| If a command is executed, and then a command with the same name is installed in a directory in the search path before the directory where the original command was found, the shell will continue to exec the original command. Use the -t option of the alias command to correct this situation. Some very old shell scripts contain a ^ as a synonym for the pipe character |. Using the hist built-in command within a compound command will cause the whole command to disappear from the history file. The built-in command . file reads the whole file before any commands are executed. Therefore, alias and unalias commands in the file will not apply to any commands defined in the file. Traps are not processed while a job is waiting for a foreground process. Thus, a trap on CHLD won't be executed until the foreground job terminates. It is a good idea to leave a space after the comma operator in arithmetic expressions to prevent the comma from being interpreted as the decimal point character in certain locales. | 
