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In a shell script file i saw "$*", what does it mean and when we have to use it?

Saeed Zarinfam
  • 5,507

2 Answers2

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From bash(1)…

Special Parameters

The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed.

* Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, it expands to a single word with the value of each parameter separated by the first character of the IFS special variable. That is, "$*" is equivalent to "$1c$2c…", where c is the first character of the value of the IFS variable. If IFS is unset, the parameters are separated by spaces. If IFS is null, the parameters are joined without intervening separators.

@ Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, each parameter expands to a separate word. That is, "$@" is equivalent to "$1" "$2" …. If the double-quoted expansion occurs within a word, the expansion of the first parameter is joined with the beginning part of the original word, and the expansion of the last parameter is joined with the last part of the original word. When there are no positional parameters, "$@" and $@ expand to nothing (i.e., they are removed).

Basically, $* is a special variable whose value is the script's (or shell function's) parameters. Most of the time, "$@" is more appropriate.

200_success
  • 5,535
1

This corresponds to all parameters passed to the script. In your example, it's surrounded in quotes; this is important as the quotes encapsulate the (presumably) whitespace between the parameters. Omitting the quotes in shell scripts can often be a source for bugs.

Here, in the case of bash, taken from the manpage:

 *      Expands to the positional parameters, starting from one.  When the expansion  occurs
          within  double  quotes, it expands to a single word with the value of each parameter
          separated by the first character of the IFS special  variable.   That  is,  "$*"  is
          equivalent  to  "$1c$2c...",  where c is the first character of the value of the IFS
          variable.  If IFS is unset, the parameters are separated by spaces.  If IFS is null,
          the parameters are joined without intervening separators.

cheers

sc.

swisscheese
  • 330