Remove characters from string when passing as parameter

Question

I've tried Googling this and tested every permutation I could come up with, but I'm just not getting it. :(

I have a function which accepts an identified input string:

[user@Dreadnaught /]$ myfunction -w InputString

The function has several input options, so I need to identify that I'm passing my string to the -w option. The string I'm getting from another program has dashes in it:

In-put-St-ring

I can remove those dashes when testing an echo:

[user@Dreadnaught /]$ echo "In-put-St-ring" |tr -d -
InputString

But I can't figure out how to strip the dashes when passing to the function. I've tried (unsuccessfully):

[user@Dreadnaught /]$ OldString="In-put-St-ring"
[user@Dreadnaught /]$ echo $OldString
In-put-St-ring
[user@Dreadnaught /]$ NewString=$OldString|tr -d -
[user@Dreadnaught /]$ echo $NewString

[user@Dreadnaught /]$ NewString=$($OldString|tr -d -)
-ash: In-put-St-ring: not found
[user@Dreadnaught /]$ NewString=$("$OldString"|tr -d -)
-ash: In-put-St-ring: not found
[user@Dreadnaught /]$ NewString=$(""$OldString"|tr -d -")
-ash: In-put-St-ring|tr -d -: not found

and...

[user@Dreadnaught /]$ myfunction -w $("In-put-St-ring" |tr -d -)
-ash: In-put-St-ring: not found
myfunction: option requires an argument -- 'w'

and... a few more.

I'm sure it's simple for someone with more bash experience than me, but I'm stumped. Thanks for your help!

Answer 1

You forgot to use echo.

A pipe doesn't send variables to a command – a pipe connects one command's output to the other command's input. That is, the whole echo "In-put-St-ring" is first processed and only then its output is sent to tr; not the other way around.

In other words, every time a pipe is used, you can interpret it like this:

(echo "$OldString") | (tr -d -)

Because the syntax used inside $( ... ) substitution is exactly the same as in the "main" command line, you also need to use echo to actually produce the variable's contents as output before they can be piped:

NewString=$(echo "$OldString" | tr -d -)

myfunction -w "$(echo "$OldString" | tr -d -)"

That said, there is actually an alternative bash-specific method to pipe just some text without a whole command (although it's not necessarily better; in some cases perhaps even worse):

NewString=$(tr -d - <<< "$OldString")

myfunction -w "$(tr -d - <<< "$OldString")"

But instead of either, you should just use parameter expansion:

NewString=${OldString//-}

myfunction -w "${OldString//-}"