Using parameter and variable expansion
A $ followed by a number stands for a positional parameter
passed to the script or function. A positional parameter is represented
with either a single digit (except 0) or two or more digits in braces;
for example, 7 and {15} are both valid representations of positional
parameters. For example, if the command:
echo $1Similarly, a $ followed by the name of a shell variable (such as $HOME) stands for the value of the variable.
These constructs are called parameter expansions. In this sense, the term parameter can mean either a positional parameter or a shell variable.
The tcsh shell also supports more complicated forms of parameter expansions, letting you obtain only part of a parameter value or a modified form of the value.
| Modifier | Description | ||
|---|---|---|---|
| r | Root of value | ||
| e | Extension of value | ||
| h | Head of value | ||
| t | Tail of value |
For example, to extract only part of a file name, you can add one of these modifiers as follows:
| File name | r | e | h | t |
|---|---|---|---|---|
| /usr/bin/vi.txt | /usr/bin/vi | txt | /usr/bin | vi.txt |
| /u/bobby/mail | /u/bobby/mail | empty | /u/bobby | |
| storybook.pdf | storybook | empty | storybook.pdf | |
| INSTALL | INSTALL | empty | empty | INSTALL |