1. UNIX Shell Script (2) Dr. Tran, Van Hoai Faculty of Computer Science and Engineering HCMC Uni. of Technology hoai@cse.hcmut.edu.vn

2. Dr. Tran, Van Hoai 2007 UNIX Shell Script Compound commands list = sequence of commands separated by " | ", " ; ", " & ", " && ", " || ", new line (list) executed in a subshell { list; } executed in current shell (whitespaces separated) ((expression) expression evaluation [[ expression ]] conditional expression evaluation (whitespaces needed)

3. Dr. Tran, Van Hoai 2007 UNIX Shell Script Examples (1) $ [[ "aaa" == "bbb" ]] && ls do not list anything $ [[ "aaa" != "bbb" ]] && ls list current directory $ [[ ("a" == "b")||(0==0) ]] && ls list current directory

4. Dr. Tran, Van Hoai 2007 UNIX Shell Script for command (1) for name [ in word ] ; do list ; done name is expanded to list of elements name is assigned each element, then execute list each time if no [ in word ], arguments are used

5. Dr. Tran, Van Hoai 2007 UNIX Shell Script Example (2) $ for x in `ls`; do echo $x; done list the current directory $ for x; do echo $x; done list arguments $ for x in 10, 11, 12; do echo $x; done list 10, 11, 12

6. Dr. Tran, Van Hoai 2007 UNIX Shell Script Example (3) Homework 2 #!/bin/bash files=`ls $1` for f in $files do nf=`echo $f | tr "[A-Z]" "[a-z]"` mv -f $f $nf 2>/dev/null || echo "Error renaming file $f" done

7. Dr. Tran, Van Hoai 2007 UNIX Shell Script Example (4) #!/bin/sh ############################## for files do fl=`ls $files` for f in $fl do nf=`echo $f | tr "[A-Z]" "[a-z]"` mv -f $f $nf 2>/dev/null done Homework 2 but for list of files in argument

8. Dr. Tran, Van Hoai 2007 UNIX Shell Script for command (2) for (( expr1 ; expr2 ; expr3 )) do list done Like C, java

9. Dr. Tran, Van Hoai 2007 UNIX Shell Script Example (5) Compute factorial #!/bin/sh ############################## fac=1 for (( x=1; x<=$1; x++ )) do fac=$(( $fac * $x )) done echo $fac

10. Dr. Tran, Van Hoai 2007 UNIX Shell Script if command (1) if list; then list; [ elif list; then list; ] … [else list; ] fi exis status of the last command, or 0 if no condition is tested true

11. Dr. Tran, Van Hoai 2007 UNIX Shell Script Conditional expression -a file True if file exists -d file True if file exists and is a directory -f file True if file exists and is a regular file -h file True if file exists and is a symbolic link -[rwx] file True if file exists and is readable, writable, or executable -z string True if length of string is zero ==, !=, String comparison -eq, -ne, -lt, -le, -gt, -ge Arithmetic comparison

12. Dr. Tran, Van Hoai 2007 UNIX Shell Script Example (6) Homework 2 + only process regular files #!/bin/bash files=`ls $1` for f in $files do if [ -f $f ]; then nf=`echo $f | tr "[A-Z]" "[a-z]"` mv -f $f $nf 2>/dev/null || echo "Error renaming file $f" fi done

13. Dr. Tran, Van Hoai 2007 UNIX Shell Script while, until commands while list; do list; done performs until last command in while list return non-zero until list; do list; done performs until last command in while list return zero

14. Dr. Tran, Van Hoai 2007 UNIX Shell Script Example (7) #!/bin/bash while read line do f1=`echo $line | tr " " "\t" | cut –f1` f2=`echo $line | tr " " "\t" | cut –f2` sum=$(($f1+$f2)) echo $sum done < $1

15. Dr. Tran, Van Hoai 2007 UNIX Shell Script case command case word in [ [(] pattern[|pattern]…) list; ]…esac word is expanded After the first match, no subsequent marches are executed If no pattern matches, exit status=0. Otherwise, exit status = that of last command

16. Dr. Tran, Van Hoai 2007 UNIX Shell Script Example (8) #!/bin/bash verbose=0 archive=0 for arg; do case "$arg" in -v) verbose=1 ;; -a) archive=1 ;; -h) echo "Usage: script4.sh -a -v -h " exit ;; esac done

17. Dr. Tran, Van Hoai 2007 UNIX Shell Script Assignment Write a script to compute columns (given on arguments) with 3 options  "-h" : shows usage  "-s" : shows values of columns Example  script.sh –s 1 2 3 results.txt

18. Dr. Tran, Van Hoai 2007 UNIX Shell Script Array (1) One-dimensional No maximum limit on size Indexed using integers and zero-based Explicitly declare an array declare –a name Implicitly declare an array name[subscript]=value

19. Dr. Tran, Van Hoai 2007 UNIX Shell Script Array (2) Assignment myarray=([1]=5 [3]=6 [4]="hello") Reference echo ${myarray[4]} Length of array echo ${#myarray[*]} Destroy an array unset myarray unset myarray[3]

20. Dr. Tran, Van Hoai 2007 UNIX Shell Script Function [ function ] name () compound- command [redirection] Compound-command = list of commands between { and } Exit status = that of last command Define a local variable local myvar

21. Dr. Tran, Van Hoai 2007 UNIX Shell Script Example (9) #!/bin/bash myfac(){ local fac=1 x for (( x=1; x<=$1; x++ )) do fac=$(( $fac * $x )) done echo $fac } echo `myfac $1`

22. Dr. Tran, Van Hoai 2007 UNIX Shell Script Exercise Write a script to sort list of names (countries) alphabetically $ myscript.sh Vietnam USA Ukraina Russia Russia Ukraina USA Vietnam

23. Dr. Tran, Van Hoai 2007 UNIX Shell Script Homework Write a script to show a menu for repeated tasks Can we write a script to perform linear algebra operations ?

24. Dr. Tran, Van Hoai 2007 UNIX Shell Script Regular expressions is NEXT