Bash for loop not understanding variables correctly?

Question

How can I increment a variable already defined in bash? Here's what I mean:

ID1="YAY1"
ID2="YAY2"
for (( c=1; c<=3; c++ ))
  do
    if [ "$SOMEOTHERVAR" = "ID$c" ]; then BLAH; fi
  done

Problem is, when it increments the variable already defined to do the comparison, it thinks ID$c is equal to the string ID1, not what ID1 equals which is YAY1, so the if statement always evaluates false. I hope that makes sense.

Thank you for your help!

******UPDATE******

Thanks everyone for your help. The cleanest solution was to use a single array mixed with cut. May not be the cleanest way, but works great. Here is a snippet below:

# CONTACTS
declare -a EMAIL
EMAIL[1]="JS:[email protected]"
EMAIL[2]="JD:[email protected]"
EMAIL[3]="JK:[email protected]"

# FUNCTIONS
function EMAIL {
  for i in "${!EMAIL[@]}"; do
    POINTER="`echo ${EMAIL[$i]} | cut -d":" -f1`"; ADDRESS="`echo ${EMAIL[$i]} | cut -d":" -f2`";
    if [ "$POINTER" = "$PEMAIL" ]; then TO="$ADDRESS"; fi
    if [ "$POINTER" = "$SEMAIL" ]; then CC="$ADDRESS"; fi
  done
}

PEMAIL and SEMAIL are the comparators which are pulled from the database in another part of the script.

Shad · Accepted Answer · 2013-04-12 00:03:50Z

2

Create an intermediate variable (which I called newVar) that builds the variable name. Then dereference that. The following code will print "match for index 2"

ID1="YAY1"
ID2="YAY2"
for (( c=1; c<=3; c++ ))
  do
    newVar="ID${c}"
    if [ "YAY2" = "${!newVar}" ]; then echo "match for index $c"; fi
  done

answered Apr 12, 2013 at 0:03

Shad

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1 Comment

Atomiklan Over a year ago

Thank you for the help. I played around with this idea, but unfortunately I couldn't relate the two variables the way they needed to be. See update in original post. Thank you!

kojiro · Accepted Answer · 2013-04-12 00:00:45Z

1

In your example it just makes sense to use an array, since the last part of the variable is an integer anyway:

declare -a ids
ids[1]="YAY1"
ids[2]="YAY2"
for (( c=1; c < 3; c++ )); do
    if [ "$SOMEOTHERVAR" = "${ids[c]}" ]; then
        BLAH
    fi
done

If it won't always be an integer, and you have bash 4, you can use an associative array:

declare -A ids
ids['glow']="YAY1"
ids['stix']="YAY2"
for c in glow stix; do
    if [ "$SOMEOTHERVAR" = "${ids[c]}" ]; then
        BLAH
    fi
done

answered Apr 12, 2013 at 0:00

kojiro

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5 Comments

Atomiklan Over a year ago

That a perfect solution which I would have liked to use but I thought bash couldn't handle arrays for some reason. Maybe its that it can't handle multidimensional arrays which is what I need for part two of this simplified example. Can you show me an example of this using a multidimensional array? I gave up long ago trying to use multidimensional arrays in bash but you have sparked my interest again. Thanks very much for the help.

Atomiklan Over a year ago

ie. Eventually I need to associate a another variable with "YAY1". A better real world example would be: JS:[email protected] Thank you for your help. As a side note, im not asking you to write this for me, just want to put into context what im trying to accomplish. Thank you! JD:[email protected] Here's the logic: if the following variable (example JD, pulled from another area of script) = the id in array (JD), then set CC field to [email protected]

Atomiklan Over a year ago

One last thought. I still dont think multidimensional arrays are possible in bash without "faking" it. Maybe the best way to do what im trying to do is with say a small database inside the script using colon or comma separated values. JD:[email protected] then just do a while loop with a grep and cut to pull out the info needed. All that im trying to accomplish it this: in a database, a user is "checkmarked" to be CC included in an email alert. When they are marked, they're name is tied to a 2 character variable JD, JR etc. When the script runs, it sees who to send the CC to based on the var.

Atomiklan Over a year ago

ie. In database Jane Doe is set to receive CC email therefore a field in the database is flagged as JD. When the script runs it compares that flag JD to an internal listing of admins and sends Jane Doe the email. I hope this is making sense...

Atomiklan Over a year ago

Excellent! Thank you kojiro, your solution ultimately pointed me in the right direction to a solution. I have posted a snippet of my code above (In the original post) so you can see what the final solution was.

Fritz G. Mehner · Accepted Answer · 2013-04-12 08:34:17Z

0

A solution without a C-style loop:

ID1="YAY1"
ID2="YAY2"

for name in ${!ID*}; do
  if [ "$SOMEOTHERVAR" == "${!name}" ]; then echo "match for $name"; fi
done

${!ID*} expands to the list of all variables with prefix 'ID'.

answered Apr 12, 2013 at 8:34

Fritz G. Mehner

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1 Comment

Atomiklan Over a year ago

Excellent, thank you for the help. Didn't get a chance to read your suggestion. Already found a solution. Thank you though!

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