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I am trying to substitute a variable inside another variable in shell script. but its showing as empty string. Below is the scenario.

  1. Assigning "x" with string containing variable "abc"
~$ x="new value is \${abc}"
~$ echo $x
new value is ${abc}
  1. Below is content of script abc.sh, defining the value of abc->
#!/bin/bash
abc="something='123:234'"
xyz=$@
echo $xyz
  1. When executing command "sh abc.sh $x" getting below value.

actual -> new value is ${abc}

expected - > new value is something='123:234'

Please help solving above issue.

Thanks

1 Answer 1

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As you insert the value new value is ${abc}, the ${abc} part is just a string of characters. This string is not reevaluated for expansions when you do xyz=$@.

To expand ${abc} in the string, do the following in the script:

abc="something='123:234'"

eval "xyz=\"$1\""

printf '%s\n' "$xyz"

The eval takes a piece of shell code. The given code does xyz="$1", but with $1 replaced by the command line argument (the string new value is ${abc}). This statement is then reevaluated by the shell, assigning the correct string to the variable.

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  • Thanks for quick response @Kusalananda. Is there any other way where I dont need to edit the script and with some changes in variable "x" itself, results can be achieved.
    – RDP
    Oct 24, 2019 at 15:50
  • @RDP No, there is not.
    – Kusalananda
    Oct 24, 2019 at 15:51

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