expr:tldr:30178

The command expr index "${string}" "${chars}" is used to find the index (position) of the first occurrence of any character in the chars string within the string string. Here's how it works:

1. ${string} is a variable representing the string in which you want to search for a character.
2. ${chars} is a variable representing the characters you are searching for within the string.
3. The expr index command is used to search for the first occurrence of any character from ${chars} within ${string}.
4. If a character from ${chars} is found in ${string}, the command returns the index (position) of the first occurrence. The first character in ${string} has an index of 1.
5. If none of the characters from ${chars} are found within ${string}, the command returns 0.
6. The result of this command is often used in shell scripts or command line operations to determine the index of a specific character within a string.

For example, if you have string="Hello, World!" and chars="Wo", the expr index "${string}" "${chars}" command will return 8 because the first occurrence of either 'W' or 'o' in the string is at index 8.