shell programming - how to properly pass variables within a function

Question

What's wrong with my bash script? I'm trying to pass positional parameters within a function. My last test - Test 4 works but its basically the command that I would run on the command line, no variable substitution.

I would like to call my function. Can someone tell me if the construction of my first 3 tests are valid and how to I can correct them? Thanks!

To execute: ./myscript.sh dev01 tester

#!/bin/bash

set +x

if [[ $# != 2 ]]; then
   echo "Usage: ./script.sh <ENV> <COMPONENT>"
   exit 1
fi

# Setup VARS
CREDS="-x foobar -a ec2.local_ipv4"
ENVIRONMENT="$1"
ROLES="$2"

function deploy {
    knife ssh "$CREDS" "chef_environment:"$ENVIRONMENT" AND roles:*"$ROLES"*" "uname"
}

echo "Test 1"
deploy

echo "Test 2"
DEPLOY=$(knife ssh "$CREDS" "chef_environment:"${ENVIRONMENT}" AND roles:*"${ROLES}"*" "uname")
$DEPLOY

echo "Test 3"
knife ssh "$CREDS" "chef_environment:"$ENVIRONMENT" AND roles:*"$ROLES"*" "uname"

echo "Test 4"
knife ssh -x foobar -a ec2.local_ipv4 "chef_environment:dev01 AND roles:*tester*" "uname"

Again, Test 4 works only.

Consider making a habit of using deploy() { instead of function deploy { -- the former syntax works in any POSIX-compliant shell, whereas the latter depends on extensions and has no benefit to compensate for that lack of portability. And consider mklement0's note about all-uppercase variable names being in reserved space echoed. — Charles Duffy
– Charles Duffy, Commented Oct 29, 2016 at 4:03
...back towards the topic of the immediate problem, btw, you might consider BashFAQ #50 additional reading (above and beyond the applicable, useful, and correct references given in said answer). — Charles Duffy
– Charles Duffy, Commented Oct 29, 2016 at 4:06

mklement0 · Accepted Answer · 2016-10-29 04:03:01Z

2

Your problem is unrelated to using a function; it has to do with how you're storing arguments in a variable and using that variable later:

If you want to store multiple arguments in a (non-array) variable, you cannot reference that variable double-quoted, because the value is then passed as a single argument to the target utility.

An immediate fix would be to use $CREDS unquoted, but that makes the value subject to potentially unwanted shell expansions, so the robust way to pass multiple arguments is to use an array:

# Store args. individually as array elements
CREDS=( '-x' 'foobar' '-a' 'ec2.local_ipv4' )

# ...

# "${CREDS[@]}" passes the elements of the array safely as *individual*
# arguments.
knife ssh "${CREDS[@]}" "chef_environment:$ENVIRONMENT AND roles:*$ROLES*" "uname"

Also note how I've embedded the $ENVIRONMENT and $ROLES variable references directly in the double-quoted string, which also makes the command more robust.

Finally, it's better not to use all-uppercase shell-variable names in order to avoid conflicts with environment variables and special shell variables.

edited Oct 29, 2016 at 4:03

answered Oct 29, 2016 at 3:57

mklement0

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1 Comment

noober Over a year ago

Awesome! Thanks for your clarity and detailed explanations! I appreciate the help.

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