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[ Next Article | Previous Article | Book Contents | Library Home | Legal | Search ] \r\n--------------------------------------------------------------------------------\r\nCommands Reference, Volume 2 \r\n\r\n--------------------------------------------------------------------------------\r\n\r\nfc Command\r\nPurpose\r\nProcesses the command history list.\r\n\r\nSyntax \r\nTo Open an Editor to Modify and Reexecute Previously Entered Commands\r\nfc [ -r ] [ -e Editor ] [ First [ Last ] ]\r\n\r\nTo Generate a Listing of Previously Entered Commands\r\nfc -l [ -n ] [ -r ] [ First [ Last ] ]\r\n\r\nTo Reexecute a Previously Entered Command\r\nfc -s [ Old=New ] [ First ]\r\n\r\nDescription\r\nThe fc command displays the contents of your command history file or invokes an editor to modify and reexecutes commands previously entered in the shell.\r\n\r\nThe command history file lists commands by number. The first number in the list is selected arbitrarily. The relationship of a number to its command does not change except when the user logs in and no other process is accessing the list. In that case, the system resets the numbering to start the oldest retained command at 1. \r\n\r\nIf the numbers in the command history file reach a limit greater than the value of the HISTSIZE environment variable or 32767, whichever is greater, the shell wraps to 1. Despite this optional number wrapping, the fc command maintains the time-ordering sequence of the commands. For example, if three commands in sequence are given the numbers 32766, 32767, and 1 (wrapped), command 32767 is still considered previous to command 1.\r\n\r\nThe commands in the history file can be displayed using the -l (lowercase L) flag. When the -l flag is not specified and commands are edited using the -e Editor flag, the resulting lines are entered at the end of the history file and then reexecuted by the shell (the fc -e Editor command is not entered into the command history list). If the editor returns a non-zero exit status, this suppresses entry in the history file and command reexecution.\r\n\r\nAny command-line variable assignments or redirection operators used with the fc command again invoke the previous command, suppressing standard error for both the fc command and the previous command. For example:\r\n\r\nfc -s -- -1 2>/dev/null\r\nFlags\r\n-e Editor Edits commands using the specified editor. The Editor parameter should be a command name. The command is located using the PATH environment variable. The value in the FCEDIT environment variable is used as a default when the -e flag is not specified. If the FCEDIT environment variable is null or unset, the ed editor is used. \r\n-l (lowercase L) Lists the commands in your history file. No editor is invoked to modify them. The commands are written in the sequence indicated by the First and Last parameters, as affected by the -r flag, with each command preceded by the command number. \r\n-n Suppresses command numbers when used with the -l flag. \r\n-r Reverses the order of the commands listed (when used with the -l flag) or reverses the order of the commands edited (when the -l flag is not specified). \r\n-s Reexecutes a command without invoking an editor. If the First parameter is not also specified, the -s flag reexecutes the previous command. \r\n\r\nParameters\r\nFirst or Last Selects the commands to list or edit. The number of previous commands that can be accessed is determined by the value of the HISTSIZE environment variable. The First and Last parameters must have one of the following values: [+] Number Represents a specific command number. Command numbers can be displayed with the -l flag. A + (plus sign) is the default. \r\n-Number Represents a command that was previously executed, specified by the number of commands to back up in the history list. For example, -1 indicates the immediately previous command. \r\nString Indicates the most recently entered command that begins with the specified string. If the Old=New parameter is specified without the -s flag, the string from the First parameter cannot contain an embedded = (equal sign). \r\n\r\nWhen using the -s flag, omission of the First parameter causes the previous command to be used.\r\n \r\n\r\nWhen the -s flag is not specified, the following rules apply:\r\n\r\nWhen using the -l flag, omission of the Last parameter causes a default to the previous command. \r\nWhen using the -r, -n, and -e flags, omission of the Last parameter causes a default to the First parameter. \r\nIf both the First and Last parameters are omitted, the previous 16 commands are listed or the previous single command is edited (depending on whether or not the -l flag is used). \r\nIf both the First and Last parameters are present, all commands are listed (when the -l flag is specified ) or edited (when the -l flag is not specified). Editing multiple commands is accomplished by presenting to the editor all the commands at one time, each command starting on a new line. If the First parameter represents a newer command than the Last parameter, the commands are listed or edited in reverse sequence. This is equivalent to using the -r flag. For example, the following commands on the first line are equivalent to the corresponding commands on the second line: \r\nfc -r 10 20 fc 30 40\r\nfc 20 10 fc -r 40 30\r\nWhen a range of commands is used, it is not an error to specify First or Last values that are not in the history list. The fc command substitutes the value representing the oldest or newest command in the list, as appropriate. For example, if there are only ten commands in the history list, numbered 1 to 10, the commands: \r\nfc -l\r\nfc 1 99\r\nlist and edit, respectively, all ten commands.\r\nOld=New In commands to be reexecuted, replaces the fist occurrence of the old string with the new string. \r\n\r\nEnvironment Variables\r\n\r\nThe following environment variables affect the execution of the fc command:\r\n\r\nFCEDIT When expanded by the shell, determines the default value for the -e editor variable. If the FCEDIT environment variable is null or is not set, the ed editor is the default. \r\nHISTFILE Determines the path name of the command history file. If the HISTFILE environment variable is not set, the shell may attempt to access or create the .sh_history file in the user\'s home directory. \r\nHISTSIZE Determines a decimal number representing the limit to the number of previous commands that are accessible. If this variable is not set, a default value of128 is used. \r\n\r\nExit Status\r\nThe following exit values are returned:\r\n\r\n0 Successful completion of the listing. \r\n>0 An error occurred. \r\n\r\nOtherwise, the exit status is that of the commands executed by the fc command.\r\n\r\nExamples\r\nTo invoke the editor defined by the FCEDIT environment variable on the most recent command (the default editor is /usr/bin/ed), enter: \r\nfc\r\nThe command is executed when you finish editing. \r\nTo list the previous two commands that were executed, enter: \r\nfc -l -2\r\nTo find the command that starts with cc, change foo to bar, and display and execute the command, enter: \r\nfc -s foo=bar cc\r\nFiles\r\n/usr/bin/ksh Contains the Korn shell fc built-in command. \r\n/usr/bin/fc Contains the fc command. \r\n\r\nRelated Information\r\nThe ksh command.\r\n\r\n\r\n--------------------------------------------------------------------------------\r\n\r\n[ Next Article | Previous Article | Book Contents | Library Home | Legal | Search ] |
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发表于 2002-03-14 05:18
发表于 2002-03-14 22:28
\r\n\r\nif you are paranoid, do something like this:\r\n\r\nrm .sh_history\r\nln -s /dev/null .sh_history
