The Shell Game 153It says, “If there is at least one argument ( ${1+ ), then substitute in
all the arguments ( “$@” ) preserving all the spaces, etc. within each
argument.If we used only “$@” then that would substitute to “” (a null argu-
ment) if there were no invocation arguments, but we want no argu-
ments reproduced in that case, not “”.Why not “$*” etc.? From a sh(1) man page:Inside a pair of double quote marks (“”), parameter and
command substitution occurs and the shell quotes the results to
avoid blank interpretation and file name generation. If $* is
within a pair of double quotes, the positional parameters are
substituted and quoted, separated by quoted spaces (“$1
$2 ...”); however, if $@ is within a pair of double quotes, the
positional parameters are substituted and quoted, separated by
unquoted spaces (“$1” “$2” ...).I think ${1+“$@”} is portable all the way back to “Version 7 Unix.”Wow! All the way back to Version 7.
The Shell Command “chdir” Doesn’t
Bugs and apparent quirky behavior are the result of Unix’s long evolution
by numerous authors, all trying to take the operating system in a different
direction, none of them stopping to consider their effects upon one another.
Date: Mon, 7 May 90 22:58:58 EDT
From: Alan Bawden <[email protected]>
Subject: cd.. : I am not making this up
To: UNIX-HATERSWhat could be more straightforward than the “cd” command? Let's
consider a simple case: “cd ftp.” If my current directory,
/home/ar/alan, has a subdirectory named “ftp,” then that becomes my
new current directory. So now I’m in
/home/ar/alan/ftp. Easy.Now, you all know about “.” and “. .”? Every directory always has
two entries in it: one named “.” that refers to the directory itself, and
one named “. .” that refers to the parent of the directory. So in our
example, I can return to /home/ar/alan by typing “cd. .”.