[Linux-Discussion] Re: what does the variable $1 mean in Bourneshell?
- From: "Brian L. Johnson" <blj8@xxxxxxxx>
- To: linux-discussion@xxxxxxxxxxxxx
- Date: Tue, 18 Dec 2001 16:38:18 -0700 (MST)
On Dec 18, David Bruce Jr did the finger mambo upon the keyboard:
>$1 means "assign this value to a variable, so later on in the shell script
>all you
>gotta do is use $1 and you don't have to write the whole file name"
>I think
Well, yes and no... $1, $2, etc are variables, but are special ones used
to represent the commandline parameters. So if you run a script like
this:
scriptfile.sh bat box fruit ball car
$1 would be "bat"
$2 would be "box"
etc...
As for "$?":
(From the man page for Bash)
* 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 null or unset, the parameters are separated by
spaces.
@ Expands to the positional parameters, starting from
one. When the expansion occurs within double
quotes, each parameter expands as a separate word.
That is, `` $@'' is equivalent to ``$1'' ``$2'' ...
When there are no positional parameters, ``$@'' and
$@ expand to nothing (i.e., they are removed).
# Expands to the number of positional parameters in
decimal.
? Expands to the status of the most recently executed
foreground pipeline.
- Expands to the current option flags as specified
upon invocation, by the set builtin command, or
those set by the shell itself (such as the -i
flag).
$ Expands to the process ID of the shell. In a ()
subshell, it expands to the process ID of the cur=AD
rent shell, not the subshell.
! Expands to the process ID of the most recently exe=AD
cuted background (asynchronous) command.
0 Expands to the name of the shell or shell script.
This is set at shell initialization. If bash is
invoked with a file of commands, $0 is set to the
name of that file. If bash is started with the -c
option, then $0 is set to the first argument after
the string to be executed, if one is present. Oth=AD
erwise, it is set to the pathname used to invoke
bash, as given by argument zero.
_ Expands to the last argument to the previous com=AD
mand, after expansion. Also set to the full path=AD
name of each command executed and placed in the
environment exported to that command.
-=3DBrian L. Johnson, www.blj8.com=3D-
9136 links at blj8.com!
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