How can I access an environment variable from another? I have the following in my shell
#!/usr/bin/env bash
set -x
export A_version=1.0.0
component=A
echo ${${component}_version}}
the bash script after the run gives me
temp.sh: line 9: ${${component}_version}}: bad substitution
You can use eval to do this. Here is a working version of your script that prints 1.0.0:
export A_version=1.0.0
component=A
eval "echo \$${component}_version"
For more information, see this page:
http://tldp.org/LDP/abs/html/ivr.html
Update: A safer way to do the same thing in Bash would be:
export A_version=1.0.0
component=A
var=${component}_version; echo "${!var}"
Note that you have to run this script with bash, not sh.
eval for indirect evaluation, or encourage the ABS as a reference -- it's very much the W3Schools of bash; half of what we do in the freenode #bash channel is help people unlearn bad habits they picked up there. BashFAQ #6 is a reference on indirect variable use that's more actively focused on best practices. The bash-hackers' wiki also covers indirection in its page on parameter expansion.
eval "echo \$${component}_version"? would that work?eval "echo \\$${component}_version"works.component='(rm -rf ~)', then you're in a very bad place when you run that. Other (non-eval-based) parameter expansion syntax doesn't carry those risks. See also BashFAQ #48 re: whyevalis generally discouraged.eval. How about you post an answer here with one?_versionto the variable name before accessing it, so this should be reponed.