7.8. Command Substitution
When a command is enclosed in backquotes, it will be executed and its output returned. This process is called command substitution. It is used when assigning the output of a command to a variable or when substituting the output of a command within a string. All three shells use backquotes to perform command substitution.
Example 7.34.
1 $ name=`nawk –F: '{print $1}' database`
$ echo $name
Ebenezer Scrooge
2 $ set `date`
3 $ echo $*
Fri Oct 22 09:35:21 PDT 2004
4 $ echo $2 $6
Oct 2004
EXPLANATION
The nawk command is enclosed in backquotes. Command substitution is performed. The output is assigned to the variable name, as a string, and displayed. The set command assigns the output of the date command to positional parameters. Whitespace separates the list of words into its respective parameters. The $* variable holds all of the positional parameters. The output of the date command was stored in the $* variable. Each parameter is separated by whitespace. The second and sixth parameters are printed.
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