fc

The command history list shall reference commands by number. The first number in the list is selected arbitrarily. The relationship of a number to its command shall not change except when the user logs in and no other process is accessing the list, at which time the system may reset the numbering to start the oldest retained command at another number (usually 1). When the number reaches an implementation-defined upper limit, which shall be no smaller than the value in HISTSIZE or 32767 (whichever is greater), the shell may wrap the numbers, starting the next command with a lower number (usually 1). However, despite this optional wrapping of numbers, fc shall maintain the time-ordering sequence of the commands. For example, if four commands in sequence are given the numbers 32766, 32767, 1 (wrapped), and 2 as they are executed, command 32767 is considered the command previous to 1, even though its number is higher. When commands are edited (when the -l option is not specified), the resulting lines shall be entered at the end of the history list and then re-executed by sh . The fc command that caused the editing shall not be entered into the history list. If the editor returns a non-zero exit status, this shall suppress the entry into the history list and the command re-execution. Any command line variable assignments or redirection operators used with fc shall affect both the fc command itself as well as the command that results; for example: reinvokes the previous command, suppressing standard error for both fc and the previous command. (The letter ell.) List the commands rather than invoking an editor on them. The commands shall be written in the sequence indicated by the first and last operands, as affected by -r , with each command preceded by the command number. A positive number representing a command number; command numbers can be displayed with the -l option. number A negative decimal number representing the command that was executed number of commands previously. For example, -1 is the immediately previous command. A string indicating the most recently entered command that begins with that string. If the old = new operand is not also specified with -s , the string form of the first operand cannot contain an embedded . This variable, when expanded by the shell, shall determine the default value for the -e editor option's editor option-argument. If FCEDIT is null or unset, ed shall be used as the editor. Determine a pathname naming a command history file. If the HISTFILE variable is not set, the shell may attempt to access or create a file .sh history in the directory referred to by the HOME environment variable. If the shell cannot obtain both read and write access to, or create, the history file, it shall use an unspecified mechanism that allows the history to operate properly. (References to history "file" in this section shall be understood to mean this unspecified mechanism in such cases.) An implementation may choose to access this variable only when initializing the history file; this initialization shall occur when fc or sh first attempt to retrieve entries from, or add entries to, the file, as the result of commands issued by the user, the file named by the ENV variable, or implementation-defined system start-up files. In some historical shells, the history file is initialized just after the ENV file has been processed. Therefore, it is implementation-defined whether changes made to HISTFILE after the history file has been initialized are effective. Implementations may choose to disable the history list mechanism for users with appropriate privileges who do not set HISTFILE ; the specific circumstances under which this occurs are implementation-defined. If more than one instance of the shell is using the same history file, it is unspecified how updates to the history file from those shells interact. As entries are deleted from the history file, they shall be deleted oldest first. It is unspecified when h