You may already be familiar with some redirection, such as. which saves the output of the ls command into a file called lsoutput.txt.

Transcription

1 Shell Programming A shell is a program that acts as the interface between you and the Linux system, enabling you to enter commands for the operating system to execute. In that respect, it resembles the Windows command prompt, but much more powerful You may already be familiar with some redirection, such as $ ls -l > lsoutput.txt which saves the output of the ls command into a file called lsoutput.txt. One reason to use the shell for programming is that you can program the shell quickly and simply. On Linux, the standard shell that is always installed as /bin/sh is called bash You can check the version of bash you have with the following command: Output $ /bin/bash version husaingholoom$ /bin/bash --version GNU bash, version (1)-release (x86_64-apple-darwin11) Copyright (C) 2007 Free Software Foundation, Inc. Fall 2013 CS4350 Husain Gholoom Page 1

2 Objective : What is shell (interpreted vs. complied) Variables Conditions Flow structures What is shell A Unix program executed when you log in A command interpreter provides the basic user interface to UNIX utilities A programming language program consisting of shell commands is called a shell script put commands in a file and execute it make the file executable (chmod u+x script-file ) Compiled vs. Interpreted Com piler g++/gcc Executable Fall 2013 CS4350 Husain Gholoom Page 2

3 Examples : Compiled Languages : C / C++, FORTRAN, Pascal, Cobol Interpreted Languages : Unix shell, scripts, Perl, Basic (in 80's) Shells Bourne shell Stephen Bourne at Bell Labs, 1977 C shell Bill Joy at Berkeley (Sun) More C-like interface Ken Thompson s shell Bourne sh - basic Bourne shell bsh - another basic Bourne shell bash - GNU Bourne Again shell C Shell csh - basic C shell tcsh - extended C shell What s the difference? Internal execution Basic commands (ls, cd) are same Which one am I in? echo $SHELL you will get Type exit to exit the shell /bin/bash Fall 2013 CS4350 Husain Gholoom Page 3

4 Language Components : A programming language has Variables Arrays Flow Controls If-then-else - AND - OR while do for do until do switch Classes (Unix doesn t have these) Why Use Shell? Everything can be done in C/C++ Shell scripts Really, really fast to write Use once, throw away Powerful library functions Example: show the file list in a directory and find a file with a name ABC First Shell Script Create a file hello #!/bin/sh #This is an example e echo Hello World exit 0 Execute the file chmod +x hello./hello Fall 2013 CS4350 Husain Gholoom Page 4

5 First Shell Script Lines starting with # are comments. The first line of your script file begin with: #!pathname optional arguments pathname is an absolute pathname of the interpreter (/bin/sh, or /bin/bash). The last line returns the status of the script to the system. exit 0 (successful) exit 1 (fail) Local Variables Set value var=value value is a string, even in the format of a number On the command line, you can see this in action when you set and check various values of the variable salutation: Example $ salutation=hello $ echo $salutation Hello $ salutation= Yes Dear $ echo $salutation Yes Dear $ salutation=7+5 $ echo $salutation 7+5 Fall 2013 CS4350 Husain Gholoom Page 5

6 Retrieve value Quote $var : the value ${var} : the value $var : the value as a string $var : the name \ preserves the literal value of the next character (\$1) literal value of enclosed characters ( \$1 ) " literal value of enclosed characters except: $ retains its special meaning and \ retains its special meaning when followed by $ " \ l myvar=val echo myvar echo $myvar echo myvar echo $myvar echo \$myvar echo \$$myvar echo \ $myvar\ echo \ $myvar\ myvar val myvar val $myvar $val "val" 'val' Fall 2013 CS4350 Husain Gholoom Page 6

7 Example : Create a file and type in the following #!/bin/sh myvar= Hi there echo $myvar echo $myvar echo $myvar echo \$myvar echo Enter some text read myvar echo $myvar now equals $myvar exit 0 Exit the editor Save the file Change mode ( chmod +x filename.sh ) Execute the shell (./filename.sh ) The Result is $./variable Hi there Hi there $myvar $myvar Enter some text Hello World $myvar now equals Hello World Fall 2013 CS4350 Husain Gholoom Page 7

8 Environment Variable $HOME : The home directory of the user $PATH : A colon-separated list of command directories $PS1 : The command prompt $IFS : The input string separator This is a list of characters that are used to separate words when the shell is reading input, usually space, tab, and newline characters. $SHELL : The shell interpreter Use set or env to show the environment variables Parameter Variable : If your script is invoked with parameters, some additional variables are created. If no parameters are passed, the environment variable $# still exists but has a value of 0. $? : the exit status of last process $0 : the name of the shell script $# : the number of parameters $$ : the process ID of the shell script $1,$2,... : the parameters $* : the list of all parameters, by $IFS $@ : the list of all parameters, by Fall 2013 CS4350 Husain Gholoom Page 8

9 Example : Try the following script #!/bin/sh salutation="hello" echo $salutation echo "The program $0 is now running" echo "The second parameter was $2" echo "The first parameter was $1" echo "The parameter list was $*" echo "The user's home directory is $HOME" echo "Please enter a new greeting" read salutation echo $salutation echo "The script is now complete" exit 0 If you run this script, you get the following result: husain-gholooms-macbook:shell husaingholoom$./sc5.sh Texas State University Hello The program./sc5.sh is now running The second parameter was State The first parameter was Texas The parameter list was Texas State University The user's home directory is /Users/husaingholoom Please enter a new greeting CS4350 Unix Programming CS4350 Unix Programming The script is now complete husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 9

10 Variable Shell script mytest IFS= ; echo $* echo $@ echo $0 Command./mytest arg1 arg2 arg3 Result arg1;arg2;arg3 arg1 arg2 arg3./mytest Condition Test if test condition if [ condition ] then then statements statements fi fi if test condition ; then statements fi if [ condition ]; then statements fi if [ condition ] then statements elif [ condition ] then statements else statements fi if [ condition ]; then statements elif [ condition ]; then statements else statements fi Fall 2013 CS4350 Husain Gholoom Page 10

11 Control and Condition A common use for if is to ask a question and then make a decision based on the answer: For Example : Script mytest #!/bin/sh echo "Is it morning? Please answer yes or n" read timeofday if [ $timeofday = "yes" ]; then echo "Good morning" else echo "Good afternoon" fi exit 0 Run the script by typing the following Command husain-gholooms-macbook:shell husaingholoom$./mytest.sh The Result is Is it morning? Please answer yes or n yes Good morning husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 11

12 Condition String comparison string1 = string2 string1!= string2 -n string -z string True if The strings are equal The strings are not equal The string length is not zero The string length is zero (NULL or Empty String ) Arithmetic Expression expr1 -eq expr2 expr1 -ne expr2 expr1 -gt expr2 expr1 -ge expr2 expr1 -lt expr2 expr1 -le expr2!expr File condition -e file -d file -f file -r file -w file -x file -s file True if equal not equal greater than greater than or equal to less than less than or equal to false Treu if exist directory regular file readable writable executable non-zero size Fall 2013 CS4350 Husain Gholoom Page 12

13 Example : Script mytest #!/bin/sh if [ -f /bin/bash ] then echo "file /bin/bash exists" fi if [ -d /bin/bash ] then echo "/bin/bash is a directory" else echo "/bin/bash is NOT a directory" fi Run the script by typing the following Command husain-gholooms-macbook:shell husaingholoom$./mytest.sh The Result is file /bin/bash exists /bin/bash is NOT a directory husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 13

14 for variable in values do statements done Script mytest For Loop #!/bin/sh for file in $(ls *.*) ; do echo "This is $file" done Run the Script by using the following Command./mytest The Result is This is sc1.sh This is sc2.sh This is sc3.sh This is sc4.sh husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 14

15 When condition is true, loop while condition do statements done While Loop Script sc7.sh #!/bin/sh echo "Enter password" read trythis while [ "$trythis"!= "secret" ]; do echo "Sorry, try again" read trythis done exit 0 After you change the mode, Use the following command to run the script The Result is husain-gholooms-macbook:shell husaingholoom$./sc7.sh Enter password secrete Sorry, try again secret husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 15

16 Until Loop When condition is not true, loop until condition do statements done Script sc8.sh #!/bin/sh COUNTER=20 until [ $COUNTER -lt 10 ]; do echo COUNTER $COUNTER let COUNTER-=1 done After you change the mode, Use the following command to run the script The Result is husain-gholooms-macbook:shell husaingholoom$./sc8.sh COUNTER 20 COUNTER 19 COUNTER 18 COUNTER 17 COUNTER husain-gholooms-macbook:shell husaingholoom$ vi sc8.sh Fall 2013 CS4350 Husain Gholoom Page 16

17 Case case variable in pattern1 ) statements ;; pattern2 ) statements ;;... esac Script sc9.sh #!/bin/sh # An example with the case statement # Reads a command from the user and processes it echo "Enter your command (who, list, or cal)" read command case "$command" in who) echo "Running who..." who ;; list) echo "Running ls..." ls ;; cal) echo "Running cal..." cal ;; *) echo "Bad command, your choices are: who, list, or cal" ;; esac exit 0 Fall 2013 CS4350 Husain Gholoom Page 17

18 After you change the mode, Use the following command to run the script husain-gholooms-macbook:shell husaingholoom$./sc9.sh The Result is husain-gholooms-macbook:shell husaingholoom$./sc9.sh Enter your command (who, list, or cal) who Running who... husaingholoom console Sep 7 08:09 husaingholoom ttys000 Sep 7 09:48 husain-gholooms-macbook:shell husaingholoom$./sc9.sh Enter your command (who, list, or cal) list Running ls... sc1.sh sc10.sh sc2.sh sc3.sh sc4.sh sc5.sh sc6.sh sc7.sh sc8.sh sc9.sh husain-gholooms-macbook:shell husaingholoom$./sc9.sh Enter your command (who, list, or cal) cal Running cal... September 2013 Su Mo Tu We Th Fr Sa husain-gholooms-macbook:shell husaingholoom$./sc9.sh Enter your command (who, list, or cal) what Bad command, your choices are: who, list, or cal husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 18

19 Break and Continue break escape from the current for, while, or until loop continue continue at the next iteration of the current for, while, or until loop Script sc10.sh #!/bin/bash x=0 while [ $x -le 5 ] do echo "Before break : $x" x=`expr $x + 1` break echo "After breakn : $x" done echo "While loop finished" After you change the mode, Use the following command to run the script husain-gholooms-macbook:shell husaingholoom$./sc10.sh The Result is Before break : 0 While loop finished husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 19

20 Script sc11.sh #!/bin/bash x=0 while [ $x -le 5 ] do echo "Before continue : $x" x=`expr $x + 1` continue echo "After continue : $x" done echo "While loop finished" After you change the mode, Use the following command to run the script husain-gholooms-macbook:shell husaingholoom$./sc11.sh The Result is Before continue : 0 Before continue : 1 Before continue : 2 Before continue : 3 Before continue : 4 Before continue : 5 While loop finished husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 20

21 The AND list The AND list construct enables you to execute a series of commands, executing the next command only if all the previous commands have succeeded. The syntax is : statement1 && statement2 && statement3 &&... What is the output of the following script #!/bin/sh touch file_one touch file_two if [ -f file_one ] && echo "hello" && [ -f file_two ] && echo " there" then echo "in if" else echo "in else" fi exit 0 What happens if you change the line that contains touch file_two to be rm f file_tw and run the script again? Try the script and you ll get the following result: hello there in if Fall 2013 CS4350 Husain Gholoom Page 21

22 The OR List The OR list construct enables us to execute a series of commands until one succeeds, and then not exe- cute any more. The syntax is as follows: statement1 statement2 statement3... What is the output of the following script #!/bin/sh rm -f file_one if [ -f file_one ] echo "hello" echo " there" then echo "in if" else echo "in else" fi exit 0 This results in the following output: hello in if Fall 2013 CS4350 Husain Gholoom Page 22

23 expr Command Purpose Evaluates arguments as expressions. Syntax expr Expression Description The expr command reads the Expression parameter, evaluates it, and writes the result to standard output. You must apply the following rules to the Expression parameter: Separate each term with blanks. Precede characters special to the shell with a \ (backslash). Quote strings containing blanks or other special characters. The following items describe Expression parameter operators and keywords. Characters that need to be escaped are preceded by a \ (backslash). The items are listed in order of increasing precedence, with equal precedence operators grouped within { } (braces): Fall 2013 CS4350 Husain Gholoom Page 23

24 Item Expression1 \ Expression2 Description Returns Expression1 if it is neither a null value nor a 0 value; otherwise, it returns Expression2. Expression1 \& Expression2 Returns Expression1 if both expressions are neither a null value nor a 0 value; otherwise, it returns a value of 0. Expression1 { =, \>, \>=, \<, \<=,!= } Expression2 Returns the result of an integer comparison if both expressions are integers; otherwise, it returns the result of a string comparison. Expression1 {+, - } Expression2 Adds or subtracts integer-valued arguments. Expression1 { \*, /, % } Expression2 Multiplies, divides, or provides the remainder from the division of integer-valued arguments. Expression1 : Expression2 Compares the string resulting from the evaluation of Expression1 with the regular expression pattern resulting from the evaluation of Expression2. Regular expression syntax is the same as that of the ed command, except that all patterns are anchored to the beginning of the string (that is, only sequences starting at the first character of a string are matched by the regular expression). Therefore, a ^ (caret) is not a special character in this context. Normally the matching operator returns the number of characters matched (0 on failure). If the pattern contains a subexpression, that is: \( Expression \) then a string containing the actual matched characters is returned. Fall 2013 CS4350 Husain Gholoom Page 24

25 Simple Examples #!/bin/bash var1=10 var2=20 var1=$(expr $var1 + 1 ) echo $var1 echo var1=$(expr $var1 \* $var1 ) echo $var1 echo echo $(expr $var1 / 10) echo echo $(expr $var1 % 10) echo expr $var1 = $var2 expr $var1 \< $var2 expr $var1 \!= $var2 exit 0 The Result husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 25

26 (Eval) Arguments as Shell Command in Unix / Linux Eval is a built in linux or unix command. The eval command is used to execute the arguments as a shell command on unix or linux system Eval command comes in handy when you have a unix or linux command stored in a variable and you want to execute that command stored in the string. The following shell script example shows how to use the eval command: Example #!/bin/bash #ls command stored in a variable COMMAND="ls -lrt" #executing the ls command using eval eval $COMMAND exit 0 The Result -rwxr-xr-x@ 1 husaingholoom staff 115 Sep 4 22:24 sc1.sh -rwxr-xr-x 1 husaingholoom staff 327 Sep 7 20:13 sc2.sh -rwxr-xr-x 1 husaingholoom staff 156 Sep 8 12:29 sc4.sh... husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 26

27 The eval command first evaluates the argument and then runs the command stored in the argument. The following example shows how to use the eval command on the unix command line: husain-gholooms-macbook:shell husaingholoom$ eval "rm test.sh" Export export var=value Export the value of var to its global environment so that its child shell can inherit the variable. In terminal export myvar=val1 In a child script echo $myvar Fall 2013 CS4350 Husain Gholoom Page 27

28 Arrays : Defining Array Values: The difference between an array variable and a scalar variable can be explained as follows. Say that you are trying to represent the names of various students as a set of variables. Each of the individual variables is a scalar variable as follows: NAME01="Zara" NAME02="Ryan" NAME03="Gary" NAME04="Ayan" NAME05="Daisy" We can use a single array to store all the above mentioned names. Following is the simplest method of creating an array variable is to assign a value to one of its indices. This is expressed as follows: array_name[index]=value Here array_name is the name of the array, index is the index of the item in the array that you want to set, and value is the value you want to set for that item. As an example, the following commands: NAME[0]="Zara" NAME[1]="Ryan" NAME[2]="Gary" NAME[3]="Ayan" NAME[4]="Daisy" Fall 2013 CS4350 Husain Gholoom Page 28

29 Accessing Array Values: After you have set any array variable, you access it as follows: ${array_name[index]} Here array_name is the name of the array, and index is the index of the value to be accessed. Following is the simplest example: #!/bin/sh NAME[0]="Zara" NAME[1]="Ryan" NAME[2]="Gary" NAME[3]="Ayan" NAME[4]="Daisy" echo "First Index: ${NAME[0]}" echo "Second Index: ${NAME[1]}" This above script will produce following result: $./test.sh First Index: Zara Second Index: Ryan Fall 2013 CS4350 Husain Gholoom Page 29

30 You can access all the items in an array in one of the following ways: echo ${array_name[*]} # show all elements in the array echo ${array_name[@]} echo ${#string[@]} # show array size echo ${NAME[@]:3} # show all elements starting from element 3 echo ${NAME[@]#G*r} # Apply to all elements Matches "Gary" and removes it. echo ${NAME[@]/Zar/XYZ} # Substring Replacement - Replace zar with XYZ - Applied to all elements of the array. Sample Run $./test.sh First Method: Zara Ryan Gary Ayan Daisy Second Method: Zara Ryan Gary Ayan Daisy 5 Fall 2013 CS4350 Husain Gholoom Page 30

31 Ayan Daisy Zara Ryan y Ayan Daisy XYZa Ryan Gary Ayan Daisy What is the output of the following : #!/bin/bash area[11]=23 area[13]=37 area[51]=ufos echo -n "area[11] = " echo ${area[11]} echo -n "area[13] = " echo ${area[13]} echo echo "Contents of area[51] are ${area[51]}." echo -n "area[43] = " echo ${area[43]} echo "(area[43] unassigned)" echo # Sum of two array variables assigned to third area[5]=`expr ${area[11]} + ${area[13]}` echo "area[5] = area[11] + area[13]" echo -n "area[5] = " echo ${area[5]} Fall 2013 CS4350 Husain Gholoom Page 31

32 area[6]=`expr ${area[11]} + ${area[51]}` echo "area[6] = area[11] + area[51]" echo -n "area[6] = " echo ${area[6]} # This fails because adding an integer to a string is not permitted. echo ; echo ; echo # Another array, "area2". # Another way of assigning array variables... # array_name=( XXX YYY ZZZ... ) area2=( zero one two three four ) echo -n "area2[0] = " echo ${area2[0]} # Aha, zero-based indexing (first element of array is [0], not [1]). echo -n "area2[1] = " echo ${area2[1]} array. # [1] is second element of echo; echo; echo Fall 2013 CS4350 Husain Gholoom Page 32

33 # Yet another array, "area3". # Yet another way of assigning array variables... # array_name=([xx]=xxx [yy]=yyy...) area3=([17]=seventeen [24]=twenty-four) echo -n "area3[17] = " echo ${area3[17]} echo -n "area3[24] = " echo ${area3[24]} exit 0 Fall 2013 CS4350 Husain Gholoom Page 33

34 The Result -n area[11] = 23 -n area[13] = 37 Contents of area[51] are UFOs. -n area[43] = (area[43] unassigned) area[5] = area[11] + area[13] -n area[5] = 60 expr: non-numeric argument area[6] = area[11] + area[51] -n area[6] = -n area2[0] = zero -n area2[1] = one -n area3[17] = seventeen -n area3[24] = twenty-four husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 34

35 set The set command sets the parameter variables for the shell. It can be a useful way of using fields in commands that output space-separated values. Suppose you want to use the name of the current month in a shell script. The system provides a date command, which contains the month as a string, but you need to separate it from the other fields. You can do this using a combination of the set command and the $(...) construct to execute the date command and return the result. The date command output has the month string as its second parameter: Example #!/bin/sh echo the date is $(date) set $(date) echo The Day of Week is $1 echo The Month is $2 echo The Day is $3 echo The year is $6 echo The Current Time is $4 echo echo var=$1 Echo $var exit 0 Fall 2013 CS4350 Husain Gholoom Page 35

36 Sample Run husain-gholooms-macbook:shell husaingholoom$./sc16set.sh the date is Sat Sep 14 16:02:23 CDT 2013 The Day of Week is Sat The Month is Sep The Day is 14 The year is 2013 The Current Time is 16:12:15 Sat husain-gholooms-macbook:shell husaingholoom$ Unset NOT "not set" Remove variables from the environment Insert the following code at the end of the previous example unset var echo $var Fall 2013 CS4350 Husain Gholoom Page 36

37 Sample Run husain-gholooms-macbook:shell husaingholoom$./sc16set.sh the date is Sat Sep 14 16:16:35 CDT 2013 The Day of Week is Sat The Month is Sep The Day is 14 The year is 2013 The Current Time is 16:16:35 Sat husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 37

38 Few More Commands The. Command The dot (.) command executes the command in the current shell:../shell_script exec The exec command has two different uses. Its typical use is to replace the current shell with a different program. For example, exec wall Thanks for all the fish in a script will replace the current shell with the wall command. No lines in the script after the exec will be processed, because the shell that was executing the script no longer exists. Fall 2013 CS4350 Husain Gholoom Page 38

39 printf The printf command is available only in more recent shells. X/Open suggests that it should be used in preference to echo for generating formatted output, though few people seem to follow this advice. The syntax is Printf format string parameter1 parameter2... The format string is very similar to that used in C or C++, with some restrictions. Principally, floating point isn t supported, because all arithmetic in the shell is performed as integers. The format string con- sists of any combination of literal characters, escape sequences, and conversion specifiers. All characters in the format string other than % and \ appear literally in the output. The following escape sequences are supported: Escape Sequence Description \ Double quote \\ Backslash character \a Alert (ring the bell or beep) \b Backspace character \c Suppress further output \f Form feed character \n Newline character \r Carriage return \t Tab character \v Vertical tab character \ooo The single character with octal value ooo \xhh The single character with the hexadecimal value HH Fall 2013 CS4350 Husain Gholoom Page 39

40 Description D Output a decimal number. C Output a character. S Output a string. % Output the % character. $ printf %s\n hello hello $ printf %s %d\t%s Hi There 15 people Hi There 15 people In a Script #!/bin/sh printf "%d\n" printf "%d\n" \'A printf "%d\n" "'B" # no argument is specified Sample run Fall 2013 CS4350 Husain Gholoom Page 40

41 Functions in Shell Functions are normally used if a piece of code is repeated at various places in a script. Before you invoke a function, you must define it. A function is invoked by using its name as a command. Another alternative is to create another script file for the block of code and invoke this code by calling the script. Hard to modify the variables in the invoking shell. Take more time to read and execute. Function_name () { command... } Functions are called, triggered, simply by invoking their names. A function call is equivalent to a command. Fall 2013 CS4350 Husain Gholoom Page 41

42 Example #!/bin/bash JUST_A_SECOND=1 funky () { # This is about as simple as functions get. echo "This is a funky function." echo "Now exiting funky function." } # Function declaration must precede call. fun () { # A somewhat more complex function. i=0 REPEATS=3 echo echo "And now the fun really begins." echo sleep $JUST_A_SECOND # Hey, wait a second! while [ $i -lt $REPEATS ] do echo " FUNCTIONS >" echo "< ARE " echo "< FUN >" echo let "i+=1" done } # Now, call the functions. funky fun Fall 2013 CS4350 Husain Gholoom Page 42

43 Sample Run This is a funky function. Now exiting funky function. And now the fun really begins FUNCTIONS > < ARE < FUN > FUNCTIONS > < ARE < FUN > FUNCTIONS > < ARE < FUN > husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 43

44 Passing Parameters to Functions : #!/bin/bash # Functions and parameters DEFAULT=default func2 () { if [ -z "$1" ] then echo "-Parameter #1 is zero length.-" else echo "-Parameter #1 is \"$1\".-" fi # Default param value. # Is parameter #1 zero length? # Or no parameter passed. variable=${1-$default} # What does echo "variable = $variable" #+ parameter substitution show? # # It distinguishes between #+ no param and a null param. if [ "$2" ] then echo "-Parameter #2 is \"$2\".-" fi return 0 } echo echo "Nothing passed." func2 echo # Called with no params Fall 2013 CS4350 Husain Gholoom Page 44

45 echo "Zero-length parameter passed." func2 "" echo echo "One parameter passed." func2 first echo echo "Two parameters passed." func2 first second echo # Called with zero-length param # Called with one param # Called with two params echo "\"\" \"second\" passed." func2 "" second echo # Called with zero-length first parameter # and ASCII string as a second one. exit 0 Fall 2013 CS4350 Husain Gholoom Page 45

46 Sample Run husain-gholooms-macbook:shell husaingholoom$./sc19functions.sh Nothing passed. -Parameter #1 is zero length.- variable = default Zero-length parameter passed. -Parameter #1 is zero length.- variable = One parameter passed. -Parameter #1 is "first".- variable = first Two parameters passed. -Parameter #1 is "first".- variable = first -Parameter #2 is "second".- "" "second" passed. -Parameter #1 is zero length.- variable = -Parameter #2 is "second".- husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 46

47 Function with return values!/bin/bash # Maximum of two integers. E_PARAM_ERR=250 EQUAL=251 # If less than 2 params passed to function. # Return value if both params equal. # Error values out of range of any #+ params that might be fed to the function. max2 () # Returns larger of two numbers. { # Note: numbers compared must be less than 250. if [ -z "$2" ] then return $E_PARAM_ERR fi if [ "$1" -eq "$2" ] then return $EQUAL else if [ "$1" -gt "$2" ] then return $1 else return $2 fi fi } Fall 2013 CS4350 Husain Gholoom Page 47

48 echo This Script finds the largest of two integers echo Enter 2 Integers read var1 var2 #max max2 $var1 $var2 return_val=$? if [ "$return_val" -eq $E_PARAM_ERR ] then echo "Need to pass two parameters to the function." elif [ "$return_val" -eq $EQUAL ] then echo "The two numbers are equal." else echo "The larger of the two numbers is $return_val." fi exit 0 Fall 2013 CS4350 Husain Gholoom Page 48

49 Sample Run husain-gholooms-macbook:shell husaingholoom$./sc20functions.sh This Script find the largest of two integers Enter 2 Integers The larger of the two numbers is 20. husain-gholooms-macbook:shell husaingholoom$./sc20functions.sh This Script find the largest of two integers Enter 2 Integers The two numbers are equal. husain-gholooms-macbook:shell husaingholoom$./sc20functions.sh This Script find the largest of two integers Enter 2 Integers 10 Need to pass two parameters to the function. husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 49

50 Local and Global Variables in Functions #!/bin/bash # Global and local variables inside a function. func () { local loc_var=23 echo echo "\"loc_var\" in function = $loc_var" # Declared as local variable. # Uses the 'local' builtin. global_var=999 # Not declared as local. # Therefore, defaults to global. } echo "\"global_var\" in function = $global_var" func # Now, to see if local variable "loc_var" exists outside the function. echo echo "\"loc_var\" outside function = $loc_var" # $loc_var outside function = # No, $loc_var not visible globally. echo "\"global_var\" outside function = $global_var" # $global_var outside function = 999 # $global_var is visible globally. echo exit 0 Fall 2013 CS4350 Husain Gholoom Page 50

51 Sample Run husain-gholooms-macbook:shell husaingholoom$./sc21functions.sh "loc_var" in function = 23 "global_var" in function = 999 "loc_var" outside function = "global_var" outside function = 999 husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 51

52 Find find path -name pattern option Find a file at the path with the name according to the option Option - type f - type d - newer otherfile - user username - man find find. -name mytest ls -l $(find. -name mytest ) [hag10@zeus ~]$ find. -name grp.sh [hag10@zeus ~]$ ls -ls $(find. -name grp.sh ) Fall 2013 CS4350 Husain Gholoom Page 52

53 Result is./grp.sh 8 -rwx hag10 faculty 99 Sep 18 11:10./grp.sh Filename Expansion Special characters for filename patterns: -? match any single character. file? matches file1 filea but does not match file12 * match any string, including the null string. file* matches anything with a prefix file (file, file12) - [ ] match any one of the enclosed characters. file[12] matches file1 and file2 only file[1 9] matches file1, file2,..., file9 - [^ ] match any except the enclosed characters. Assume the filenames: a1.tex a.c a1.ps ab ab.txt - ls a?.* will be expanded by the shell to - ls a1.tex a1.ps ab.txt Fall 2013 CS4350 Husain Gholoom Page 53

54 Grep grep [options] PATTERN [FILE...] Grep searches the named input FILEs (or standard input if no files are named, or the file name - is given) for lines containing a match to the given PATTERN. By default, grep prints the matching lines. Option - nooption : print the lines that match - -c : print the number of lines that match - -i : ignore case - -l : list the name of files that have the lines - -v : select non-matching lines Script File * greptest * grep ommands #!/bin/sh echo $tmp we who echo echo all grep echo greptest.sh grep -c echo greptest.sh grep -l echo greptest.sh grep -i Echo greptest.sh grep "echo echo" greptest.sh grep -v "echo " greptest.sh Fall 2013 CS4350 Husain Gholoom Page 54

55 Sample Run echo $temp who echo echo 2 grep.sh echo $temp who echo echo who echo echo #!/bin/sh we all husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 55

56 Pattern The. Any single character Not?, but \? Script File * greptest * grep ommands #!/bin/sh echo $tmp we who echo echo grep "e\?ho" greptest.sh grep "e.ho" greptest.sh all Sample Run echo $temp who echo echo echo $temp who echo echo husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 56

57 [ ] and [^ ] A range of characters bread[a-z]bread - breadebread match - bread[abcd]bread no match - bread1bread no match bread[a-za-z]bread - breadbbread match bread[abcd]bread - breadebread no match The * is Kleene star Match zero or more of previous character ba*rgh matches: - brgh - baargh - baaaargh - baaaaaaaargh - baaaaaaaaaaargh Fall 2013 CS4350 Husain Gholoom Page 57

58 The + The \+ is similar, but Match one or more of previous character ba\+rgh again: - brgh - no match! - baargh - baaaargh - baaaaaaaargh - baaaaaaaaaaargh The \( \) \( \) packages characters ( 0 or more ) - bread_\(bacon\)*_bread - bread bread match - bread_bacon_bread match - bread_baconbacon_bread match bread_\(bacon\)\+_bread ( 1 or more ) - bread bread no match! - bread_bacon_bread match - bread_baconbacon_bread match Fall 2013 CS4350 Husain Gholoom Page 58

59 The \{ \} \{n\} The preceding item is matched exactly n times. \{n,\} The preceding item is matched n or more times. \{n,m\} The preceding item is matched at least n times, but not more than m times. The \ \ is the choice character bread_\(a\ b\)_bread - bread_a_bread match - bread_b_bread match bread_\(avocado\ bacon\)_bread - bread_avocado_bread - bread_bacon_bread Fall 2013 CS4350 Husain Gholoom Page 59

60 The $ The end of a line bread$ - breadabread - match - breadbbread - match - bread1 - no match ^ The beginning of a line ^bread - breadabread - match - breadbbread - match - 1bread - no match Fall 2013 CS4350 Husain Gholoom Page 60

61 [: :] Match Pattern Meaning [:alnum:] - alphanumeric [:alpha:] - letter [:cntrl:] - ASCII control [:digit:] - digits [:graph:] - noncontrol, nonspace [:lower:] - lowercase [:print:] - printable [:punct:] - punctuation characters [:space:] - space or tab [:upper:] - uppercase [:xdigit:] - hexadecimal digits Example : Assume that you have the following text in a file called greword.txt Is this a dagger which I see before me, A dagger of the mind, a false creation, Moves like a ghost. Thou sure and firm-set earth. Fall 2013 CS4350 Husain Gholoom Page 61

62 Suppose that you would like to find a line that contains the letter d followed by space. your command will look something like this shell husaingholoom$ grep d[[:space:]] grepword.txt The Result will be Moves like a ghost. Thou sure and firm-set earth. Another Example shell husaingholoom$ grep [[:space:]] grepword.txt or [hag10@zeus ~]$ grep echo[[:blank:]] test2.sh Fall 2013 CS4350 Husain Gholoom Page 62

63 The Result will be A dagger of the mind, a false creation, Or Is this a dagger which I see before me, A dagger of the mind, a false creation, Moves like a ghost. Thou sure and firm-set earth. Or echo "${NAME[0]}" echo "${NAME[1]}" echo "${NAME[2]}" echo "${NAME[*]}" echo ${NAME[@]:3} echo "${#string[@]}" Fall 2013 CS4350 Husain Gholoom Page 63

64 ` ` The output of the execution of a command `ls` is the same as (ls) is the list of the files in the directory $(( )) Evaluate arithmetic expression Similar to expr x=$((10 + 2)) x=$(expr ) x=$((10-2)) x=$(expr 10-2) x=$((10 * 2)) x=$(expr 10 \* 2) x=$((10 / 2)) (10+2) x=$(expr 10 / 2) expr Fall 2013 CS4350 Husain Gholoom Page 64

65 ${ } The range of variable name #!/bin/sh my=10 mymoney=20 echo ${my}money echo $mymoney Sample Run 10money 20 husain-gholooms-macbook:shell husaingholoom$ Fall 2013 CS4350 Husain Gholoom Page 65

66 ${ : } echo ${ } before after after foo foo echo ${foo:-bar} null null bar Set the value of foo to be bar if foo is null ${foo:=bar} null bar bar Set the value of foo to be bar ${foo:?bar} null null foo:bar print foo:bar and set the value of foo to be null ${foo:+bar} foo foo bar returns bar if foo does exist and not null ${ # } The length of a variable's value myvar=12234 echo ${#myvar} 5 Fall 2013 CS4350 Husain Gholoom Page 66

67 ${ % } Remove the smallest matching part from the end foo= echo ${foo%3} echo ${foo%3*} 123 echo ${foo%3?} ${ %% } Remove the largest matching part from the end ${ # } foo= echo ${foo%%3} echo ${foo%%3*} 12 echo ${foo%%3?} Remove the smallest matching part from the beginning foo= echo ${foo#3} echo ${foo#*3} 356 echo ${foo#?3} Fall 2013 CS4350 Husain Gholoom Page 67

68 ${ ## } Remove the largest matching part from the beginning foo= echo ${foo##3} echo ${foo##*3} 56 echo ${foo##?3} Redirect and Pipe Redirect input - cmd < input ( more < file.txt ) Redirect output - cmd > output ( ls l > lsout.txt ) - cmd >> output ( ls l >> lsout2.txt ) Pipe : inter-process - cmd1 cmd2 Fall 2013 CS4350 Husain Gholoom Page 68

69 We can connect processes together using the pipe operator ( ). For example, the following program means run the ps program, sort its output, and save it in the file pssort.out ps sort > pssort.out The sort command will sort the list of words in a textfile into alphbetical order according to the ASCII code set character order. All Other commands man bash Fall 2013 CS4350 Husain Gholoom Page 69

70 Shell Programs Just typing the shell script on the file is a quick and easy way of trying out small code fragments, and is very useful while you are learning or just testing things out. Suppose you have a large number of.sh or C files and wish to examine the files that contain the string echo or printf statements. Rather than search using the grep command for the string in the files and then list the files individually, you could perform the whole operation in an script like this: #!/bin/sh for file in * do if grep -l echo $file then more $file fi done Fall 2013 CS4350 Husain Gholoom Page 70

71 Or, you could perform the whole operation in an interactive script like this: $ for file in * > do > if grep -l echo $file > then > more $file > fi > done Sample Run grp.sh #!/bin/sh for file in * do if grep -l echo $file then more $file fi done test2.sh #!/bin/sh NAME[0]="Zara" NAME[1]="Ryan" echo "${NAME[0]}" echo "${NAME[1]}" echo "${NAME[2]}" echo "${NAME[*]}" echo ${NAME[@]:3} echo "${#string[@]}" exit 0 Fall 2013 CS4350 Husain Gholoom Page 71