command argument1 argument2 ... argumentArguments
Arguments in Unix/Linux commands are values or data passed to commands for processing. Unlike options, which modify the behavior of commands, arguments typically specify what the command should act upon. This typically includes filenames, user names, data values, or other kinds of information the command needs to execute its task.
Anatomy
A Unix command can be broken down into the command name, followed by its options (which we’ll address in the next chapter), and then its arguments:
Argument Types
Below are a variety of command arguments types. This is not an exhaustive list, but includes many of the commands and arguments you’ll encounter on a regular basis.
Direct arguments
Direct arguments are the most straightforward type of arguments. They are typically the names of files or directories on which commands operate.
Example
In the command cat my_file.txt, my_file.txt is a direct argument to the cat command, telling it which file to display on the standard output.
cat my_file.txt
# This is my fileIndirect arguments
Indirect arguments are arguments that might specify additional information that commands need to complete their tasks.
Example
The file search pattern for the grep command is an example of an indirect command, and myfile.txt is the direct argument.
grep file my_file.txt
# This is my fileMost commonly, arguments are the names of files and directory names on which the command will operate.
Example
my_file.txt and tmp/tmp_file.txt are arguments representing the source and destination locations to move with mv, respectively.
mv my_file.txt tmp/tmp_file.txtCommands related to user management might take user and group names names as arguments.
Example
chown changes the ownership of file to user and group.
chown user:group myfile.txtCommand Targets
Some commands take other commands as arguments.
Example
For example, sudo command runs command with superuser privileges.
sudo vi path/to/file.configData Values
Commands might take data values as arguments for processing.
Example
In echo Hello, World!, Hello, World! is the argument value that echo prints to the terminal.
echo Hello, World!
# Hello, World!Order and Position
For many commands, the order of the arguments is significant.
Example
tmp/tmp_file.txt is the first argument (indicating the file to copy from), and new_file.txt is the second argument (indicating where to copy the file to).
cp tmp/tmp_file.txt new_file.txtReversing these arguments would result in a completely different operation.
Arguments that contain spaces must be quoted or escaped, so the shell understands them as a single argument rather than multiple arguments.
Example
To copy the contents of the new new_file.txt to 'my new file.txt', you would use:
cp new_file.txt 'my new file.txt'Command Substitution
The output of a command can be used as an argument for another command using backticks (` `) or $( ).
Example
echo $(grep file 'my file 2.txt') uses the output of the grep command as an argument for echo:
echo $(grep file 'my new file.txt')
# This is my fileVariables as Arguments
Environment variables can be used as arguments in commands.
Example
echo $HOME prints the path to the user’s home directory, where $HOME is an argument that the echo command interprets:
echo $HOME
# /Users/usernameRecap
Understanding the nuances of Unix arguments is crucial for crafting precise and effective commands, allowing users to leverage the full power of the Unix command line for a wide array of tasks.