macOS Mojave version 10.14.1 bash-3.2 expr: syntax error

问题

I meet such error:

expr: syntax error

and my script is:

#!/bin/bash
echo `expr index "sarasara"  a`

how to fix it.

回答1:

$ man expr gives this at the end:

According to the POSIX standard, the use of string arguments length, substr, index, or match produces undefined results. In this version of expr, these arguments are treated just as their respective string values.

In other words, macOS' expr does not support index.

来源：https://stackoverflow.com/questions/53701873/macos-mojave-version-10-14-1-bash-3-2-expr-syntax-error