CSE4251 The Unix Programming Environment

1. CSE4251 The Unix Programming Environment Lecture 4 Shell environment III: - command alias & history; job control; editor (vim)

2. Recap • Shell environment II • I/O redirection & pipe: <, >, >>, 2>, 2>>, 2>&1, |, tee • building complex commands: &, ;, ?, &&, ||, • shell variables: e.g., exportPATH in ~/.bashrc • Lab1: DUE 11:59pm, Monday, Sept 29, 2014

3. alias • shortcuts for long/complex commands • set alias: $ alias short_name=‘long_complex_command’ E.g., $ alias lm=‘ls –l | more’ #ls page by page E.g., $ alias rm=‘rm –i’ #prompt before every removal E.g., simulate DOS commands cls and dir : $ alias cls=‘clear’ #clear the screen$ alias dir=‘ls -l’

4. alias • shortcuts for long/complex commands • show all aliases defined: $ alias [23:58:29][zhengm@apollo-tesla:~] $ alias ... alias ls='ls --color=auto' alias ll='ls -l --color=auto‘ alias vi='vim‘ alias cdmy='cd /home/zhengm/0repos/emulator-iscsi/pfe_apps/MySQL‘ ...

5. alias • shortcuts for long/complex commands • unset alias: unalias $ unalias lm $ unaliasrm $ unaliascls $ unalias dir • difference b/w alias and variable • aliases are used directly as “new” commands • variables are used as part of other commands (e.g., echo $SHELL)

6. command history • shell saves recently used commands • list all saved commands: $ history or, use alias to save some typing in the future: $ alias h=‘history’ $ h • list N most recent commands: $ history N $ history 3 • size of history: $ echo $HISTSIZE $ history 3 1003 history 1004 vim ~/.bash_history 1005 history 3 $ echo $HISTSIZE 1000

7. command history • invoke previously used commands • execute the last command again: $ !! • execute a command based on cmd#: $ !cmd_number E.g., $ !1005 #equal to $ man rm • execute a command based on (partial) name: $ !cmd_name E.g., $ !al #the last command begin w/ “al” #equal to $ alias • where is history stored: ~/.bash_history $ history ... 1005 man rm 1006 alias 1007 man history 1008 history

8. Job control • The shell allows you to run/manage multiple jobs in one terminal • place jobs in the background • you can have multiple background jobs • two background states: stopped and running • move a job to the foreground • you can have only one foreground job (in one terminal) • suspend a job • kill a job • get information about a job

9. Background jobs • If you follow a command with "&", the shell will run the job in the background • don't need to wait for the job to complete, you can type in a new command right away • can have a bunch of jobs running in the background E.g., start a background job: $ tar -zvcf/tmp/etc.tar.gz /etc & [1] 7507 run in background job # PID (process# )

10. Background jobs • If you follow a command with "&", the shell will run the job in the background • don't need to wait for the job to complete, you can type in a new command right away • can have a bunch of jobs running in the background E.g., when the background job completes: [1]+ Done tar -zvcf/tmp/etc.tar.gz /etc job # finished successfully the cmd for the job

11. Background jobs • If you follow a command with "&", the shell will run the job in the background • don't need to wait for the job to complete, you can type in a new command right away • can have a bunch of jobs running in the background • still output to the screen by default (stdout & stderr); • use I/O redirection to save stdout/stderr in log file and thus avoid interference $ tar -zvcf/tmp/etc.tar.gz /etc > /tmp/log.txt 2>&1 & [1] 7529

12. Background jobs • Throw a job into background (suspend a job) • [ctrl]-z • List current background jobs • $ jobs [17:41:57][zhengm@apollo-tesla:~] $ vi ~/.bashrc [1]+ Stopped vim ~/.bashrc [18:04:24][zhengm@apollo-tesla:~] $ $ jobs -l [1]+ 7903 Stopped vim ~/.bashrc

13. Background jobs • make a stopped background job run in background • $ bg %job_number • bring a background job to foreground • $ fg %job_number E.g. $ fg %1 [17:41:57][zhengm@apollo-tesla:~] $ vi ~/.bashrc [1]+ Stopped vim ~/.bashrc [18:04:24][zhengm@apollo-tesla:~] $ fg %1

14. Kill jobs • kill the foreground job • [ctrl]-c • kill a background job • $ kill –signal %job_number E.g., $ kill -9 %1 • Check signals • $ kill –l E.g., 9) SIGKILL 15) SIGTERM $ jobs [1]+ Stopped vim ~/.bashrc [18:30:12][zhengm@apollo-tesla:~] $ kill -9 %1; jobs [1]+ Stopped vim ~/.bashrc [18:30:30][zhengm@apollo-tesla:~] $ jobs [1]+ Killed vim ~/.bashrc [18:30:51][zhengm@apollo-tesla:~] $ jobs [18:30:58][zhengm@apollo-tesla:~] $

15. summary of job control • jobs: list current jobs • [ctrl]-z: suspends the foreground job • [ctrl]-c: kill the foreground job • bg: run the most recently suspended job in the background • fg: move the most recently backgrounded job from the background into the foreground • kill: terminate a job kill [-s signal] %job_number kill –l : list the kill signals

16. editor • recommended: either vi/vim or emacs

17. vi/vim 101 • vi exists in every Unix-like OSes • default interface for important commands/tools, e.g.: visudo #edit superuser privileges crontab #schedule auto-run programs • a “modal” editor: has two modes • edit mode: your keyboard is the one you’re familiar with (e.g., typing “i” means printing “i” on screen), just like typing in gedit or MS Word • command mode: letters have special meaning; do some special tasks (e.g., jump to line# 10,000 directly, replace all “cse4241” with “cse4251” in one go, delete 100 lines below, save and quit, ...)

18. vi/vim 101 • vim is an improved version of vi • more functionalities, easier to use • similar to ~/.bashrc, vim has a configuration file called ~/.vimrc Example configurations: set nu " show line number set nonu " no line number set tabstop=4 " numbers of spaces of tab character syntax on " syntax highlight

19. vi/vim 101 • open an file: $ vim myscript.sh cursor line# (if enabled) ~ means empty line information about file and command; default in command mode

20. vi/vim 101 • enter edit mode: type i typing “i” tells the editor you want to insert text

21. vi/vim 101 • edit text: type “hello,” [Enter], “world!” type letters normally; [Enter] to start a newline keep showing your current mode

22. vi/vim 101 • finish editing, exit edit mode and return to command mode: [Esc] after [Esc], you have returned to command mode

23. vi/vim 101 • enter a command: type :wq, then [Enter]

24. vi/vim 101 • You have successfully created, edited, and saved a file using vim [21:25:19][zhengm@apollo-tesla:~] $ ls -l myscript.sh -rw-rw-r--. 1 zhengmzhengm 14 Sep 25 21:25 myscript.sh [21:25:37][zhengm@apollo-tesla:~] $ cat myscript.sh hello, world! [21:25:51][zhengm@apollo-tesla:~] $

26. More resources • How to use vi • http://www.washington.edu/computing/unix/vi.html • http://www.openvim.com/tutorial.html • How to use Emacs • http://zoo.cs.yale.edu/classes/cs210/help/emacs.html