of the shell program
To show these built-in variables in use, here is a sample program called mypgm2:
#!/bin/sh
#my test program
echo 'Number of parameters is $#'
echo 'Program name is $0'
echo 'Parameters as a single string is $*'
If you execute mypgm2 from the command line in bash as follows
$ bash mypgm2 Andrew Hudson
you get the following result:
Number of parameters is 2
Program name is mypgm2
Parameters as a single string is Sanjiv Guha
Special Characters
Some characters have special meaning to Linux shells; these characters represent commands, denote specific use for surrounding text, or provide search parameters. Special characters provide a sort of shorthand by incorporating these rather complex meanings into a simple character. Table 33.1 shows some special characters.
TABLE 33.1 Special Shell Characters
| Character | Explanation |
|---|---|
$ | Indicates the beginning of a shell variable name |
| | Pipes standard output to next command |
# | Starts a comment |
& | Executes a process in the background |
? | Matches one character |
* | Matches one or more characters |
> | Output redirection operator |
< | Input redirection operator |
` | Command substitution (the backquote or backtick — the key above the Tab key on most keyboards) |
>> | Output redirection operator (to append to a file) |
<< | Wait until following end-of-input string (HERE operator) |
[ ] | Range of characters |
[a-z] | All characters a through z |
[a,z] or [az] | Characters a or z |
| Space | Delimiter between two words |
Special characters are very useful to you when you are creating shell scripts, but if you inadvertently use a special character as part of variable names or strings, your program behaves incorrectly. As you learn in later parts of this section, you can use one of the special characters in a string if you precede it with an /, or backslash) to indicate that it isn't being used as a special character and shouldn't be treated as such by the program.
A few special characters deserve special note. They are the double quotes ('), the single quotes ('), the backslash (), and the backtick (`) — all
