c) History, Command Line Editing and Job Control
- Former user (Deleted)
History
The history command lists the last commands you typed.
-bash-4.1$ history
1 cd
2 ls -l
3 who
4 ps
5 sleep 200 &
6 ps
7 fg
8 history
-bash-4.1$
Command Line Editing
You can select past commands using the up and down arrow keys. You can edit the command line using the left and right arrow keys and any of the following commands:
| keystroke | result |
|---|---|
| Ctrl-P | previous command |
| Ctrl-N | next command |
| Ctrl-R string | previous command containing string |
| Ctrl-B | move back one character |
| Ctrl-F | move forward one character |
| DEL | delete previous character |
| Ctrl-D | delete character under cursor |
| ESC-D | delete word forward |
| ESC-H | delete word backward |
| Ctrl-T | transpose two characters |
| ESC-F | move forward one word |
| ESC-B | move back on word |
Job Control
Job control deals with managing your programs whilst they are running. Linux uses the name process for a running program. The ps command list all the processes you have running.
-bash-4.1$ ps PID TTY TIME CMD 14521 pts/3 00:00:00 bash 16165 pts/3 00:00:00 ps -bash-4.1$
From this we can see that we have two processes running, the bash shell and the ps command. Associated with each process is a unique identifier - PID (process ID).
We can manage processes, especially command that take a long time to run, by making them in the background process adding an '&' to the end of the line. The shell then becomes free for us to execute more commands.
-bash-4.1$ ps PID TTY TIME CMD 14521 pts/3 00:00:00 bash 17005 pts/3 00:00:00 ps -bash-4.1$ sleep 120 ^C -bash-4.1$ sleep 120 & [1] 17026 -bash-4.1$ ps PID TTY TIME CMD 14521 pts/3 00:00:00 bash 17026 pts/3 00:00:00 sleep 17027 pts/3 00:00:00 ps -bash-4.1$ echo I am doing other work I am doing other work -bash-4.1$ echo my work is complete my work is complete [1]+ Done sleep 120 -bash-4.1$
The sleep command does nothing for the number of seconds specified in the argument. The first invocation of sleep is terminated (killed) by the impatient user typing CTRL-C. The second invocation places the command in that background, we are then able to do other work. The Done statement informs us that the command has terminated.
-bash-4.1$ sleep 360 & [1] 17761 -bash-4.1$ sleep 1000 & [2] 17766 -bash-4.1$ jobs [1]- Running sleep 360 & [2]+ Running sleep 1000 & -bash-4.1$ fg sleep 1000 ^Z [2]+ Stopped sleep 1000 -bash-4.1$ jobs [1]- Running sleep 360 & [2]+ Stopped sleep 1000 -bash-4.1$ bg [2]+ sleep 1000 & -bash-4.1$ jobs [1]- Running sleep 360 & [2]+ Running sleep 1000 & x-bash-4.1$ fg %1 sleep 360 ^C -bash-4.1$ jobs [2]+ Running sleep 1000 & -bash-4.1$
In this example we put two jobs into the background. The fg command moves the last job placed in the background into the foreground. CTRL-Z stops (pauses, not kills) the job and returns to the command line. the bg command places the paused job in the background. fg can bring specific jobs to the foreground by specifying the job number.
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