Other Ways to Access Your History

Other Ways to Access Your History There are several other ways to access your command history that are worth noting. The history Command The operation of the history command differs between the Korn shell and Bash because it is not part of the POSIX standard. The Korn shell history command writes your last 16 commands to standard output: $ history 507 cd shell 508 cd ch15 509 vi int 510 ps 511 echo $HISTSIZE 512 cat $ENV 513 cp int int.sv 514 history 515 exit 516 cd shell 517 cd ch16 518 vi all 519 run -n5 all 520 ps 521 lpr all.out 522 history The numbers to the left are simply relative command numbers (command number 1 would be the first, or oldest, command in your history). Without any arguments, the Bash history command lists your entire history (as specified by the HISTSIZE variable) to standard output. If you just want to see the last few commands, you must specify the number of commands to display as an argument: $ history 10 513 cp int int.sv 514 history 515 exit 516 cd shell 517 cd ch16 518 vi all 519 run -n5 all 520 ps 521 lpr all.out 522 history 10 $ The fc Command The fc command allows you to start up an editor on one or more commands from your history or to simply write a list of history commands to your terminal. In the latter form, which is indicated by giving the -l option to fc, it is like typing in history, only more flexible (you can specify a range of commands to be listed or can get fewer or more than the last 16 commands listed). For example, the command fc -l 510 515 writes commands 510 through 515 to standard output, whereas the command fc -n -l -20 writes the last 20 commands to standard output, not preceded by line numbers (-n). Suppose that you've just executed a long command line and then decide that it would be nice to turn that command line into a shell program called runx. You can use fc to get the command from your history and I/O redirection to write that command to a file: fc -n -l -1 > runx (That's the letter l followed by the number -1.) fc is described in full detail in Appendix A. The r Command A simple Korn shell command allows you to re-execute previous commands using even a fewer number of keystrokes than described. If you simply type in the r command, the Korn shell re-executes your last command: $ date Thu Oct 24 14:24:48 EST 2002 $ r Re-execute previous command date Thu Oct 24 14:25:13 EST 2002 $ When you type in the r command, the Korn shell redisplays the previous command and then immediately executes it. If you give the r command the name of a command as an argument, the Korn shell re-executes the most recent command line from your history that begins with the specified argument: $ cat docs/planA ... $ pwd /users/steve $ r cat Rerun last cat command cat docs/planA $ Once again, the Korn shell redisplays the command line from its history before automatically re-executing it. The final form of the r command allows you to substitute the first occurrence of one string with the next. To re-execute the last cat command on the file planB instead of planA, you could type: $ r cat planA=planB cat docs/planB ... $ or even more simply, you could have typed: $ r cat A=B cat docs/planB ... $ Bash has the ! built-in command; !! re-executes the previous command, and !string re-executes the most recent command line from your history that begins with string: $ !! cat docs/planB ... $ !d date Thu Oct 24 14:39:40 EST 2002 $ Note that no spaces can exist between ! and string. The fc command can be used with the �s option to do the same thing with any POSIX-compliant shell (the r command is actually an alias to the fc command in the Korn shell�more on that later in this chapter): $ fc �s cat cat docs/planB ... $ fc �s B=C cat docs/planC ... $