Creating files with content

For this, there is two options from the command line:

Use a text editor

Use a command:

echo together with write and append redirection

 echo line one > file1
 echo line two >> file2    

cat together with redirection

cat << EOF > file1
line one
line two
EOF

Removing

Removing a directory is done with rmdir. The directory must be empty
To remove a directory and all of its contents rm -rf.
rm Removes a file (Also accepts patterns). Has additional options, for example –f to forcefully remove a file or –i to interactively remove it(prompt every time)

Moving and renaming

For files and directories both can be done with the mv command.

mv file other_file changes the file name
mv file dir/dir/ moves the file
mv file dir/dir/other_file moves the file and changes the name

Viewing files

cat Prints file content to screen
tac Same as cat but starts from the bottom up
less Used to view larger files because it is a paging program (Add scrolling). Special options can be used to search for patterns (/ for forward and ? backwards)
tail Print the last 10 lines of a file (with the -n flag or -15 the number can be changed)
head Print the first 10 lines of a file (with the -n flag or -15 the number can be changed)

Search files

Wildcards

Basic search commands (and ls, among others) allow for the use of wildcards to search for files:

? Matches any character
* Matches any string (E.g *.doc would match all .doc files)
[abc] Matches any character inside the brackets (- can be used for ranges)
[!abc MAtches any character except the ones in brackets

`locate`

Performs a search taking advantage of a previously constructed database of files and directories on your system.
Matches all entries that contain a specified character string.
The database is constructed with updatedb. (Automatic in most linux distros once a day, can be run manually).
Can be piped with grep to further filter the results
Does not come in Ubuntu 19+ by default

`find`

Recurses down the filesystem tree from any particular directory (or set of directories) and locates files that match specified conditions.
The default pathname is always the present working directory.

Different flags can be used (See man find):

  find . -name wa #Finds files and directories named wa
  find . -iname wa #Ignore case in the name matching
  find . -type d -name wa #Only directories
  find . -type f -name wa #Only files

Also allows to directly process the results using the -exec option. Uses {} as placeholder for the results. (-ok can also be used to prompt every operation)
```
  find -name "*.swp" -exec rm {} ';' #Finds and removes all .swp files  
```
Other tests to match include
- ctime n When the inode metadata last changed (When it was created) (n is the number of days, can also be +n for bigger than and -n)
- atime n Accessed/Last Read time
- mtime n Modified/Last Written time
- cmin amin mmin Same but in minutes
- size nU Size of the file, n is the size (can also be +n o -n) and U is the unit (by default 512 bytes blocks, k for kilobytes, M for megabytes, G for gigabytes).