Let me show the power of the shell! There some things that you just can't do clicking a mouse or pecking on the keyboard stretching your fingers between letters and the
alt or
ctrl keys. Cron and at are you friends along with pipes. I work a lot on remote terminals at the command line and have become quite competent, even writing a few short scripts that do quite a lot. I'm not familiar with the latest version of Windows shell Monad so I won't compare it and just stick to what I know.
Let's try this, say you want a directory listing of everything in your home folder. Well in Windows you would open up your My Documents . But that doesn't save it in file, it just shows it to you. What about the command prompt, Start->Run->cmd enter in "
dir" and there it is. But that still isn't in a file; okay copy, open notepad, paste it in. Now you have your home folder listing in a file. Bash or csh or ksh is much easier!
cd ; ls -l >> myhome.txtThat's it.
cd changes directory to your home,
ls -l gives a directory listing in long format,
>> is the redirect command. Redirect takes the output from a command and sends it somewhere else. Usually it's used to create log files, here it takes the output and saves it in a file. Sometimes output is sent to the null device /dev/null; this will just send it nowhere. Redirect can also work the other way as in sending an input file to a command for processing.
Here is a common command I use:
ps -ef | grep db2Here I use the
pipe. Pipes are used usually in a chain of commands, the output of one command is used as the input for the next command. In the example I take the output of the
ps command, process, and send to
grep, pattern searching, looking for anything containing
db2. You can add any number of commands to chain as long as it makes sense:
tail -f `ls -tr *backup* | tail -1`This chain will get the most recently modified file that has backup in the name. The back ticks will return the commands between them. In effect
tail -f will wait for
ls -tr *backup* | tail -1 to execute and use the results in the command.
tail -1 returns the last line of
ls -tr *backup*. Adding it up the command will continously display the contents of the latest backup file
.
Normally
ps returns process sorted by their id, suppose we want the only db2 process sorted by name saved in a file:
ps -ef | grep db2 | sort >> db2process.txtLet's find out who has an account
cat /etc/passwd | cut -f 1 -d : | sortcat just spills out the contents of a file, sends the output to
cut field 1 delimited by ":" and then sends it
sort.
Command chains can become quite cryptic and long:
cd dba ; tail `ls -tr *backup* | tail -1` | (grep Finished && ls -ltr *backup*) || (tail -f `ls -tr *backup* | tail -1`)My favorite, because I wrote it, change to the dba directory and tail the most recent backup file looking for "Finished" then show the listing otherwise keep tailing the file.
More to follow...
