Re: Need mentorship and support
De: "Himanshu Shekhar" <irm2015006@iiita.ac.in>
> Also, I would love to know about good sources to learn and practice
> Bash. I followed "The Linux Command Line by William E. Shotts".
Chris F A Johnson has written two books on the subject. Haven't
read them but he used to be a regular on comp.unix.shell and he
seems to know what he's talking about.
/Shell Scripting Recipes: A Problem-Solution Approach/
http://cfajohnson.com/books/cfajohnson/ssr/
/Pro Bash Programming: Scripting the GNU/Linux Shell/
http://cfajohnson.com/books/cfajohnson/pbp/
> > 6) Lots of variable references without double quotes around them,
> > EG when calling configure_apt(). What if, say, the password
> > contains white space or "?" or "*" or "[" ?
>
> Please tell me about how to read special characters as @, ? etc. in
> password, as @ is the point after authentication where IP starts.
I'm not sure I understand the question. I don't expect read to
have problems with occurrences of "@" or "?" in its input (but
see its -r option).
The problem is not stuffing shell metacharacters into a
variable, it's what happens when you reference that variable.
Suppose variable v contains "*" (an asterisk). Compare the
output of
echo "$v"
and that of
echo $v
Or set v to "a b" then contrast the result of
mkdir "$v"
with
mkdir $v
The explanation is that when you write a command line like
cmd $v
the shell splits the value of v into words, performs pathname
expansion on each word and uses the result of that as the
arguments to cmd. You might intend to pass one argument to cmd
but you may end up passing zero, two or a thousand.
Sometimes, that is what you want. But usually what you want is
to pass one argument equal to the value of v. The syntax for
that is :
cmd "$v"
This also applies to constructs like if [ condition ]. When
someone writes
if [ $variable = "constant" ]
there's a high probability that he or she really means
if [ "$variable" = constant ]
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