AIX fc Command

逃离我推掉我的手 2023-10-05 09:49 10阅读 0赞

### Purpose ###

Processes the command history list.

### Syntax ###

**To Open an Editor to Modify and Reexecute Previously Entered Commands**

**fc** \[ [**-r**][-r] \] \[ [**-e**][-e] *Editor* \] \[ [*First*][First] \[ [*Last*][First] \] \]

**To Generate a Listing of Previously Entered Commands**

**fc** [**-l**][-l] \[ [**-n** ][-n_]\] \[ **-r** \] \[ *First* \[ *Last* \] \]

**To Generate a Listing of Previously Entered Commands with Time of Execution**

**fc** [**-t**][-t] \[ [**-n** ][-n_]\] \[ [**-r**][-r] \] \[ *First* \[ *Last* \] \]

**To Re-execute a Previously Entered Command**

**fc** [**-s**][-s] \[ [*Old*][Old]**=** [*New*][Old] \] \[ *First* \]

### Description ###

The **fc** command displays the contents of your command history file or invokes an editor to modify and reexecutes commands previously entered in the shell.

The 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.

If the numbers in the command history file reach a limit greater than the value of the [**HISTSIZE**][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.

The 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.

Any 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:

fc -s -- -1 2>/dev/null

### Flags ###

<table> 
 <thead> 
  <tr> 
   <th>Item</th> 
   <th>Description</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td><strong>-e</strong><em>&nbsp;Editor</em></td> 
   <td>Edits commands using the specified editor. The&nbsp;<em>Editor</em>&nbsp;parameter should be a command name. The command is located using the&nbsp;<strong>PATH</strong>&nbsp;environment variable. The value in the&nbsp;<strong>FCEDIT</strong>&nbsp;environment variable is used as a default when the&nbsp;<strong>-e</strong>&nbsp;flag is not specified. If the&nbsp;<strong>FCEDIT</strong>&nbsp;environment variable is null or unset, the ed editor is used.</td> 
  </tr> 
  <tr> 
   <td><strong>-l</strong></td> 
   <td>(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&nbsp;<em>First</em>&nbsp;and<em>&nbsp;Last</em>&nbsp;parameters, as affected by the&nbsp;<strong>-r</strong>&nbsp;flag, with each command preceded by the command number.</td> 
  </tr> 
  <tr> 
   <td><strong>-n</strong></td> 
   <td>Suppresses command numbers when used with the&nbsp;<strong>-l</strong>&nbsp;flag.</td> 
  </tr> 
  <tr> 
   <td><strong>-r</strong></td> 
   <td>Reverses the order of the commands listed (when used with the&nbsp;<strong>-l</strong>&nbsp;flag) or reverses the order of the commands edited (when the&nbsp;<strong>-l</strong>&nbsp;flag is not specified).</td> 
  </tr> 
  <tr> 
   <td><strong>-s</strong></td> 
   <td>Reexecutes a command without invoking an editor. If the&nbsp;<em>First</em>&nbsp;parameter is not also specified, the&nbsp;<strong>-s</strong>&nbsp;flag re-executes the previous command.</td> 
  </tr> 
  <tr> 
   <td><strong>-t</strong></td> 
   <td>Lists the commands in your history file along with there time of execution. The working is similar to&nbsp;<strong>-l</strong>&nbsp;flag but the time of execution of the command is displayed. <p>NoteIf the time field is recorded previously by setting&nbsp;<code>EXTENDED_HISTORY=ON</code>, then formatted time field is displayed, else "?".</p> </td> 
  </tr> 
 </tbody> 
</table>

### Parameters ###

<table> 
 <thead> 
  <tr> 
   <th>Item</th> 
   <th>Description</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td><em>First</em>&nbsp;or<em>&nbsp;Last</em></td> 
   <td>Selects the commands to list or edit. The number of previous commands that can be accessed is determined by the value of the&nbsp;<strong>HISTSIZE</strong>&nbsp;environment variable. The&nbsp;<em>First</em>&nbsp;and&nbsp;<em>Last</em>&nbsp;parameters must have one of the following values: <p>[<strong>+</strong>]&nbsp;<em>Number</em></p> <p>Represents a specific command number. Command numbers can be displayed with the&nbsp;<strong>-l</strong>&nbsp;flag. A + (plus sign) is the default.</p> <p><strong>-</strong><em>Number</em></p> <p>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.</p> <p><em>String</em></p> <p>Indicates the most recently entered command that begins with the specified string. If the&nbsp;<em>Old</em><strong>=</strong><em>New</em>&nbsp;parameter is specified without the&nbsp;<strong>-s</strong>&nbsp;flag, the string from the&nbsp;<em>First</em>&nbsp;parameter cannot contain an embedded&nbsp;<strong>=</strong>&nbsp;(equal sign).</p> <p>When using the&nbsp;<strong>-s</strong>&nbsp;flag, omission of the&nbsp;<em>First</em>&nbsp;parameter causes the previous command to be used.</p> </td> 
  </tr> 
 </tbody> 
</table>

When the **-s** flag is not specified, the following rules apply:

*  When using the **-l** flag, omission of the *Last* parameter causes a default to the previous command.
 *  When using the **-r**, **-n**, and **-e** flags, omission of the *Last* parameter causes a default to the *First* parameter.
 *  If 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).
 *  If 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:
    
        fc  -r  10  20           fc      30  40
        fc      20  10           fc  -r  40  30
 *  When 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:
    
        fc  -l
        fc   1   99
    
    list and edit, respectively, all ten commands.

<table> 
 <thead> 
  <tr> 
   <th>Item</th> 
   <th>Description</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td><em>Old</em><strong>=</strong><em>New</em></td> 
   <td>In commands to be reexecuted, replaces the fist occurrence of the old string with the new string.</td> 
  </tr> 
 </tbody> 
</table>

### Environment Variables ###

The following environment variables affect the execution of the **fc** command:

<table> 
 <thead> 
  <tr> 
   <th>Item</th> 
   <th>Description</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td><strong>EXTENDED_HISTORY</strong></td> 
   <td>Used to control the recording of time of command execution in the history file. If the variable is set to&nbsp;<code>ON</code>&nbsp;then the time is recorded, otherwise, it is not recorded.</td> 
  </tr> 
  <tr> 
   <td><strong>FCEDIT</strong></td> 
   <td>When expanded by the shell, determines the default value for the&nbsp;<strong>-e</strong><em>&nbsp;editor</em>&nbsp;variable. If the&nbsp;<strong>FCEDIT</strong>&nbsp;environment variable is null or is not set, the ed editor is the default.</td> 
  </tr> 
  <tr> 
   <td><strong>HISTDATEFMT</strong></td> 
   <td>This is used to control the format of the time displayed by the&nbsp;<strong>fc –t</strong>&nbsp;command. For example, if&nbsp;<code>HISTDATEFMT=%Y</code>, then&nbsp;<strong>fc -t</strong>&nbsp;will display the year when the command is executed. The formatting is similar to that done by&nbsp;<strong>date</strong>&nbsp;command.</td> 
  </tr> 
  <tr> 
   <td><strong>HISTFILE</strong></td> 
   <td>Determines the path name of the command history file. If the&nbsp;<strong>HISTFILE</strong>&nbsp;environment variable is not set, the shell may attempt to access or create the&nbsp;<strong>.sh_history</strong>&nbsp;file in the user's home directory.</td> 
  </tr> 
  <tr> 
   <td><strong>HISTSIZE</strong></td> 
   <td>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.</td> 
  </tr> 
 </tbody> 
</table>

### Exit Status ###

The following exit values are returned:

<table> 
 <thead> 
  <tr> 
   <th>Item</th> 
   <th>Description</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td><strong>0</strong></td> 
   <td>Successful completion of the listing.</td> 
  </tr> 
  <tr> 
   <td><strong>&gt;0</strong></td> 
   <td>An error occurred.</td> 
  </tr> 
 </tbody> 
</table>

Otherwise, the exit status is that of the commands executed by the **fc** command.

### Examples ###

1.  To invoke the editor defined by the **FCEDIT** environment variable on the most recent command (the default editor is **/usr/bin/ed**), enter:
    
        fc
    
    The command is executed when you finish editing.
2.  To list the previous two commands that were executed, enter:
    
        fc -l -2
3.  To find the command that starts with cc, change foo to bar, and display and execute the command, enter:
    
        fc -s foo=bar cc
4.  To list the previously executed commands along with there time of execution, type:
    
        fc –t

### Files ###

<table> 
 <thead> 
  <tr> 
   <th>Item</th> 
   <th>Description</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td><strong>/usr/bin/ksh</strong></td> 
   <td>Contains the Korn shell&nbsp;<strong>fc</strong>&nbsp;built-in command.</td> 
  </tr> 
  <tr> 
   <td><strong>/usr/bin/fc</strong></td> 
   <td>Contains the&nbsp;<strong>fc</strong>&nbsp;command.</td> 
  </tr> 
 </tbody> 
</table>

[-r]: https://www.ibm.com/support/knowledgecenter/ssw_aix_72/f_commands/fc.html?view=kc#fc__row-d3e98127
[-e]: https://www.ibm.com/support/knowledgecenter/ssw_aix_72/f_commands/fc.html?view=kc#fc__row-d3e98080
[First]: https://www.ibm.com/support/knowledgecenter/ssw_aix_72/f_commands/fc.html?view=kc#fc__row-d3e98178
[-l]: https://www.ibm.com/support/knowledgecenter/ssw_aix_72/f_commands/fc.html?view=kc#fc__row-d3e98103
[-n_]: https://www.ibm.com/support/knowledgecenter/ssw_aix_72/f_commands/fc.html?view=kc#fc__row-d3e98118
[-t]: https://www.ibm.com/support/knowledgecenter/ssw_aix_72/f_commands/fc.html?view=kc#fc__row-d3e98151
[-s]: https://www.ibm.com/support/knowledgecenter/ssw_aix_72/f_commands/fc.html?view=kc#fc__row-d3e98139
[Old]: https://www.ibm.com/support/knowledgecenter/ssw_aix_72/f_commands/fc.html?view=kc#fc__row-d3e98343
[HISTSIZE]: https://www.ibm.com/support/knowledgecenter/ssw_aix_72/f_commands/fc.html?view=kc#fc__row-d3e98422