06-23-2015
Quote:
Originally Posted by
Don Cragun
Aia,
No, $123 does not expand to the value of the 123rd positional parameter; it expands to the value of the 1st positional parameter followed by the string 23. To get the 123rd positional parameter with a POSIX conforming shell, you would need to use ${123}. With a pure Bourne shell you can't reference any positional parameters after the 9th positional parameter directly without shifting away lower positional parameters.
And, expanding an undefined variable (including positional parameters) produces an empty string; not some undefined value.
Don,
Thank you for correcting that, somehow I forgot that normal variable names start with letters or underscore, thus my premises were wrong, since I was considering
abc$123 as the shell trying to interpret
abc$var
Quote:
which if it is not set it would be undefined
Just bad wording. I meant the variable does not exist. It is undeclared. The variable itself, not the value it can produce.
Last edited by Aia; 06-23-2015 at 09:29 PM..
Reason: Grammar
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shift(1) User Commands shift(1)
NAME
shift - shell built-in function to traverse either a shell's argument list or a list of field-separated words
SYNOPSIS
sh
shift [n]
csh
shift [variable]
ksh
* shift [n]
DESCRIPTION
sh
The positional parameters from $n+1 ... are renamed $1 ... . If n is not given, it is assumed to be 1.
csh
The components of argv, or variable, if supplied, are shifted to the left, discarding the first component. It is an error for the variable
not to be set or to have a null value.
ksh
The positional parameters from $n+1 $n+1 ... are renamed $1 ..., default n is 1. The parameter n can be any arithmetic expression that
evaluates to a non-negative number less than or equal to $#.
On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:
1. Variable assignment lists preceding the command remain in effect when the command completes.
2. I/O redirections are processed after variable assignments.
3. Errors cause a script that contains them to abort.
4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari-
able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not
performed.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
SEE ALSO
csh(1), ksh(1), sh(1), attributes(5)
SunOS 5.10 15 Apr 1994 shift(1)