More (advanced) commands.

Alias

You will often have to write the same command again and again. If it is a longer command, it is reducing your productivity having to repeat it. Then you can use the alias command to create an ‘alias’ for your command.

To see the currently definted aliases, execute the ‘alias’ command:

$ alias

Example

This is how it might look when you run alias:

b-an01 [~]$ alias
alias cdn='cat >/dev/null'
alias dir='ls -lAF'
alias l='dir'
alias ls='ls -F'

As an example, this means that if you type ‘dir’ the actual command that is executed is ‘ls -lAF’.

In order to create a new alias, you could write:

$ alias shortName="your custom command here"

Warning

The alias will only be valid in that shell, and only until you logout. Next time you will have to issue the ‘alias’ command again, unless you add it to either your .bashrc or .bash.profile file.

Adding a new alias to the .bashrc file, using ‘nano’ editor

  1. Open the file: nano ~/.bashrc

  2. Inside the editor, scroll down to where your aliases are. If you do not have any, just add them at the end, like this 

    #My custom aliases
alias c="clear"
alias ll="ls -alF"
# Colourize ls output
alias ls='ls --color=auto'
# Colourize grep output
alias grep='grep --color=auto'
# Easily list my SLURM batch jobs
alias jobs='squeue -u $USER'
# Find all entries starting with d in the output from the ls -lahrt command
alias ldir=’ls -lahrt | egrep "^d"’

  3. Save and Exit the file: CTRL-x (Press CTRL and hold it down while pressing x). Answer ‘Y’ to save.
  4. Next time you start a shell or after a new login your new alias is available. To make it available immediately, run 
    $ source ~/.bashrc

awk

Powerful, but somewhat more advanced command!

This command finds patterns in a file and can perform arithmetic/string operations. You can use it to transform data files and produce formatted reports.

It allows the user to use variables, numeric functions, string functions, and logical operators.

Things awk can do:

  • Scan a file line by line
  • Split each input line into fields
  • Compare input line/fields to pattern
  • Perform action(s) on matched lines

Search for the pattern ‘snow’ in the file FILE and print out the first column

awk '/snow/ {print$1}' FILE

Print column 3 and 4 from file mydata.dat

awk '{print $3 "\t" $4}' mydata.dat

Print column 2 and 3 from file mydata.dat, but only those rows that contain the letter ‘r’

awk '/r/ {print $2 "\t" $3}' mydata.dat

chown - change ownership

To change ownership of a file or directory, use the command chown.

chown [OPTIONS] USER[:GROUP] FILE(s)

Examples

  • chown USERNAME FILE the user with USERNAME becomes the new owner of FILE
  • chown USERNAME DIRECTORY the user with USERNAME becomes the new owner of DIRECTORY (but not any subdirectories)
  • chown USERNAME:folk DIRECTORY the user ownership is changed to USER and the group ownership to group “folk” for the directory DIRECTORY
  • chown :folk DIRECTORY the group ownership is changed to the group “folk” for the directory DIRECTORY
  • chown -R USERNAME:folk DIRECTORY the user ownership is changed to USERNAME and the group ownership is changed to group “folk” for the directory DIRECTORY and all subdirectories

Warning

As default, chown does not generate output on success and returns zero.