LINUX:Control statements in shell programming

LINUX:Control statements in shell programming

• 1.
  CONTROL STATEMENTS IN SHELL PROGRAMMING BHATVIJETHA
• 2.
  CONTROL STATEMENTS If If(conditional_command) format1 then <commands> fi If(conditional_command)format2 then <commands> else <commands> fi
• 3.
  if (conditional_command) format3 then <commands> elif(conditional_command) then <commands> .. else <commands> fi
• 4.
  • If thespecified <conditional_command> is executed successfully then the commands in between then and else will be executed. • Otherwise if the specified <conditional_command>is not executed successfully then the commands in between else and fi will be executed.
• 5.
  Test command • Thiscommand is used to test the validity of its arguments . And mostly this command is used in conditional _commands. • This test command returns an exit status 0 if test succeeds and 1 false if the test fails. General format is, Test expression String comparision : general format is , test operation Where the operation can be, String 1=string2 - compares two strings ; returns true if both are equal else return false String1!=string2 - compares two strings; strings ; returns true if both are equal else return false -z string - checks whether the specified string is of zero or not, returns true if the string is null, else return false -n string - checks whether the specified string is of zero or not,returns true if the string is null,else return false
• 6.
  Numerical comparision operations meaning -eqReturns true if number1 is equal to number2..else false. -ne Returns true if number1 is not equal to number2 else returns false. -gt Returns true if number1 is greater than number2 else returns false. -lt Returns true if number1 is less than number2 else returns false. -ge Returns true if number1 is less than number2 else returns false. -le Returns true if number1 is less than or equal to number2 else returns false. General format is, Test number1 operator number2
• 7.
  Case statement This isa multi- branch control statement. General format is, Case value is, Pattern1) <commands>;; Pattern2)<commands>;; .. patternN)<commands>;; Esac
• 8.
  • This statementcompares the value to the patterns from the top to bottom , and performs the commands associated with the matching pattern. • The commands for each pattern must be terminated by double semicolon.
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  End of presentation