Pattern: Use of undefined $'..'
Issue: -
You are using the interpolated string Bashism $'..' in a script that declares itself as POSIX sh (e.g. via #!/bin/sh).
To ensure the script runs correctly on other systems, either switch to Bash, or rewrite it in a POSIX compatible way.
This can generally done via printf as in the example. Be careful about strings with trailing linefeeds, as a $(command substitution) will strip them.
Example of incorrect code:
#!/bin/sh
IFS=$' \t\n'Example of correct code:
#!/bin/sh
# Note: \n can not be last, or it will be stripped by $()
IFS=$(printf ' \n\t')