Library functions

2. Library functions • We do not have to run everything as a script • We may have an interesting function we make available. • There is an analogy with Java  • Just like a public library we can borrow from. • Typically store these in a lib/ directory.

3. ~/lib/libFunction.txt • cat ~lib/libFunction.txt • scope () #function name • { #function body • echo this is a library function • }

4. ~/lib/libFunctionArg.txt • myEchoArg () • { • echo I hope you supplied an argument • echo $1 • echo $0 • }

5. My script calls library functions. • #! /bin/bash • # this defines the path to the function • . ~/lib/libFunction.txt • . ~/lib/libFunctionArg.txt • scope • myEchoArg thisone • myEchoArg thatone

6. sh libCalling.sh – the output. • sh libCalling.sh • this is a library function • I hope you supplied an argument • thisone • libCalling.sh • I hope you supplied an argument • thatone • libCalling.sh

7. Do Aliases work in a script? • $ ls • a.txt b.txt c.txt remove.sh remove.sh~ • $ rm a.txt • rm: remove regular empty file `a.txt'? y • $ sh remove.sh • $ ls • remove.sh remove.sh~

8. type which whereis • type ls • type pwd • which • whereis

9. Expanding arguments 1 • # run this script with different arguments. • #sh argsExpand.sh a b c d • #sh argsExpand.sh a b 'c d' • #sh argsExpand.sh a b "c d"

10. Expanding arguments 2 for arg in $* • do • echo $arg • done • for arg in "$@" • do • echo $arg • done

11. Logical and if [ arg1 -a arg2 ] • then • echo 1 • else • echo 2 • fi

12. Short circuit • if [ true ] && [ true ] • then • echo 1 • else • echo 2 • fi

13. This does not work • if [ true && true ] • then • echo 1 • else • echo 2 • fi

14. Logical or • if [ true -o true ] • then • echo 1 • else • echo 2 • fi

15. Logical or • if [ true -o true ] • then • echo 1 • else • echo 2 • fi

16. Short circuit • if [ true ] || [ true ] • then • echo 1 • else • echo 2 • fi

17. This does not work • if [ true || true ] • then • echo 1 • else • echo 2 • fi

18. Communication • mailx • mesg • write • talk

19. mailx • $ mailx -s hi zlizjw1 • Hi John Hope you are doing okay • press ctrl d to end message • Cc: zlizjw1 • /usr/sbin/sendmail: Permission denied • $ mailx • No mail for zlizjw1

20. Mesg 1 • 'y' and 'n' options respectively allow and disallow write access to your terminal. • the permission other users have to write to your terminal using the talk and write commands

21. Mesg 2 • $ mesg • is y • $ mesg n • $ mesg n • $ mesg • is n • $ mesg y • $ mesg • is y

22. write • The correct syntax for the write command is: • write user [tty] message • $ write zlizjw1 • hi there, fancy a coffee in 10 minutes? • Message from zlizjw1@unnc-cslinux.nottingham.edu.cn on pts/20 at 16:27 ... • hi there, fancy a coffee in 10 minutes? • EOF

23. Wait 1 • echo start of first loop > output.txt • for i in 1 2 3 4 5 • do • echo i = $i >> output.txt • done &

24. Wait 2 • #$! is the process ID of the last process • echo $! • lastprocessID=$! • #this will wait for that process to end. • wait $lastprocessID

25. Tee for two? • echo hi (this goes to screen) • echo hi > file1.txt (this goes to file1.txt ) • echo hi | tee file1.txt (sends to screen and file1.txt) • echo hi | tee file1.txt file2.txt (sends to screen and file1.txt file2.txt)

26. Tee –a (append) • echo hi | tee -a file1.txt • This will append • Question • How would you stop tee from printing to screen?

27. answer • This will stop the print to screen • { echo hi| tee file1.txt file2.txt;} > /dev/null

28. No clobber - append • set –o noclobber • echo “even more” >| myfile.txt • echo >> myfile.txt • This still works.

29. Octal dump • $ echo "a b c d" >| a.txt • $ od a.txt • 0000000 020141 020142 020143 005144 • 0000010 • Usually very long – so pipe into head • od file.txt| head

30. Octal dump • -c will give the characters. • echo "a b c" > file.txt • $ od -c file.txt • 0000000 a b c \n • 0000006

31. nohup • If you have a big program you do not want to stop when you log off? • java bigProgram& • nohup java bigProgram & • (nohup = no hang up – like a telephone)

32. What does this print on screen? • if true && true • then • echo it's true • else • echo it's false • fi

33. if • true • false • then • echo "its true" • else • echo "its false" • fi

34. if true false • then • echo "its true" • else • echo "its false" • fi

35. time • $ time sleep 5 • real 0m5.004s • (real time elapsed) • user 0m0.000s • (time spent processing user’s command) • sys 0m0.002s • (time spent by system, e.g. moving processes)

36. Check sum • If you sender and reciever have a file, how can they be sure the file is not corrupted by noise. • Checksum will generate a number (two), and if the numbers at the same then they can be confident that the message was not corrupted.

37. Check sum • []$ echo hi | cksum • 1479881546 3 • []$ echo hi | cksum • 1479881546 3 • []$ echo Hi | cksum • 3000792507 3

38. Path check 1 • pathchk -p my12345678901234567890.sh • pathchk: name `my12345678901234567890.sh' has length 25; exceeds limit of 14 • The –p is for portability.

39. Path check 2 • $ pathchk a/a.txt • [zlizjw1@unnc-cslinux LAB]$ cat a/a.txt • this • [zlizjw1@unnc-cslinux LAB]$ chmod 000 a • [zlizjw1@unnc-cslinux LAB]$ pathchk a/a.txt • pathchk: directory `a' is not searchable

40. rm -file • How to remove a file with a dash at the start? • Unix/linux thinks it’s an option!!! • $ rm -a.txt • rm: invalid option -- a • Try `rm --help' for more information. • So lets try this • rm ./-a.txt • find ./ -name –a.txt -exec rm -f {} \;