replace characters in Zsh variable

Question

I am trying to replace all the - chars with _ chars in a specific variable. Tried to use the tr function. What am I missing?

Thanks!

user@mbp-user ~ % echo $APP_ID
app1_someinfo_info-text_text-indfo_text
user@mbp-user ~ % APP_ID= $APP_ID tr - _
zsh: command not found: app1_someinfo_info-text_text-indfo_text
user@mbp-user ~ % APP_ID= $APP_ID tr "-" "_"
zsh: command not found: app1_someinfo_info-text_text-indfo_text
user@mbp-user ~ % 

Answer 1

You can do this without invoking any other processes.

$ APP_ID=app1_someinfo_info-text_text-indfo_text
$ echo $APP_ID
app1_someinfo_info-text_text-indfo_text
$ echo ${APP_ID//-/_}
app1_someinfo_info_text_text_indfo_text

Or reassign to the same variable

$ APP_ID=${APP_ID//-/_}

Specifically we are using the pattern

name//pattern/string

which replaces all occurrences of pattern with string in the variable name.

Answer 2

Try the following:

[user@host ~]$ APP_ID="app1_someinfo_info-text_text-indfo_text"
[user@host ~]$ APP_ID=$(echo $APP_ID | tr "-" "_")
[user@host ~]$ echo $APP_ID
app1_someinfo_info_text_text_indfo_text