[Linux-Discussion] Re: what does the variable $1 mean in Bourne shell?
- From: "Damian Scott" <sdamian@xxxxxxxxxx>
- To: linux-discussion@xxxxxxxxxxxxx
- Date: Tue, 18 Dec 2001 17:16:10 -0800
One other thing you can use is $*. That way you're not restricting your
self to any limited number of arguments you can use.
-Damian
"David Bruce Jr" <dbartbruce@xxxxxxxx>
Sent by: linux-discussion-bounce@xxxxxxxxxxxxx
12/18/01 04:02 PM
Please respond to linux-discussion
To: <linux-discussion@xxxxxxxxxxxxx>
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Subject: [Linux-Discussion] Re: what does the variable $1 mean
in Bourne shell?
Thanks,
now that you mention it I do remember that stuff about $1 is a variable
for
what
the user puts in the first argument and $2 is a varable for what the user
put in as the
second argument...
is that correct? sorta like a 'place holder'
-----------------
man pages are almost gibberish
lemme see, so if:
! Expands to the process ID of the most recently executed background
(asynchronous) command.
then $! means a variable assigned to the most recently backgrounded
command?
I'm trying to figure out our class project:
Write a shell script that does X, but first make sure the file exists
I'm working on the 'does the file exist or not' part.
an example from the text book is:
# Check for existance of file:
ls "$file" 2> /dev/null | grep "$file" > /dev/null
if [ $? != 0 ]
then
echo "$file not found" 1>&2
exit 1
I get the ls the file and if its not there send the err msg to /dev/null
then pipe it to grep (and I get kinda lost there)
if test (using brackets instead of the test command) and I get
completely lost
what is $? !=0
I've no clue
thanks
David
----- Original Message -----
From: "Brian L. Johnson" <blj8@xxxxxxxx>
To: <linux-discussion@xxxxxxxxxxxxx>
Sent: Tuesday, December 18, 2001 6:38 PM
Subject: [Linux-Discussion] Re: what does the variable $1 mean in Bourne
shell?
>
> 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!
> ---------------------------------
> For PGP key email to: pgpkey@xxxxxxxx
> For Geekcode email to: geekcode@xxxxxxxx
>
>
>
>
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