#!/bin/sh
#
# if_sh - mind (mind@metalshell.com)
#
# Basic example on the if structure
#
#       [ http://www.metalshell.com ]

# if list then list [ elif list then list ] ... [ else list ] fi
#
# list: this would be our true/false statement
# then: open's your if structure and every statement within it and 'fi'
#       will be executed if the statement is true.
# list: this is where your commands or statements are placed. This could 
#       also hold other if structures, for, or while structures, 
#       anything; possibilities are endless..
# elif: "else if", if our statement is false elif would be used to test
#       a different statement
# list: this would be our true/false statement
# then: open's your elif structure and pass's all statement's within 
#       it and 'fi'
# list: would be commands, statement's and other structures to pass 
#       within our elif structure
# else: this would be read in if our if structure was false.
# list: would be commands, etc..
#   fi: would finish our if structure

# This half should be used in a if structure.
#
# The below are conditional expressions used to test file attributes 
# and perform string and arithmetic comparisons. All expressions 
# below are true if..
#
#       -a file (file exists)
#       -b file (file exists and is a block special)
#       -c file (file exists and is a character special)
#       -d file (file exists and is a directory)
#       -e file (file exists)
#       -f file (file exists and is a regular file)
#       -g file (file exists and is set-group-id)
#       -h file (file exists and is a symbolic link)
#       -k file (file exists and is sticky)
#       -p file (file exists and is a named pipe)
#       -r file (file exists and is readable)
#       -s file (file exists and has a size greater than zero)
#       -t fd   (file descriptor is open and refers to a terminal)
#       -u file (file exists and is set-user-id)
#       -w file (file exists and is writable)
#       -x file (file exists and is executable)
#       -O file (file exists and is owned by the current user)
#       -G file (file exists and is owned by the current user group)
#       -L file (file exists and is a symbolic link)
#       -S file (file exists and is a socket)
#       -N file (file exists and has been modified since last read)
#
#       file1 -nt file2 (file1 is newer by modification date than file2)
#       file1 -ot file2 (file1 is older by modification date than file2)
#       file1 -ef file2 (file1 and file2 have the same device and inode)
#
#       -o optname (shell option optname is enabled)
#
#       -z string (length of string is zero)
#       -n string (length of string is non-zero)
#
#       string1 == string2 (strings are equal)
#       string1 != string2 (string are not equal)
#       string1 < string2 (string1 sorts before string2)
#       string1 > string2 (string1 sorts after string2)
#
# The below are arithmetic binary operators
#
#       arg1 OP arg2
#       OP:
#               -eq (arg1 is equal to arg2)
#               -ne (arg1 is not equal to arg2)
#               -lt (arg1 is less than arg2)
#               -le (arg1 is less than or equal to arg2)
#               -gt (arg1 is greater than arg2)
#               -ge (arg1 is greater than or equal to arg2)


# in our first example we are going to compare two strings

# define str1 and str2 as a string with: test
str1="test"
str2="test"

# start our first if structure
echo "--- \"if [ \"\$str1\" = \"\$str2\" ]\" example ---"

if [ "$str1" = "$str2" ]
then
        # print success
        echo "$str1 and $str2 match"
fi

# Now we are going to append 'a' to str2 and compare them again
# this time using elif and the else structure's..

# define str2 as a string with: $str2+a (testa)
str2="${str2}a"

# print blank line for spacing
echo

# start our second if structure
echo "--- \"if [ \"\$str1\" = \"\$str2\" ]\" example #2 ---"

if [ "$str1" = "$str2" ]
then
        # print success
        echo "$str1 and $str2 match"

        elif [ "${str1}a" = "$str2" ]
        then
                # print success
                echo "${str1}a and $str2 match"
        else
                # print failure
                echo "Neither $str1 nor $str1a match $str2"
fi

# In our third example we are going to use the if structure in
# a while structure to match a two variables

# define i as a integer of 0
i=0

# define y as a integer of 10
y=10

# print blank line for spacing
echo

# start our third if structure
echo "--- \"if [ \$i -ne \$y ]\" example ---"

while [ 1 -eq 1 ]
do
        # The expr utility evaluates <expression> and writes the 
        # result on standard output.
        # expr <expression>

        # the below would increase $i by 1
        i=`expr $i + 1`
        echo "Number $i of $y"

        if [ $i -eq $y ]
        then
                # print success
                echo "Finished.."

                # break our never-ending while loop
                break
        fi
done