meaning of the construction: ${1+"$@"} ? Post: 302489141

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Top Forums UNIX for Advanced & Expert Users meaning of the construction: ${1+"$@"} ? Post 302489141 by alex_5161 on Thursday 20th of January 2011 12:08:00 PM

01-20-2011

Registered User

Once again, Thanks ctsgnb for replay!
Appreciate to see your thoughts.
... some space or tab .. - OK, reasonable to apply the $@; so it would keep the word with spase as one word!
Good point!
Anything else is not a case, as I see it here: followed code (just couple line to set the 'prompt') have no relation to first 'cd' command; all other guesses are not reasonable in here (unless the code was used from some source where other your points could be meaningfull.)

I have check situation with a space and a new line in the dir-name. Here is the test-code and results:

Code:

> typeset -f tst
tst ()
{
    cdir=$(pwd);
    echo "starting in >${cdir}< directory.";
    echo "<"${1+$@}">";
    echo "\$@ is:"$@"<";
    \cd $@;
    echo "after \\cd \$@; now in $(pwd)";
    chdir $cdir;
    \cd ${1+$@};
    echo "after \\cd \${1+\$@}; now in $(pwd)";
    chdir $cdir;
    'cd' ${1+"$@"};
    echo "after 'cd' \${1+\"\$@\"}; now in $(pwd)";
    chdir $cdir;
    \cd "$@";
    echo "after \\cd \"\$@\"; now in $(pwd)";
    chdir $cdir
}
P> mkdir TST_dir "TST dir" "TST
> dir"
>
> tst TST_dir
starting in >/export/home/dca/TMP< directory.
<TST_dir>
$@ is:TST_dir<
after \cd $@; now in /export/home/dca/TMP/TST_dir
after \cd ${1+$@}; now in /export/home/dca/TMP/TST_dir
after 'cd' ${1+"$@"}; now in /export/home/dca/TMP/TST_dir
after \cd "$@"; now in /export/home/dca/TMP/TST_dir
> tst "TST dir"
starting in >/export/home/dca/TMP< directory.
<TST dir>
$@ is:TST dir<
bash: cd: TST: No such file or directory
after \cd $@; now in /export/home/dca/TMP
bash: cd: TST: No such file or directory
after \cd ${1+$@}; now in /export/home/dca/TMP
after 'cd' ${1+"$@"}; now in /export/home/dca/TMP/TST dir
after \cd "$@"; now in /export/home/dca/TMP/TST dir
> tst "TST
> dir"
starting in >/export/home/dca/TMP< directory.
<TST dir>
$@ is:TST dir<
bash: cd: TST: No such file or directory
after \cd $@; now in /export/home/dca/TMP
bash: cd: TST: No such file or directory
after \cd ${1+$@}; now in /export/home/dca/TMP
after 'cd' ${1+"$@"}; now in /export/home/dca/TMP/TST
dir
after \cd "$@"; now in /export/home/dca/TMP/TST
dir

So, by this testing the '\cd "$@" ' is completely suffisient. Most important, it is strait forward with nothing extra; no extra functionality, no questions.

Maybe anybody see anything else that would be a reason to have 'cd' ${1+"$@"} instead of the \cd "$@" ?

Thanks!

---------- Post updated 01-20-11 at 01:08 PM ---------- Previous update was 01-19-11 at 03:53 PM ----------

I have the answer from another place: here
and this question was discussed also here2

Shortly, that syntax provide appropriate 'cd' functionality with no-arguments when "$@" for no-arguments returned empty string, instead of 'nothing' (as it was 20 years ago.)
cd - with 'nothing' change to home-dir;
cd "" - with empty string stay in current dir (so, it is the >cd . )

But today the "$@" return correctly nothing and 'cd' will process "$@" appropriately.

alex_5161

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NAME

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SYNOPSIS

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DESCRIPTION

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OPTIONS

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EXAMPLE

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SEE ALSO

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