Special Bash Variables

$* - This denotes all the parameters passed to the script
at the time of its execution. Which includes $1, $2
and so on.
$0 - Name of the shell script being executed.
$# - Number of arguments specified in the command line.
$? - Exit status of the last command.

Tab size in VI

To set the tab size in vi

:set sts=4

To enable autoindent

:set ai

Exporting and Importing Data into Postgres

To export a postgres database

 pg_dump mydb > db.sql

To reload such a script into a (freshly created) database named newdb:

$ psql -d newdb -f db.sql

VI substitution

#substitution
:%s/fred/joe/igc            : general substitute command
:%s//joe/igc                : Substitute what you last searched for *N*
:%s/~/sue/igc               : Substitute your last replacement string for *N*

If statements in SQL

To have a conditional statement in a SELECT statement, use CASE WHEN…THEN….ELSE.

create view logbook as
        select  "Date",
                "N Number",
                "From","To",
                "Number of Instrument Approaches",
                "Number of Night Landings",
                "Total Flight Duration" - "Night" as "Day",
                "Night",
                "Simulator",
                "Simulated Instrument",
                "Actual Instrument",
                 case when "IsCrossCountry" = true  then "Total Flight Duration"  else 0.0 end as "Cross Country"
         from flights;

Mnemonic for Order of #

Father Charles Goes Down and Ends Battle

Reversed:

Battle Ends and Down Goes Charles’ Father

A simple file IO program in Perl

This program searches the instructions.txt file line by line to and print the lines immediately after the ones matching the Patter /Read.*RegAddr:\ 0×3/.

#!/usr/bin/perl

open INSTR_FILE, "< Instructions.txt" or die "Cannot open instruciton file $!";

print "## Register 3n";

while ($line = <INSTR_FILE>){

        if ($line =~ /Read.*RegAddr: 0x3/){

                $line = <INSTR_FILE>;

                @fields = split /t/,$line;

                print $fields[2],"n";

        }

}

close INSTR_FILE;

Converting Tabs to spaces

To convert tabs to spaces, use “expand” on unix. Use “unexpand” to convert spaces into tabs.