Tutorial by Examples: d

This section describes some basic DDL (="Data Definition Language") commands to create a database, a table within a database, a view and finally a stored procedure. Create Database The following SQL command creates a new database Northwind on the current server, using pathC:\Program Fi...

You must create your own database, and not use write to any of the existing databases. This is likely to be one of the very first things to do after getting connected the first time. CREATE DATABASE my_db; USE my_db; CREATE TABLE some_table; INSERT INTO some_table ...; You can reference your...

Bashdb is a utility that is similar to gdb, in that you can do things like set breakpoints at a line or at a function, print content of variables, you can restart script execution and more. You can normally install it via your package manager, for example on Fedora: sudo dnf install bashdb Or ...

The following databases exist for MySQL's use. You may read (SELECT) them, but you must not write (INSERT/UPDATE/DELETE) the tables in them. (There are a few exceptions.) mysql -- repository for GRANT info and some other things. information_schema -- The tables here are 'virtual' in the sense ...

On Julia, you can define more than one method for each function. Suppose we define three methods of the same function: foo(x) = 1 foo(x::Number) = 2 foo(x::Int) = 3 When deciding what method to use (called dispatch), Julia chooses the more specific method that matches the types of the argument...

You can list all files ignored by git in current directory with command: git status --ignored So if we have repository structure like this: .git .gitignore ./example_1 ./dir/example_2 ./example_2 ...and .gitignore file containing: example_2 ...than result of the command will be: $ g...

ORDER BY x ASC -- same as default ORDER BY x DESC -- highest to lowest ORDER BY lastname, firstname -- typical name sorting; using two columns ORDER BY submit_date DESC -- latest first ORDER BY submit_date DESC, id ASC -- latest first, but fully specifying order. ASC = ASCENDING, DESC ...

When the shell performs parameter expansion, command substitution, variable or arithmetic expansion, it scans for word boundaries in the result. If any word boundary is found, then the result is split into multiple words at that position. The word boundary is defined by a shell variable IFS (Interna...

See what, when and why if you don't know about the affiliation of IFS to word splitting let's set the IFS to space character only: set -x var='I am a multiline string' IFS=' ' fun() { echo "-$1-" echo "*$2*" echo ".$3." } fun $var This time wo...

$ a='I am a string with spaces' $ [ $a = $a ] || echo "didn't match" bash: [: too many arguments didn't match [ $a = $a ] was interpreted as [ I am a string with spaces = I am a string with spaces ]. [ is the test command for which I am a string with spaces is not a single argument...

There are some cases where word splitting can be useful: Filling up array: arr=($(grep -o '[0-9]\+' file)) This will fill up arr with all numeric values found in file Looping through space separated words: words='foo bar baz' for w in $words;do echo "W: $w" done Output...

readarray -t arr <file Or with a loop: arr=() while IFS= read -r line; do arr+=("$line") done <file

var='line 1 line 2 line3' readarray -t arr <<< "$var" or with a loop: arr=() while IFS= read -r line; do arr+=("$line") done <<< "$var"

while IFS= read -r line;do echo "**$line**" done < <(ping google.com) or with a pipe: ping google.com | while IFS= read -r line;do echo "**$line**" done

Let's assume that the field separator is : (colon) in the file file. while IFS= read -d : -r field || [ -n "$field" ]; do echo "$field" done <file For a content: first : se con d: Thi rd: Fourth The output is: **first ** ** se con d** ** Thi ...

Let's assume that the field separator is : var='line: 1 line: 2 line3' while IFS= read -d : -r field || [ -n "$field" ]; do echo "-$field-" done <<< "$var" Output: -line- - 1 line- - 2 line3 -

Let's assume that the field separator is : arr=() while IFS= read -d : -r field || [ -n "$field" ]; do arr+=("$field") done <file

Let's assume that the field separator is : var='1:2:3:4: newline' arr=() while IFS= read -d : -r field || [ -n "$field" ]; do arr+=("$field") done <<< "$var" echo "${arr[4]}" Output: newline

Let's assume that the field separator is : while IFS= read -d : -r field || [ -n "$field" ];do echo "**$field**" done < <(ping google.com) Or with a pipe: ping google.com | while IFS= read -d : -r field || [ -n "$field" ];do echo "**$field**&q...

a='I am a simple string with digits 1234' pat='(.*) ([0-9]+)' [[ "$a" =~ $pat ]] echo "${BASH_REMATCH[0]}" echo "${BASH_REMATCH[1]}" echo "${BASH_REMATCH[2]}" Output: I am a simple string with digits 1234 I am a simple string with digits 1234