Confuse how to use "$1" vs "$@" Post: 302924318

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Homework and Emergencies Homework & Coursework Questions Confuse how to use "$1" vs "$@" Post 302924318 by Scott on Friday 7th of November 2014 05:28:04 PM

11-07-2014

Administrator Emeritus

$1 represents the first positional parameter, and $@ represents all of them.

Here's an extract from the bash manual page on my system:

Code:

Positional Parameters
A positional parameter is a parameter denoted by one or more digits, other than the single digit 0. Positional
parameters are assigned from the shell's arguments when it is invoked, and may be reassigned using the set
builtin command. Positional parameters may not be assigned to with assignment statements. The positional
parameters are temporarily replaced when a shell function is executed (see FUNCTIONS below).

When a positional parameter consisting of more than a single digit is expanded, it must be enclosed in braces
(see EXPANSION below).

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).

Scott

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shift

SHIFT(P)						     POSIX Programmer's Manual							  SHIFT(P)

NAME

       shift - shift positional parameters

SYNOPSIS

       shift [n]

DESCRIPTION

       The  positional	parameters  shall  be shifted. Positional parameter 1 shall be assigned the value of parameter (1+n), parameter 2 shall be
       assigned the value of parameter (2+n), and so on. The parameters represented by the numbers "$#" down to "$#-n+1" shall be unset,  and  the
       parameter '#' is updated to reflect the new number of positional parameters.

       The  value  n  shall  be  an unsigned decimal integer less than or equal to the value of the special parameter '#' .  If n is not given, it
       shall be assumed to be 1. If n is 0, the positional and special parameters are not changed.

OPTIONS

       None.

OPERANDS

       See the DESCRIPTION.

STDIN

       Not used.

INPUT FILES

       None.

ENVIRONMENT VARIABLES

       None.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       Not used.

STDERR

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

       The exit status is >0 if n>$#; otherwise, it is zero.

CONSEQUENCES OF ERRORS

       Default.

       The following sections are informative.

APPLICATION USAGE

       None.

EXAMPLES

	      $ set a b c d e
	      $ shift 2
	      $ echo $*
	      c d e

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Special Built-In Utilities

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and  the  original  IEEE
       and  The  Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								  SHIFT(P)