Shell Programming and Scripting

Hello Community!
Let's say that we have some script which counts its arguments number:
arguments_count.sh:

Code:

#!/bin/sh
echo "Number of arguments="$#

and some test script:
test.sh:

Code:

#!/bin/sh
my_args="1 2 3 '4 5' 6"
echo "Count of arguments when using my_args:"
./arguments_count.sh $my_args
echo "Count of arguments when using direct string:"
./arguments_count.sh 1 2 3 '4 5' 6

Output after execute test.sh is:

Code:

Count of arguments when using my_args:
Number of arguments=6
Count of arguments when using direct string:
Number of arguments=5

What should I do to get output for "my_args" the same as for direct string?

Did you try double quoting $my_args?

Yes and the result is "1 argument".

Yes I see; just found out myself. hmmm - I don't seem to achieve the desired result playing around... sorry.

I wonder if not because comparing a variable with many values...What about comparing the same ?:

Code:

./arguments_count.sh $(echo 1 2 3 '4 5' 6)

The problem is in the field splitting, after expansion of variable my_args. It is split into 6 fields:
1 2 3 '4 5' and 6
You see you called it my_args, but you turned it into a string instead of discrete arguments. By unquoting the string expansion you are not getting the arguments back, but 6 fields that stem from that string split on white space...

An alternative would be to use positional parameters:

Code:

set -- 1 2 3 '4 5' 6
echo "Count of arguments when using positional parameters"
./arguments_count.sh "$@"

--
If you are using bash, ksh93 or zsh you could try arrays:

Code:

my_args=(1 2 3 '4 5' 6)
echo "Count of arguments when using my_args array:"
./arguments_count.sh "${my_args[@]}"

Code:

Count of arguments when using positional parameters
Number of arguments=5
Count of arguments when using my_args array:
Number of arguments=5

Code:

echo "$4"; echo "${my_args[3]}"
4 5
4 5

Scrutinizer is - as always - correct, but i suppose the problem comes from not understanding the quotation process:

The shell maintains a SINGLE flag for being inside a single- or double-quoted string. That means, that quotes can - unlike brackets - in no way be nested!

Consider:

Code:

(abc(def)ghi)
"abc"def"ghi"

These are completely different: there is not a string "def", which is part of a larger string "abc"def"ghi" (like the brackets-expression might be) but a string "abc", another string "ghi" and some unquoted "def" in between these two. So far so obvious and generally known.

But when it comes to single-quoted strings inside double-quoted strings some people think these are somehow nested:

Code:

"abc'def'ghi"

But this is not the case at all! In fact a single-quote character loses it special power to start or end a quotation inside a double.quoted string (and vice versa). That is, in the above example, the character between "c" and "d" is just an ordinary character, like "x" or any other.

If you want to create "nested quotes", which "peel off" one layer after the other you have to use escapes:

Code:

$ my_args="a b c \'d e\' f g"
$ arguments_count.sh $my_args

I hope this helps.

bakunin


I hope this helps.

bakunin