SHELL SCRIPT TUTORIALDoan Quang MinhJune 21,

2012 CTI Cosatech VN

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About this slide

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Shell SCRIPT Tutorial

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Agenda

I. Introduction (5 minutes)

II. Basic syntax (15 minutes)

III. Advanced syntax (25 minutes)

IV. Conclusion (2 minutes)

V. Reference (2 minutes)

VI. Q&A

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I. Introduction

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II. Basic syntax

1. Principle of Script2. Variables3. Branching4. Looping5. Command line Arguments6. Comparisons7. Variable Manipulations

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1. Principle of Script

Defining the Shell Type#!/usr/bin/ksh

Four Types of Lines#!/usr/bin/ksh

# Commentary......

file=/path/file

if [[ $file = $1 ]];then

command

fi

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1. Principle of Script(cont)

Start and End of ScriptThe script starts at the first line and ends either when it encounters an "exit" or the last line. All "#" lines are ignored.

Start and End of Command A command starts with the first word on a line or if

it's the second command on a line with the first word after a";'.

A command ends either at the end of the line or whith a ";". So one can put several commands onto one line:

print -n "Name: "; read name; print "“ Continues commands over more than one line:

grep filename | sort -u | awk '{print $4}' | \

uniq -c >> /longpath/fileII. Basic syntax

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2. Variables

Filling inWhen filling into a variable then one uses just it's

name: state="US" and no blanks. There is no difference between strings and numbers: price=50.

UsingWhen using a variable one needs to put a $ sign

in front of it: print $state $price.

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2. Variables(cont)

ArraysSet and use an array like:

arrname[1]=4 To fill in print ${arraname[1]} To print out ${arrname[*]} Get all elements ${#arrname[*]} Get the number of

elements

DeclarationThere are happily no declarations of variables

needed in ksh. One cannot have decimals only integers.

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3. Branching

“if-then”

if _expr_ then

_cmd(s)_

elif _expr_

_cmd(s)_

else

_cmd(s)_

fi

II. Basic syntax

“case” case _word_ in _pattern1_)

_cmd(s)_ _pattern2_)

_cmd(s)_ *) break ;;esac

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4. Looping

"while"while _expr_ do

_cmd(s)_

done

"for"for _variable_ in _list_

_cmd(s)_

done

II. Basic syntax

"until"until _expr_do

_cmd(s)_done

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5. Command line Argumentsprogram, function or shell $0

argument 1 through 9 $1 .. $9

nth argument ${n}

number of positional parameters $#

every positional parameter $@, $*

decimal value returned by last executed cmd $?

pid of shell $$

pid of last backgrounded command $!

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6. Comparisons

To compare strings one uses "=" for equal and "!=" for not equal.

To compare numbers one uses "-eq" for equal "-ne" for not equal as well as "-gt" for greater than and "-lt" for less than.

if [[ $name = "John" ]];then # commands....

fi if [[ $size -eq 1000 ]];then

# commands.... fi

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6. Comparisons(cont)

With "&&" for "AND" and "||" for "OR" one can combine statements:

if [[ $price -lt 1000 || $name = "Hanna" ]];then # commands....fiif [[ $name = "Fred" && $city = "Denver" ]];then # commands....fi

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7. Variable Manipulations

Removing something from a variable Variables that contain a path can very easily be stripped

of it: ${name##*/} gives you just the filename. Or if one wants the path: ${name%/*}. % takes it away

from the left and # from the right. %% and ## take the longest possibility while % and #

just take the shortest one.

Replacing a variable if it does not yet exist

If we wanted $foo or if not set 4 then: ${foo:-4} but it still remains unset. To change that we use: ${foo:=4}

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7. Variable Manipulations(cont)Exiting and stating something if

variable is not setThis is very important if our program relays on a

certain variable: ${foo:?"foo not set!"}

Just check for the variable${foo:+1} gives one if $foo is set, otherwise

nothing.

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III. Advanced syntax

1. Ksh Regular Expressions

2. Functions

3. Data Redirection

4. Pipes

5. Co-processes

6. Read Input from User and from Files

7. Special Variables

8. Action on Success or Failure of a Command

9. Trivial Calculations

10. Numerical Calculations using "bc"

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1. Ksh Regular Expressions

Ksh has it's own regular expressions. Use an * for any string. So to get all the files ending it .c use *.c. A single character is represented with a ?. So all the files starting with any sign followed bye 44.f can be fetched by: ?44.f.

Especially in ksh there are quantifiers for whole patterns:

?(pattern) matches zero or one times the pattern.*(pattern) matches any time the pattern.+(pattern) matches one or more time the pattern.@(pattern) matches one time the pattern.!(pattern) matches string without the pattern.

Question a string in a variable like: if [[ $var = fo@(?4*67).c ]];then ...

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2. Functions(cont)

DescriptionA function (= procedure) must be defined before it is

called, because ksh is interpreted at run time. It knows all the variables from the calling shell except the commandline arguments. But has it‘s own command line arguments so that one can call it with different values from different places in the script. It has an exit status but cannot return a value like a c funcition can.

Making a FunctionOne can make one in either of the following two ways:

function foo {

# commands...

}

III. Advanced syntax

foo(){ # commands... }

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3. Data Redirection

General

Data redirection is done with the follwoing signs: "> >> < <<". Every program has at least a standardinput, standardoutput and standarderroroutput. All of these can be redirected.

Command Output to File For writing into a new file or for overwriting a file do: command

> file For appending to a file do: command >> file

Standard Error Redirection To redirect the error output of a command do: command 2> file To discard the error alltogether do: command 2>/dev/null To put the error to the same location as the normal output do:

command 2>&1

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3. Data Redirection(cont)

File into CommandIf a program needs a file for input over standard input do:

command < file

Combine Input and Output Redirection command < infile > outfile command < infile > outfile 2>/dev/null

Commands into Program ( Here Document )Every unix command can take it's commands from a text like

listing with:

command <<EOFinput1input2input3EOF

From eof to eof all is feeded into the above mentioned command.

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4. Pipes

For a serial processing of data from one command to the next do:

command1 | command2 | command3 ...e.g. last | awk '{print $1}' | sort -u.

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5. Co-processes

One can have one background process with which one can communicate with read -p and print -p. It is started with command |&.

If one uses: ksh |& then this shell in the background will do everything for us even telnet and so on: print -p "telnet hostname".

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6. Read Input from User and Files

Read in a Variable

From a user we read with: read var. Then the users can type something in. One should first print something like: print -n "Enter your favorite haircolor: ";read var; print "". The -n suppresses the newline sign.

Read into a File Line for Line

To get each line of a file into a variable iteratively do:{ while read myline;do

# process $myline

done } < filename

To catch the output of a pipeline each line at a time in a variable use:

last | sort | {

while read myline;do

# commands

done }III. Advanced syntaxShell SCRIPT Tutorial

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7. Special Variables

program, function or shell $0

argument 1 through 9 $1 .. $9

nth argument ${n}

number of positional parameters $#

every positional parameter $@, $*

decimal value returned by last executed cmd $?

pid of shell $$

pid of last backgrounded command $!

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8. Action (on Success or Failure of a Command)

If one wants to do a thing only if a command succeded then:

command1 && command2.

If the second command has to be performed only if the first one failed, then:

command1 || command2.

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9. Trivial Calculations

Simpe calculations are done with either a "let" in front of it or within (( ... )).

One can increment a variable within the (( )) without a "$": (( a+=1 )) or let a+=1.

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10. Numerical Calculations using "bc"

For bigger calculations one uses "bc" like:

$result=$(print "n=1;for(i=1;i<8;i++)n=i*n;n"|bc)

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IV. Conclusion

Now, I hope this slide gave you some ideas about working with Shell script, especially Korn shell. Please let me know if there’s any mistake or issue in the tutorial. All comments are welcomed.

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V. Reference

1. KSH script BASIC from well.ox.ac.uk

2. Korn Shell (ksh) Programming from bolthole.com

3. Korn shell scripting from IBM

4. KSH - Korn Shell Tutorial from tripod.com

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VI. Q&A

Questions, please ...

Shell SCRIPT Tutorial