代写 C Java math python shell compiler Go Shells Bash shell: practical uses for your systems skills Activity

Shells Bash shell: practical uses for your systems skills Activity
CSCI2467: Systems Programming Concepts
Class activity: bash shell literacy Instructor: Matthew Toups
Spring 2019

Shells Bash shell: practical uses for your systems skills Activity
Today
1 Shells History
Usage
Scripts vs. Programs
2 Bash shell: practical uses for your systems skills Computing your score so far
More common tools
3 Activity
Make a shell script

Shells Bash shell: practical uses for your systems skills Activity
Linux process hierarchy
Carnegie Mellon
Linux Process Hierarchy
Daemon e.g. httpd
Child
Grandchild
[0] init [1]
Login shell … Child
Grandchild
Login shell Child
Note: you can view the hierarchy using the Linux pstree command
Bryant and O’Hallaron, Computer Systems: A Programmer’s Perspec;ve, Third Edi;on 4

Shells Bash shell: practical uses for your systems skills Activity History
Shell
A shell is an application program that runs programs on behalf of the user.
– sh Orig. Unix shell (Stephen Bourne, AT&T Bell Labs, 1977) – csh / tcsh BSD Unix C shell (1978 / 1981)
1978: UC Berkeley grad student Bill Joy
(vi, Sun Microsystems, Java language)
– bash GNU “Bourne-Again” Shell (1989)
default Linux shell (1991), default macOS shell (since 10.3, 2003)
Windows 10 (Anniversary update, 2016) – tsh “tiny” shell (you, 2017)

Shells Bash shell: practical uses for your systems skills Activity Usage
bash is used in many ways
Command processor, or programming language?

Shells Bash shell: practical uses for your systems skills Activity Usage
bash is used in many ways
Command processor, or programming language? Both!

Shells Bash shell: practical uses for your systems skills Activity Usage
Interactive vs. scripting
Interactive case: human types commands at a prompt – You’ve been using bash this way.
– Your tsh will work this way.

Shells Bash shell: practical uses for your systems skills Activity Usage
Interactive vs. scripting
Shell script: any commands you could type at the shell
prompt could also go into a file
– bash then interprets that file as a sequence of commands – thie file is typically called a script
(denoted by .sh filename extension)

Shells Bash shell: practical uses for your systems skills Activity Usage
Interactive vs. scripting
bash as Command Processor
Interactive case: human types commands at a prompt – You’ve been using bash this way.
– Your tsh works this way.
bash as Programming language
Shell script: any commands you could type at the shell
prompt could also go into a file
– bash then interprets that file as a sequence of commands – thie file is typically called a script
(denoted by .sh filename extension)

Shells Bash shell: practical uses for your systems skills Activity Scripts vs. Programs
Script? Program? What’s the difference?
scripts are text files which are interpreted
– Scripting languages: bash, perl, python (many more)
– An interpreter reads script text every time it runs and then performs commands
Traditional programming languages are compiled
– A compiler converts human-readable source code to
machine-level instructions (may be called binary or executable)
– These machine-level instructions are the focus of Chapter 3

Shells Bash shell: practical uses for your systems skills Activity Scripts vs. Programs
Shell scripting

Shells Bash shell: practical uses for your systems skills Activity Computing your score so far
Your point total
As usual, log on to terminal in Math 209/212 or via ssh to systems-lab.cs.uno.edu

Shells Bash shell: practical uses for your systems skills Activity Computing your score so far
Your point total
Change to your 2467 directory:
cd 2467
Create files called:
SCORE.midterm SCORE.lab0 SCORE.lab1 SCORE.lab2
Can view all with:
cat SCORE.*
… and add up with:
cat SCORE.* | ../sum.sh

Shells Bash shell: practical uses for your systems skills Activity Computing your score so far
What did we just do?
No felines were harmed
cat command concatenates files
output contents of each file given in order
if only one filename given (singleton), then simply output contents of that file

Shells Bash shell: practical uses for your systems skills Activity Computing your score so far
What did we just do?
wildcards, or “globbing”
Bash looked in the current directory for files that match the pattern: SCORE.*
* is a wildcard: matches anything (zero or more characters) Therefore SCORE.* matches any file which begins with
SCORE.
As in, all of your scores:
SCORE.lab0 SCORE.lab1 SCORE.lab2 SCORE.midterm bash does this, so the cat program thinks you typed: cat SCORE.lab0 SCORE.lab1 SCORE.lab2 SCORE.midterm
– wildcards won’t work in tsh or tshref
– so in tsh you would see this:
/bin/cat: SCORE.*: No such file or directory

Shells Bash shell: practical uses for your systems skills Activity Computing your score so far
What did we just do?
more on wildcards
Could also match a single character:
cat SCORE.lab?
– Would match SCORE.lab9 but not SCORE.lab10
Or, match only certain characters:
cat SCORE.lab[01]
– matches only SCORE.lab0 and SCORE.lab1
(not SCORE.lab2) or any others

Shells Bash shell: practical uses for your systems skills Activity Computing your score so far
What did we just do?
more on wildcards
Try creating a SCORE.lab10 file with:
echo 100 > SCORE.lab10
– remember output redirection? Then compare:
cat SCORE.lab?
cat SCORE.lab??
cat SCORE.lab*
Delete SCORE.lab10 when finished: rm SCORE.lab10
Be very careful using * with rm !

Shells Bash shell: practical uses for your systems skills Activity Computing your score so far
What did we just do?
Pipes
| is called a “pipe”
– cmd1 output normally goes to the screen
… but instead becomes cmd2 input (another type of redirection)
– Then cmd2 output goes to screen
… but could be written to a file:
cmd1 | cmd2 > outputfile
Many more examples on Bash redirections cheat sheet

Shells Bash shell: practical uses for your systems skills Activity Computing your score so far
What did we just do?
Shell script example
#!/bin/bash
TOTAL =0
while read val; do
TOTAL=$(($TOTAL+$val)) echo $TOTAL
done
sum.sh is a shell script (text file)
commands interpreted by program /bin/bash would also work if typed in at the prompt:
TOTAL=0;
while read val; do TOTAL=$(($TOTAL+$val)); done;
echo $TOTAL

Shells Bash shell: practical uses for your systems skills Activity Computing your score so far
What did we just do?
stdin
sum.sh run by itself takes input from keyboard (each number on its own line, end with CTRL-D) file descriptors 0, 1 and 2 commonly referred to as: stdin, stdout, stderr
Images from http://www.catonmat.net/blog/bash-one-liners-explained-part-three/

Shells Bash shell: practical uses for your systems skills Activity Computing your score so far
What did we just do?
stdin
Thanks to the pipe we used, instead the input to the sum program came from those SCORE.* files
(actually sum.sh didn’t read files, it read the output of cat) keeps sum.sh program very simple
Also works with C programs (file descriptors 0 and 1, open() and dup2())
Images from http://www.catonmat.net/blog/bash-one-liners-explained-part-three/

Shells Bash shell: practical uses for your systems skills Activity More common tools
grep: print lines matching a pattern
Make yourself a copy of this example file:
cp /home/CSCI2467/labs/bash/lab0−comments .
Then run:
grep part lab0-comments
strange name, used as noun or verb
simple and very useful
example above: find any line containing “part” in file lab0-comments (contains several lines)
– case sensitive! try with Part instead
(try with option -i for insensitive)
could write result to a file with:
grep Part lab0-comments > mylab0parts
grep photoshoot by Christiaan Colen

Shells Bash shell: practical uses for your systems skills Activity More common tools
Pipes make grep even more useful

Shells Bash shell: practical uses for your systems skills Activity Make a shell script
Extra credit opportunity
Go to AutoLab
– look for extra credit bash scripting
the writeup is these slides
(at the end of the PDF files) the handout is called grep.tar

Shells Bash shell: practical uses for your systems skills Activity Make a shell script
Extra credit opportunity
Add up to 5 points to your point total
Create a shell script called secretfinder.sh which:
– create a directory called secretfiles and change into it
– extrace files from grep.tar
– use grep command to find which file contains the SECRET AUTH CODE
– write the name of that file to a new file called: authcode.txt
– remove the 1000 files tar created (but leave authcode.txt)1
– print “Found the secret auth code! Saved to authcode.txt” to the screen (not to the authcode.txt file)
Hand in your solution (only secretfinder.sh) using AutoLab
1Again be careful with rm and see tips on next page

Shells Bash shell: practical uses for your systems skills Activity Make a shell script
Some tips
Begin your file (the very 1st line) with #!/bin/bash
– after that you can comment each line using the # symbol
– put your name and the date in a comment at the top
– comment subsequent commands
To extract files use:
tar xf grep.tar
To delete the 1000 files, use rm f*==
notice how the above command should only delete files that start with “f” and end with “==”

Shells Bash shell: practical uses for your systems skills Activity Make a shell script
Scoring
Total 5 points
– 1 point: file is named properly, begins with interpreter line, valid comments for each line
– 1 point: created directory and extracts files
– 1 point: finds AUTH CODE
– 1 point: writes AUTH CODE to correct file
– 1 point: cleans up 1000 files and prints only one line of output.

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