UNIX Shell Script (1)

1. UNIX Shell Script (1) Dr. Tran, Van Hoai Faculty of Computer Science and Engineering HCMC Uni. of Technology hoai@cse.hcmut.edu.vn

2. What is a shell script? • A series of OS commands for execution • Stored in a text file #!/bin/sh rm -f /tmp/listing.tmp > /dev/null 2>&1 touch /tmp/listing.tmp ls -l [a-z]*.doc | sort > /tmp/listing.tmp lpr -Ppostscript_1 /tmp/listing.tmp rm -f /tmp/listing.tmp

3. Shell in use (sh, bash, csh) Command Comment Components of a script #!/bin/sh rm -f /tmp/listing.tmp > /dev/null 2>&1 touch /tmp/listing.tmp # This is a comment ls -l [a-z]*.doc | sort > /tmp/listing.tmp lpr -Ppostscript_1 /tmp/listing.tmp rm -f /tmp/listing.tmp

4. How to invoke a script • Correct way $ /bin/bash my_script arg_1 arg_2 • Simple way $ my_script arg_1 arg_2 • The first line specifying the shell must be provided in simple way

5. How to be helped • Man pages hoai@moon:~> man bash ... hoai@moon:~> man sh ...

6. Definitions • Blank = chunk of tab or space • Name = sequence of ASCII letters, digits, underscores, beginning with a letter or underscore • Argument = string supplied on command-line

7. Example (argument) (1) #!/bin/sh ############################## echo "Script name is [$0]" echo "First argument is [$1]" echo "Second argument is [$2]" echo "This process ID is [$$]" echo "This argument count is [$#]" echo "All arguments [$@]"

8. Example (argument) (2) hoai@moon:~> my_script.sh hoai 1 university Script name is [my_script.sh] First argument is [hoai] Second argument is [1] This process ID is [5401] This argument count is [3] All arguments [hoai 1 university]

9. Filename metacharacters

10. Simple regular expressions (Korn shell) • Pattern = sequence of patterns separated by “|”

11. Example (metacharacters) List files having prefix new $ ls new* Cat files having prefix ch and one more letter $ cat ch? Vi files starting by letters from D to E $ vi [D-R]* Print files not *.o and core (Korn shell) $ pr !(*.o|core) | lp

12. Quoting

13. Example (quoting) $ echo 'my class is "unix and tools"' My class is "unix and tools" $ echo "Well, isn't that \"good\" ?" Well, isn't that "good" ? $ echo "You have `ls | wc –l` files in `pwd`" You have 34 files in /home/hoai $ echo "The value of \$x is $x" The value of $x is 100

14. Variables (1)

15. Variables (2)

16. Command forms

17. Example (command forms) $ nroff file > file.txt & Format in the background $ cd; ls Execute sequentially $ (date; who; pwd) > logfile All output is redirected $ sort file | pr -3 | lp Sort file, page output, then print $ vi 'grep -l ifdef *.c' Edit files found by grep $ grep XX file && lp file Print file if it contains the pattern; $ grep XX file || echo "XX not found" otherwise, echo an error message

18. Simple commands

19. Example (script) (1) #!/bin/bash alphabet="a b c d e" # Initialise a string count=0 # Initialise a counter for letter in $alphabet # Set up a loop control do # Begin the loop count=`expr $count + 1` # Increment the counter # Display the result echo "Letter $count is [$letter]" done

20. Example (script) (2) alphabet="a b c d e" # Initialise a string count=0 # Initialise a counter while [ $count -lt 5 ] # Set up a loop control do # Begin the loop count=`expr $count + 1` # Increment the counter # Position of next letter position=`bc $count + $count - 1` letter=`echo "$alphabet" | cut -c$position-$position` # Get next letter # Display the result echo "Letter $count is [$letter]" done

21. Homeworks (1) • Write a script for C compiler • Objective: use gcc by default, if gcc is not availablle, find another compiler (ending with cc) instead. • Write a script to convert filenames to lowercase letters • Input: a directory path string • Output: all filenames in the directory in lowercase

22. Homeworks (2) • Write a script to warn users using too much space • Objective: find all users of the system (/etc/passwd, cut), check if someone uses > 1GB, mail him a warning message

23. Conditional structure • Loop structure • Function • File input/output • Array are NEXT