shell scripting

hmehta.scs@dauniv;ac.inSchool of Computer Science and Information Technology

Devi Ahilya Vishwavidyalaya

Shell Scripting

hmehta.scs@dauniv.ac.in

SCSITDAVV

Applications of Shell Scripts

Task 1: There is a text file having data in columns. Store a particular column in a different file.

Task 2: Sort a file. Task 3: Apply sorting in the output file of Task 1. Task 4: Store only unique data in the output file.

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Task 5: Store the data which satisfy the given condition. Task 6: Transfer the file to the client’s machine for the further

processing. Task 7: Determine whether the executed program completed

successfully or not. Task 8: In case of failure produce the signal for error.

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Solution

#!/bin/kshHOST=‘ftp.myserverid.mydomain’

USER=‘MyUserid’

PASSWD=‘MyPassword‘

FILE=“filename”OUTFILE=“newfile”MAILINGLIST=“supportmail.lst”LOG=“logfile”cut –c5,6 $FILE| sort| uniq > $OUTFILE

awk '{if ($2 > 30) print $1}‘ $OUTFILE

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Solutionftp -n $HOST > /tmp/ftp.worked 2> /tmp/ftp.failed <<END_SCRIPT

user $USER

pass $PASSWD

put $FILE

END_SCRIPT

EXITSTATUS=$?

if [ $EXITSTATUS != "0" ]

for PEOPLE in `cat $MAILINGLIST`

/usr/bin/mailx –s “a process is failed” $PEOPLE

[$? –ne 0] && echo “$PEOPLE mailx failed” >>$LOG

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Requirement: Need to execute a program on a particular time (System time).

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Requirement: Logging the information about the execution of a job.

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Requirement: Need to execute a program on a particular time (System time) but after successful completion of a job.

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Requirement: Need to execute a program on a particular time (System time) but after successful completion of a job. Also check for the existence of a particular file.

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Requirement: Need to know that whether a particular job completed successfully or not.

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Requirement: Sending Mail/ SMS in case of error in the execution.

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Requirement: Working like database on the text files.

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Requirement: Fetching columns/ rows from a file, counting the records, filtering the data, sorting the data, Pattern matching/ replacing.

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Requirement: Handling CSV Files.

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Requirement: Periodic Monitoring the system activities like disk space utilization etc.

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Requirement: Sending / Receiving data to / from Remote location/computer.

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Requirement: Checking for the existence and permission for a file.

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Requirement: System administrators, for automating many aspects of computer maintenance, user account creation etc.

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Requirement: Application package installation tools.

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Requirement: Application startup scripts, especially unattended applications.

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Requirement: Data Synchronization.

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Requirement: Interface between Os and other tools/language like Java, Oracle, FTP.

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Requirement: Log Rotation.

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Requirement: Purging of old files and data.

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Requirement: Removing blank files and File comparison.

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The Shell & Shell Script

A shell is a command interpreter turns the input text in to actions. Bourne Shell Bourne Again Shell Korn Shell C Shell etc. .. .. ..

A Shell Script is a logical sequence of commands.

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The Anatomy of a Command

grep –i localhost /etc/hosts

Command Option Arguments

Options Change the behavior of a command

Arguments control what the command act upon

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Running the Shell Script

Type the name of a program and some command line options. The shell reads this line, finds the program and runs it, feeding it the

specified options. The shell establishes 3 I/O channels:

Standard Input Standard Output Standard Error

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The Shebang (#!)

The Shebang is a special comment. It specifies which shell to use to execute this shell script. If no “#!” found, the current shell will be used to run the script. Example

#!/bin/ksh

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Two ways to execute the Shell

Set the permission attributes as a executable file then execute it like a command.

Invoke the shell explicitly.

sh backup8pm.sh

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Debugging the Shell Script

Running a script in debug mode will print each line of shell script before it executes.

Enable debug mode after adding the –v after shell interpreter’s name in Shebang.

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Advantages

Writing a shell script is much quicker than writing the equivalent code in other programming or scripting languages.

Shell scripts have no compilation step, so the script can be executed quickly while debugging.

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Disadvantages

One significant disadvantage of using shell scripts is that they can run slowly due to the need to create potentially many new sub-processes for each of the many commands executed.

Simple sh scripts can be quite compatible with the extremely diverse range of Unix but more complex shell scripts can fail because of the many subtle differences between shells.

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Programs and Standard I/O

ProgramProgramStandard Input

(STDIN)

Standard Output

(STDOUT)

Standard Error

(STDERR)

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Overwriting the Standard I/O Device

Input/ Output Redirection

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• A pipe is a holder for a stream of data.

• A pipe can be used to hold the output of one program and feed it to the input of another.

prog1prog1 prog2prog2STDOUT STDIN

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Regular Expression

Regular Expressions provide a concise and flexible means for identifying text of interest.

Examples:

[abc] matches a single a b or c [a-z] matches any of abcdef…xyz

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Regular Expression

Examples: .at matches any three-character string ending with "at", including

"hat", "cat", and "bat". [hc]at matches "hat" and "cat". [^b]at matches all strings matched by .at except "bat". ^[hc]at matches "hat" and "cat", but only at the beginning of the

string or line. [hc]at$ matches "hat" and "cat", but only at the end of the string or

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Regular Expression

Examples: .at matches any three-character string ending with "at", including

"hat", "cat", and "bat". [hc]at matches "hat" and "cat". [^b]at matches all strings matched by .at except "bat". ^[hc]at matches "hat" and "cat", but only at the beginning of the

string or line. [hc]at$ matches "hat" and "cat", but only at the end of the string or

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Regular Expression

Used by grep “Get Regular Expression and Print” – search files

line by line sed Simple Editing tool, right from the command line awk Scripting language, executes “program” on

matching lines

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Important Commands (UNIX)

touch: create a new file / update timestamp of existing file. grep: search for a specified string or pattern chmod/ chown/ chgrp: Change permissions / ownership /

group on a file du/ df: Display hard disk information. find:find a file sort: sort a file into alphanumeric order (by lines.) sed: Invoke the stream editor. tr: Translate characters. awk: Invoke the awk scripting language. split: Split up a file into smaller chunks.

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Important Commands (UNIX)

at: Run a command / script at a specified time and date. Cut: cut specified field(s)/ character(s) from lines in file(s) more, less, and pg: page through a file head/ tail: display the start/ end of a file cmp: compare two files and list where differences occur (T/B) diff : compare the two files and display the differences (T) wc: display word (or character or line) count for file(s) mail/ mailx/ Mail: simple email utility available on Unix systems. paste: The paste command allows two files to be combined

side-by-side.

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Important Commands (WinNT)

AT: Schedule a command to run at a later time ATTRIB: Change file attributes CACLS: Change file permissions . CleanMgr: Automated cleanup of Temp files, recycle bin COMP: Compare the contents of two files or sets of files FC: Compare two files FDISK: Disk Format and partition FIND: Search for a text string in a file Magnify: Display windows magnification MAPISEND: Send email from the command line MEM: Display memory usage

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Important Commands (WinNT)

MORE: Display output, one screen at a time MSG: Send a message NET: Manage network resources PERFMON: Performance Monitor QGREP: Search file(s) for lines that match a given pattern. SCHTASKS: Create or Edit Scheduled Tasks SCLIST: Display NT Services SORT: Sort input TOUCH: Change file timestamps USRSTAT List domain usernames and last login

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Book for UNIX

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Book for WinNT

hmehta.scs@dauniv;ac.inSchool of Computer Science and Information Technology

Devi Ahilya Vishwavidyalaya

Thank You

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