Ubuntu – Echo script arguments from function

14.04bashscripts

I need to get script arguments within function with arguments.

./myscript 1 2 3

function_name () {
   if [ $1 == 3 ]; then
        # I need the $1 in the following echo to be the script argument, not the function argument
        echo $1 $2 $3
   fi
}

function_name $#

Best Answer

That's quite interesting. The problem is the scope of the function is overriding that of the script. I can't see a simple way around that.

However, you can just pass the variables along as arguments (into the function):

function_name () {
   [[ $# == 3 ]] && echo $1 $2 $3
}

function_name $@

Or you could:

Pass $# $@, check $1, and echo $2 $3 $4
Pass $# $@, check $1, shift and then echo $1 $2 $3
Store $@ as a script-level variable and access it from within the function

Related Solutions

Ubuntu – How to make the argument as optional in bash

If you won't pass arguments with spaces:

sum() {  
[[ -n $2 ]] && echo $(( $(tr ' ' '+' <<<"$@") ))
}

Effect:

$ sum 1 2 3
6

Explanation:

<<<"some string" feeds in only "some string" as the input. Think of it as shorthand for echo "some string" |. It is called a Here String.
"$@" expands into all the positional parameters, separated by spaces. It is equivalent to "$1 $2 ...".
Hence, tr ' ' '+' <<<"$@" outputs "$1+$2+$3...", which is evaluated by the outer $(( )).
[[ -n $2 ]] tests if the second parameter is non-empty. You could replace [[ -n $2 ]] && with [[ -z $2 ]] ||.

Another way:

sum() {
[[ -n $2 ]] && (IFS=+; echo $(( $* )))
}

Explanation:

$* is just like $@, except that the parameters are not separated by spaces, but by the first character of the Internal Field Separator (IFS). With IFS=+, it expands to "$1+$2+...". See What is the difference between $* and $@?
We set IFS in a subshell (note the surrounding parentheses) so that the main shell isn't affected. IFS is, by default: \t\n (space, tab, newline). This is an alternative to using local variables.

Now to answer your question:

You can use a default value for any variable or parameter. Either:

SUM() { 
 echo "The sum is $(($1+$2+${3:-0}+${4:-0}+${5:-0}+${6:-0}+${7:-0}+${8:-0}+${9:-0}))" || false
}

Or:

SUM() { 
 echo "The sum is $(($1+$2+${3:=0}+${4:=0}+${5:=0}+${6:=0}+${7:=0}+${8:=0}+${9:=0}))" || false
}

Ubuntu – Pass arguments from file line by line to function

Assuming your list of files is one filename per line, the xargs utility should be able to handle filenames with spaces in them if you specify newline as the delimiting character e.g.

xargs -d '\n' file < filelist.txt

If you prefer to use a shell function

while IFS= read -r f; do [[ -z "$f" ]] || file "$f"; done < filelist.txt

Best Answer

Related Solutions

Ubuntu – How to make the argument as optional in bash

Ubuntu – Pass arguments from file line by line to function

Related Question