A substring is a adjacent sequence of characters within a string. In Bash, you can check if a string contains a substring using grep command and comparison methods.

Concatenation of strings is the most common process when working with string. In Bash, you can concatenate string variables using the concatenation operator + or by simply putting them next to each other.

You can check if a program exists from a Bash script using the command, type command or whish Is command followed by the name of the program you want to check.

You can use the "mkdir" command with the "-p" flag to create a directory only if it does not already exist. The "-p" flag creates any necessary parent directories if they do not exist.

In Bash, you can check if a file exists using the test command or the equivalent [ command. The most common way to check if a file does not exist is by using the -e option, which tests whether a file exists. To check if a file does not exist, you can negate this option using !

In Bash, you can use the IFS (Internal Field Separator) variable to specify the delimiter and the read command to split a string into tokens based on that delimiter.

You can obtain the directory where a Bash script is located from within the script itself by using the $0 parameter, which contains the path to the script that is currently running, and the dirname command, which extracts the directory portion of the path.