Ksh Scripting

ksh Scripting Contents Principle of Script Variables Branching Looping Command line Arguments Comparisons Variable Manipulations ksh Regular Expressions Functions Data Redirection Pipes Co-processes Read Input from User and from Files Special Variables Action on Success or Failure of a Command Trivial Calculations Numerical Calculations using "bc" "grep" "sed" "awk" "perl"

Principle of Script Defining the Shell Type To make a ksh script (which is a ksh program) crate a new file with a starting line like: #!/usr/bin/ksh It is important that the path to the ksh is proper and that the line doesn’t not have more than 32 characters. The shell from which you are starting the script will find this line and hand the whole script over to ksh. Without this line the script would be interpreted by the same typ of shell as the one, from which it was started. But since the syntax is different for all shells, it is necessary to define the shell with that line.

Four Types of Lines A script has four types of lines: The shell defining line at the top, empty lines, commentary lines starting with a # and command lines. See the following top of a script as an example for these types of lines: #!/usr/bin/ksh # Commentary...... file=/path/file if [[ $file = $1 ]];then command fi

Start and End of Script The 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 with a ";". So one can put several commands onto one line: print -n "Name: "; read name; print ""

One can continue commands over more than one line with a "\" immediately followed by a newline sign which is made be the return key: grep filename | sort -u | awk '{print $4}' | \ uniq -c >> /longpath/file

Name and Permissions of Script File

The script must not have a name which is identical to a unix command: So the script must NOT be called "test"! After saving the file give it the execute permissions with: chmod 700 filename.

Variables Filling in When filling into a variable then one uses just its name: state="US" and no blanks. There is no difference between strings and numbers: price=50.

Using When using a variable one needs to put a $ sign in front of it: print $state $price.

Arrays Set 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

Declaration There are happily no declarations of variables needed in ksh. One cannot have decimals only integers.

Branching

if then fi if [[ $value -eq 7 ]];then print "$value is 7" fi or: if [[ $value -eq 7 ]] then print "$value is 7" fi or: if [[ $value -eq 7 ]];then print "$value is 7";fi

if then else fi

if [[ $name = "John" ]];then print "Your welcome, ${name}." else print "Good bye, ${name}!" fi

if then elif then else fi

if [[ $name = "John" ]];then print "Your welcome, ${name}." elif [[ $name = "Hanna" ]];then print "Hello, ${name}, who are you?" else print "Good bye, ${name}!" fi

case esac

case $var in john|fred) print $invitation;; martin) print $declination;; *) print "Wrong name...";; esac

Looping

while do done while [[ $count -gt 0 ]];do print "\$count is $count" (( count -= 1 )) Done

until do done

until [[ $answer = "yes" ]];do print -n "Please enter \"yes\": " read answer print "" done

for var in list do done

for foo in $(ls);do if [[ -d $foo ]];then print "$foo is a directory" else print "$foo is not a directory" fi done

continue...break One can skip the rest of a loop and directly go to the next iteration with: "continue". while read line do if [[ $line = *.gz ]];then continue else print $line fi done

One can also prematurely leave a loop with: "break". while read line;do if [[ $line = *!(.c) ]];then break else print $line fi done

Command Line Arguments (Officially they are called "positional parameters")

The number of command line arguments is stored in $# so one can check for arguments with: if [[ $# -eq 0 ]];then print "No Arguments" exit fi

The single Arguments are stored in $1, ....$n and all are in $* as one string. The arguments cannot directly be modified but one can reset the whole command line for another part of the program. If we need a first argument $first for the rest of the program we do: if [[ $1 != $first ]];then set $first $* fi

One can iterate over the command line arguments with the help of the shift command. Shift indirectly removes the first argument. until [[ $# -qe 0 ]];do # commands .... shift done

One can also iterate with the “for” loop, the default with for is $*: for arg;do print $arg done

The program name is stored in $0 but it contains the path also!

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

With "&&" for "AND" and "||" for "OR" one can combine statements: if [[ $price -lt 1000 || $name = "Hanna" ]];then # commands.... fi if [[ $name = "Fred" && $city = "Denver" ]];then # commands.... fi

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

Exiting and stating something if variable is not set This is very important if our program relays on a certain vaiable: ${foo:?"foo not set!"}

Just check for the variable ${foo:+1} gives one if $foo is set, otherwise nothing.

ksh Regular Expressions Ksh has its 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. So one can question a string in a variable like: if [[ $var = fo@(?4*67).c ]];then ...

Functions Description A 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 command line 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 function can.

Making a Function One can make one in either of the following two ways: function foo { # commands... } foo(){ # commands... }

Calling the Function To call it just put it's name in the script: foo. To give it arguments do: foo arg1 arg2 ... The arguments are there in the form of $1...$n and $* for all at once like in the main code. And the main $1 is not influenced bye the $1 of a particular function.

Return

The return statement exits the function immediately with the specified return value as an exit status.

Data Redirection General Data redirection is done with the following 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 altogether do: command 2>/dev/null To put the error to the same location as the normal output do: command 2>&1

File into Command If 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 <<EOF input1 input2 input3 EOF From eof to eof all is fed into the above mentioned command.

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.

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".

Read Input from User and from 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 }

Special Variables $# Number of arguments on command line. $? Exit status of last command. $$ Process id of current program. $! Process id of last background job or background function. $0 Program name including the path if started from another directory. $1..n Command line arguments, each at a time. $* All command line arguments in one string.

Action on Success or on Failure of a Command If one wants to do a thing only if a command succeeded then: command1 && command2. If the second command has to be performed only if the first one failed, then: command1 || command2.

Trivial Calculations Simple 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.

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)

"grep" Search for the occurrence of a pattern in a file: grep 'pattern' file. If one just wants to know how often something occurs in a file, then: grep -c 'pattern file. This can be used in a script like: if [[ $(grep -c 'pattern' file) != 0 ]];then ......;fi. The condition is fulfilled if the pattern was found.

"sed" Sed means stream line editor. It searches like grep, but is then able to replace the found pattern. If you want to change all occurrences of "poor" with "rich", do: sed -e 's/poor/rich/g' filename. Or what is often seen in software packages, that have to be compiled after getting a proper configuration, is a whole file stuffed with replacements patterns like: /@foo@/s;;king;g. This file with innumerable lines like that has to be given to sed with: sed -f sedscript filename. It then processes each line from file with all the sed commands in the sed script. (Of course sed can do much more:-))

"awk" Awk can find and process a found line with several tools: It can branch, loop, read from files and also print out to files or to the screen, and it can do arithmetics. For example: We have a file with lines like: Fred 300 45 70 but hundreds of them. But some lines have a "#" as the first sign of them and we have to omit these ones for both, processing and output. And we want to have lines as output like: 415 Fred where 415 is the sum of 300, 45 and 70. Then we call on awk: awk '$1 !~ /^#/ && $0 ~ /[^ ]/ {print $2+$3+$4,"\t",$1}' filename. This ignores lines with a "#" at the beginning of the first field and also blank lines. It then prints the desired sum and the $1 ist only printed after a tab. This is the most trivial use of awk only.

"perl"

Perl is a much richer programming language then ksh, but still one can do perl commands from within a ksh script. This might touch Randal, but it's true. Let's say you want to remove all ^M from a file, then take perl for one line in your ksh script: perl -i -ep 's/\015//g' filename. Perl can do an infinite amount of things in many different ways. For anything bigger, use perl instead of a shell script.