Part 1: Basic Commands/Utilities

1. Part 1: Basic Commands/Utilities

2. Basic Utilities • ls, cat, echo • ls -l • e.g., regular file or directory, permissions, file size • ls -a • cat file1 file2 file3 … • echo “hello world” > file • echo $VAR, echo hello* • echo –n “hello world”

3. Basic Utilities • more, less, head, tail • head -5 file • tail -3 file • pwd, cd • cp, mv, rm, mkdir, rmdir • ‘-i’ option • ‘-r’ option: rm –r dir1 • rmdiran empty directory

4. Basic Utilities • sort, wc, grep, |(pipe) • wc -l file, wc –c file • grep “keyword” file • grep -v • sort linux | head -5 • bzip2, gzip, tar (no compression)

5. Questions ‘cp –r dir1 dir2’ makes dir2 identical to dir1. True / False Which of the following commands can display the value of the present working directory? • pwd • echo $PWD • echo $(pwd) • pwd | echo • pwd| cat

6. Questions Utilities head and tail can display the first or last several lines of a file. Explain the function of “head -8 file | tail -4”.

7. Part 2: File Systems

8. Filename and Path • Hierarchical tree structure • Absolute path name • ls /home/it244/it244 • Relative path name • cd /home/it244 • ls it244 • ‘.’ ‘..’ ‘~’ • ‘*’ ‘?’ • echo hello*, echo ./.?a*

9. Access Permissions • r, w, x (chmod) • chmoda+rw file • chmod a=rx file • chmod 644 file • Execute permission of a directory • A directory is a table of files (filename:meta) • Executable means searchable

10. Access Permissions • Operations on book/book1 • ls book/book1 • book ( x ) • cat book/book1 • book1 ( r ), book ( x ) • rm book/book1 • book ( xw ), book1 ( w )

11. Links • Hard link and soft link • Hard link cannot refer to a directory • Soft link can point to a nonexistent file $ ln -s hello hello.sl $ rm hello $ echo “new” > hello $ cat hello.sl new

12. Questions Both hard links and symbolic links can refer to directories. True / False Assume there are the following files: $ls a b c abbcac abccbaacbabcd How many files are listed as the output of “echo a?*” :

13. Questions Assume there is a directory ‘dir1’ containing one file ‘file1’. To rename ‘dir1/file1’ to ‘dir1/file2’ , what permissions are needed and why?

14. Part 3: Bash/Shell Scripting

15. Execute Commands • Foreground and background jobs • command &, CTRL+Z • difference between a suspended job and a background job, PID • jobs, ps, kill, bg, fg • Group commands • (cmd1; cmd2; cmd3)

16. Redirection • Standard input, output, error output • cat file1 file2 > out 2>err • cat file1 file2 &> out • cat file1 file2 > out 2>&1 • Redirected output will not be displayed on the screen.

17. Variables • System variables • $PATH, $PWD, $HOME • User defined variables • VAR=hello • export VAR=hello • declare; declare -x

18. Variables • New shell for executing a script $cat script1 echo $VAR VAR=new echo $VAR $VAR=old;./script1;echo $VAR $VAR=new ./script1;echo $VAR $export VAR=old;./script1;echo $VAR

19. Expansion/ Quote • Types • echo hello*; echo ~ • echo $VAR • echo $(pwd) • echo $((1+1)) • VAR=hello* • echo $VAR • Single quote suspends all expansions

20. Alias • Short names • alias rm=‘rm –i’ • alias ll=‘ls –l’ • alias mypwd1=“echo pwd is $PWD” • alias mypwd2=‘echo pwd is $PWD’

21. Control Flow if..then..fi, if..then..else, while test-command do commands done for loop-index in argument-list do commands done

22. Control Flow • Conditions • test $# -eq 0 • [ -f “$1” ] • [ condition1 –a condition2 ], -o • [[ && ]], (( || )) • Exit status $? • if [ read <file $line ] …

23. Control Flow • Boolean operators • Short circuiting $((a=2, b=2)) $((a++ || b--)) $echo $a $b $((--a>2 || b++)) $echo $a $b

24. Questions If we execute the following sequence of commands in order, what are the values of variables a, b and the output AFTER executing each line? $((a=1, b=2)) $echo $((a-- + b++))a=_0_, b=_3_, output=_3_ $echo $((a++ + ++b)) a=_1_, b=_4_, output=_4_

25. Questions If we execute the following sequence of commands in order, what are the values of variables a and b AFTER executing each line? $ ((a=0, b=1)) $ ((a++ || b--)) a=_1_, b=_0_ $ ((++b || ++a))a=_1_, b=_1_

26. Variables • Arguments • $1-$n, $0, $#, $@ • set set a 123 hello echo $1 $2 $3 set $(date) • shift echo $@ shift echo $@ • $$, $?

27. Variables • Undefined variables • ${name:-default}, ${name:=default}, ${name:?message} echo ${VAR:-hello} echo ${VAR:=world} echo ${VAR:=world} echo ${VAR:-hello}

28. File I/O • exec exec 3 < infile exec 4 > outfile • read • read -p “Enter sth: ” input1 input2 • read <&3 line, read –u3 line • Determine the end of a file • $line has no value • ‘read’ returns false • Write to a file • echo “abc” >&4

29. Expressions • Arithmetic • a=5;b=3;echo $((a%b)) • echo $((a+++3)) • Logic • cat abc && ls • echo $?

30. Part 4: Perl/AWK

31. Run a Program • Perl • perl simple.pl • perl –e ‘print “hi\n”’ • AWK • gawk -f simple file • gawk ‘/chevy/ {print}’ file Stand-alone scripts #!/usr/bin/perl #!/usr/bin/gawk -f

32. Regular Expressions • Patterns • perl • ., \d, \D • *, + .* • “aged”=~/a..d/ • AWK • $1 ~ /a..d/ • Search and replace (perl) • s/\/usr//

33. Regular Expressions • Brackets in perl • $str=“10 + 20” • $str=~/(\d+).*(\d+)/ • print $1+$2

34. File I/O in perl • Read open ($infile, '<', “filename”); while ($line=<$infile>){ print $line; } $line=<> • Write $filename="./log"; open($outfile,'>',$filename); print $outfile "Hello world!\n";

35. Questions • Assume there is a file file1 containing one line Col1 Col2 Col3 Which of the following commands outputs ‘Col2’ • $set $(cat file1); echo $2 • $gawk ‘{print $2}’ file1 • $perl-e '$line=<>; $line=~ s/.* (.*) .*//; print "$1\n"' < file1

36. Questions • Read the following shell script and answer the questions $cat script1 #!/bin/bash exec 3<$1 exec 4<$2 exec 5>$3 while read line <&3 do echo “$line” >&5 done while read line <&4 do echo “$line” >&5 done • Q1. The script requires 3 filenames as arguments, e.g., • ./script1 file1 file2 file3 • Which files are input files and which are output files? • Q2. Inside the while-loop, why variable “$line” has to • be enclosed by double quotes?