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process id of last background process. $$. process id of shell running this script. $. the current shell flags .... BASH Programming Introduction HOWTO: ...

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Shell scriptingPage 1Shell scriptingThursday March 16th 2006Page 2What is Shell?An command language interpreterCommands read and executed from the standard input device(keyboard) or from a (plain text) fileSeveral shells available with Linux including BASH CSH TCSHPage 3hello_world.sh#!/bin/bashecho Hello Worldchmod +x hello_world.shorchmod 755 hello_world.sh./hello_world.shPage 4VariablesSystem variablesUser created variablesNo data typesNo declarationCan contain (almost) anythingPage 5Variables namingName must start with Alphanumeric character or underscorecharacterCasesensitiveNo spaces on either side of the equal signPage 6Variables examplesSTR=Hello WorldDEST_FOLDER=/home/bajazid/data/DEST_F OLDER=/home/bajazid/data/MY_NUMBER=22SUM=$ MY_NUMBER + 1NEW_FILE=test + $SUM #ERROR1_number=3 #ERROR_number1=3Page 7Special variables$?exit status or return code of last command$#number of arguments$@argument 1 thru n with Input Field Separator$*"$1" $2" ... $n$!process id of last background process$$process id of shell running this script$the current shell flagsPage 8readcommandRead variables from command lineecho File name: read FILE_NAMEtouch ${FILE_NAME}.datPage 9Escape charactersUse backslash to escape special charactersExample:echo Hallo BCCSPage 10testcommandUsed to test expression given toifstatementtest expressionor expression ]Three types of expressions File tests String comparisons Numerical comparisonsPage 11Theifstatementif expression1 ]thenecho expression1 is trueelif expression2 ]thenecho expression2 is trueelseecho all other casesfiPage 12File teststest option fileor option file ]Exampleif d /Home/bccs/bajazid/bin ] ; thenPATH="$PATH:/Home/bccs/bajazid/bi nfiPage 13File tests optionsd fileTrue if file exists and is a directory.e fileTrue if file exists.f fileTrue if file exists and is a regular file.h fileTrue if file exists and is a symbolic link.r fileTrue if file exists and is readable.s fileTrue if file exists and has a size gr ...

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