loop through empty string

Question

Recently I found a part of code which confuses me:

typeset _Var=''

for _Var
do
   ... a command
done

can anyone explain how this loops through an empty list of values is working?

thanks a lot for any post.

The empty string in typeset _Var='' is a red herring. The for keyword will provide _Var with other values, explicit with the in keyword, or implicit with out. See below. — Henk Langeveld
– Henk Langeveld, Commented Dec 28, 2015 at 22:03
That’s because for x + newline(!) + do is equivalent to POSIX shell for x in "$@"; do. Note that you cannot use for x; do because some shells misparse that. Source: GNU autoconf texinfo manual, section about portable shell. — mirabilos
– mirabilos, Commented Dec 29, 2015 at 15:02

Henk Langeveld · Accepted Answer · 2015-12-28 21:58:04Z

2

The construct

for var
do
    echo something
done

without the in keyword will default to the list of positional parameters, e.g., $1, $2, etc.

So your script will execute the loop body once for each separate argument on the command line.

The snippet above invoked as ksh testscript a b c will output:

something
something
something

answered Dec 28, 2015 at 21:58

Henk Langeveld

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