BASH, passing multi-item variable to function

Question

I have a function:

function checkConn()
{
    RET=0
    echo "in function: ${2}"
    echo
    for i in `cat ${1}`
    do
        for p in ${2}
        do
            if nc -dzw 2 ${i} ${p}  2>&1 >/dev/null

and so on.

In the "main" body of the script, I have the following:

PORTS='22 161 162 1521'
checkConn ${FILE} ${PORTS}

FILE is the name of a file which contains a list of IPs.

When I pass PORTS to the function, only the 1st item gets passed. I also tried it with double-quotes.

I put that "echo" statement to confirm. It only shows the first item in PORTS, which is 22.

How can I pass all the ports to this function, and then loop through each one?

shellcheck.net is generally a good place to start, by the way -- you're missing a lot of quotes that are necessary to avoid being surprised by corner-case behavior when processing unusual data. See also Don't Read Lines With For — Charles Duffy
– Charles Duffy, Commented Apr 4, 2017 at 15:24
Also, don't use string variables to store lists. ports=( 22 161 162 1521 ) is the correct way to define an array named ports. checkConn "$file" "${ports[@]}" will pass the filename as the first argument and the individual ports as subsequent arguments; inside that function, one can do something like checkConn() { file=$1; shift; for port; do echo "Checking port "$port"; done; } -- iterating over the argument vector. — Charles Duffy
– Charles Duffy, Commented Apr 4, 2017 at 15:27
(And don't use all-caps variable names -- see pubs.opengroup.org/onlinepubs/9699919799/basedefs/…, defining all-caps names as for use for variables with meaning to the operating system or shell, and reserving names with lowercase characters for application use; since setting a shell variable overwrites any like-named environment variable, the naming conventions apply in both places). — Charles Duffy
– Charles Duffy, Commented Apr 4, 2017 at 15:29

Charles Duffy · Accepted Answer · 2017-04-04 15:42:20Z

Best practice is to pass the list of ports as individual arguments, each with their own argv entry -- like so:

checkConn() {
  file=$1; shift  ## read filename from $1, then remove it from the argument list

  while IFS= read -r address; do
    for port; do  ## we shifted off the filename so this only iterates over ports
      if nc -dzw 2 "$address" "$port" </dev/null >/dev/null 2>&1; then
        echo "$address $port OPEN"
      else
        echo "$address $port CLOSED"
      fi
    done
  done <"$file"
}

file=addrs.txt
ports=( 22 161 162 1521 )
checkConn "$file" "${ports[@]}"

Notes:

The function keyword is not actually required for use to define a function; it makes your code incompatible with POSIX sh, but provides no benefit over the portable syntax. Avoid it.
The while IFS= read -r idiom is described in detail in BashFAQ #1. Also see Don't Read Lines With For.
Arrays, as used in the ports=( ... ) and "${ports[@]}" syntax, are described in the BashGuide.

Inian · Accepted Answer · 2017-04-04 15:47:35Z

1

Multiple syntax violations and outdated constructs, you probably need something like,

function checkConn() {
    # define variables as local unless you are using it beyond the scope
    # of the function and always lower-case variable names 
    local ret=0
    printf "%s\n" "$2"

    # Splitting the string into an array so that it can be accessed 
    # element wise inside the loop. The -a option in read stores the  
    # elements read to the array
    read -ra portList <<<"$2"     

    # Input-redirection of reading the file represented by argument $1
    # representing the file name. The files are read one at a time    
    while IFS= read -r line; do
        # Array values iterated in a for-loop; do the action
        # for each value in the port number
        for port in "${portList[@]}"; do
            if nc -dzw 2 "$line" "$port"  2>&1 >/dev/null; then
                printf "%s %s\n" "$line" "$port"
                # Your rest of the code
            fi
        done
    done < "$1"
}

and call the function as

ports='22 161 162 1521'
filename="file"
checkConn "$filename" "$PORTS"

edited Apr 4, 2017 at 15:47

answered Apr 4, 2017 at 15:21

Inian

87.1k15 gold badges167 silver badges183 bronze badges

2 Comments

chepner Over a year ago

Your for loop is going to run exactly once, with port set to the value of portList.

Charles Duffy Over a year ago

It's a good answer. We differ only on some fairly minor points. :)

Collectives™ on Stack Overflow

BASH, passing multi-item variable to function

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related