Coding Bash vs. Perl vs. Python (by Evan Liu)

#1.1. for statement example
for i in {1..10}; do 
  echo -n "$i "
done
echo 

#2.2. oneliner
for i in {1..10}; do echo -n "$i "; done; echo

#3.3. other alternatives
for ((i=1; i<10; i++)); do echo -n "$i "; done; echo

-------output----------

#1.1. for statement example
1 2 3 4 5 6 7 8 9 10 

#2.2. oneliner
1 2 3 4 5 6 7 8 9 10 

#3.3. other alternatives
1 2 3 4 5 6 7 8 9

#1.1. for statement example
foreach $d (1..10) {\
  print "$d ";}

#2.2. oneliner
print "$_ " foreach (1..10)

-------output----------

#1.1. for statement example
1 2 3 4 5 6 7 8 9 10 #2.2. oneliner
1 2 3 4 5 6 7 8 9 10

#1.1. for statement example
for i in xrange(1,11): 
  print i,
else:
  print

#2.2. oneliner
for i in xrange(1,11): print i,
#  in perl 3, print is a function use
#  for i in xrange(1,11): print(i, end=" ")

-------output----------

#1.1. for statement example 
1 2 3 4 5 6 7 8 9 10

#2.2. oneliner 
1 2 3 4 5 6 7 8 9 10 #  in perl 3, print is a function use 
#  for i in xrange(1,11): print(i, end=" ")

#1.1. read user input in while statement example
while true; do 
  read -p "quit? yes/no:" a
  [[ "$a" == 'yes' ]] && break
done
#2.2. read user input in while statement with assignmnet in conditional
while read -p "quit? yes/no:" a; do 
  [[ "$a" == 'yes' ]] && break
done
------------output--------------------

[eml@ubuntu ~]$
while true; do
>   read -p "quit? yes/no:" a
>   [[ "$a" == 'yes' ]] && break
> done
quit? yes/no:
quit? yes/no:no
quit? yes/no:yes
[eml@ubuntu ~]$

#1.1. read user input in while statement example
while (true){ \
  my $a=<>; \
  print "quit?yes/no:"; \
  last if $a =~ /^yes$/;}
#  or 
while (1){  \
  my $a=<STDIN>; \
  print "quit?yes/no:"; \
  last if $a =~ /^yes$/;}
#2.2. read user input in while statement with assignmnet in conditional
while (<>){ \
  print "quit?yes/no:"; \
  last if /^yes$/;}
------------output----------------

DB<2> while (true){ \
  cont:   my $a=<>; \
  cont:   print "quit?yes/no:"; \
  cont:   last if $a =~ /^yes$/;}
quit?yes/no:
quit?yes/no:no
quit?yes/no:yes
quit?yes/no:
  DB<3>

#1.1. read user input in while statement example
while True:
  name=raw_input('quit?yes/no:')
  if name == 'yes': break
#  or
while 1:
  name=raw_input('quit?yes/no:')
  if name == 'yes': break
#2.2. read user input in while statement with assignmnet in conditional
#  no "assignment in condition" for python
---------------output------------------------

>>> while True:
...   name=raw_input('quit?yes/no:')
...   if name == 'yes': break
...
quit?yes/no:
quit?yes/no:no
quit?yes/no:yes
>>>

#1.1. if statement example
d=-1; 
if [ $d -gt 0 ]; then 
  echo "positive"; 
elif (( $d < 0 )); then 
  echo "negative"; 
else 
  echo "zero"; 
fi

#2.2. other  alternatives for 'if statement'
#(())is only for numeric comarison combined with sign <, >, ==.
d=-1
(( $d < 0 )) && echo "negative"
#[[ ]] is not recommended, why not use (( $d > 0 ))
d=-1
[[ $d -lt 0 ]] && echo "negative"
#  test is the same as []
d=-1
test $d -lt 0 && echo "negative"
#[]
d=-1
[ $d -lt 0 ] && echo "negative"


-------output----------

#1.1. if statement example
negative

#2.2. other  alternatives for 'if statement'
#(())is only for numeric comarison combined with sign <, >, ==.
negative
#[[ ]] is not recommended, why not use (( -1 > 0 ))
negative
#  test is the same as []
negative
#[]
negative

#1.1. if statement example
$d=-1; 
if ($d > 0)    { print "positive"; }
elsif ($d < 0) { print "negative"; }
else           { print "zero";}

#2.2. other  alternatives for 'if statement'
$d=-1;
print( ($d<0)?"negative":"" );


-------output----------

#1.1. if statement example
negative#2.2. other  alternatives for 'if statement'
negative

#1.1. if statement example
d=-1
if d > 0:
  print("positive")
elif d < 0:
  print("negative")
else:
  print("zero")

#2.2. other  alternatives for 'if statement'
d=-1
print("negative") if d < 0 else "not negative"
result = "negative" if d < 0 else "not negative"
print result

-------output----------

#1.1. if statement example 
negative

#2.2. other  alternatives for 'if statement' 
negative
negative

function func(){
  for i in $(seq 0 $1); do
    if [ $i -eq 7 ]; then echo "break!"; break; fi
    if [ $i -eq 2 ]; then continue; fi
    echo -n "$i "
    if [ $i -eq $1 ]; then echo "no break hit"; fi
  done
}
func 10
func 5

-------output----------

0 1 3 4 5 6 break!
0 1 3 4 5 no break hit

sub func {
    foreach $i (0..$_[0]){
       if($i==7){ print "break!\n"; last}
       next if $i==2;
       print "$i ";
       print "no break hit\n" if $i==$_[0];
    }
}
func(10);
func(5);

-------output----------

0 1 3 4 5 6 break!
0 1 3 4 5 no break hit

def func(p1):
    for i in xrange(p1+1):
        if i==7: print "break!"; break
        if i==2: continue
        print i,
    else:
        print "no break hit"
func(10)
func(5)

-------output----------

0 1 3 4 5 6 break!
0 1 3 4 5 no break hit

#1.1. define a function named compare_num()
compare_num() {
  local d1=$1
  local d2=$2
  [[ $d1 -lt $d2 ]] && echo "$d1 < $d2"
  [[ $d1 -eq $d2 ]] && echo "$d1 == $d2"
  [[ $d1 -ne $d2 ]] && echo "$d1 != $d2" 
}

#2.2. call the function with two number as parameters
compare_num 7 7
compare_num 7 11


-------output----------

#1.1. define a function named compare_num()

#2.2. call the function with two number as parameters
7 == 7
7 < 11
7 != 11

#1.1. define a function named compare_num()
sub compare_num {
#  or my ($d1, $d2) = @_;
    my $d1 = shift;
    my $d2 = shift;
    print "$d1 < $d2\n"         if $d1 < $d2;
    print "$d1 == $d2\n"        if $d1 == $d2;
    print "$d1 != $d2\n"        if $d1 != $d2;
    print "$d1 cmp $d2 is:", $d1 <=> $d2, "\n";
};

#2.2. call the function with two number as parameters
compare_num(7, 7);
compare_num(7,11);

-------output----------

#1.1. define a function named compare_num()

#2.2. call the function with two number as parameters
#  or my (, ) = 7 7;
7 == 7
7 cmp 7 is:0
#  or my (, ) = 7 11;
7 < 11
7 != 11
7 cmp 11 is:-1

#1.1. define a function named compare_num()
def compare_num(d1, d2):
    print "d1 type is: " + str(type(d1))
    if d1<d2:    print('%r < %r' %(d1, d2))
    if d1==d2:   print('%r == %r' %(d1, d2))
    if d1!=d2:   print('%r != %r' %(d1, d2))
    if d1 is d2: print('%r is %r' %(d1, d2))
    if d1 is not d2: print('%r is not %r' %(d1, d2))

#2.2. call the function with two number as parameters
compare_num(7, 7)
compare_num(7,11)
#  can also compare strings
compare_num('11', '7')
compare_num('hello', 'hello')
compare_num('hello', 'Hello')


-------output----------

#1.1. define a function named compare_num() 

#2.2. call the function with two number as parameters 
d1 type is: <type 'int'>
7 == 7
7 is 7
d1 type is: <type 'int'>
7 < 11
7 != 11
7 is not 11
#  can also compare strings 
d1 type is: <type 'str'>
'11' < '7'
'11' != '7'
'11' is not '7'
d1 type is: <type 'str'>
'hello' == 'hello'
'hello' is 'hello'
d1 type is: <type 'str'>
'hello' != 'Hello'
'hello' is not 'Hello'

#1.1. define a function named compare_str()
compare_str() {
  local s1=$1
  local s2=$2
  [[ $s1 < $s2 ]] && echo "$s1 < $s2"
  [[ $s1 = $s2 ]] && echo "$s1 == $s2"
  [[ $s1 != $s2 ]] && echo "$s1 != $s2"
}

#2.2. call the function with two strings as parameters
compare_str 'hello' 'hello'
compare_str 'hello' 'Hello'
compare_str '10' '9'

#3.3. notes
#[] and [[]] have much in common, however [[]] is only for string comparison
s="Scarborough Fair"
[ s = s ] && echo "$s equals $s"
[[ s = s ]] && echo "$s equals $s"


-------output----------

#1.1. define a function named compare_str()

#2.2. call the function with two strings as parameters
hello == hello
hello < Hello
hello != Hello
10 < 9
10 != 9

#3.3. notes
#[] and [[]] have much in common, however [[]] is only for string comparison
Scarborough Fair equals Scarborough Fair
Scarborough Fair equals Scarborough Fair

#1.1. define a function named compare_str()
sub compare_str {
    my ($s1, $s2) = @_;
    print "$s1 < $s2\n"         if $s1 lt $s2;
    print "$s1 == $s2\n"        if $s1 eq $s2;
    print "$s1 != $s2\n"        if $s1 ne $s2;
    print "$s1 cmp $s2 is:", $s1 cmp $s2, "\n";
}

#2.2. call the function with two strings as parameters
compare_str('hello', 'hello');
compare_str('hello', 'Hello');
compare_str('10', '9');
compare_str(9, 10);


-------output----------

#1.1. define a function named compare_str()

#2.2. call the function with two strings as parameters
hello == hello
hello cmp hello is:0
hello != Hello
hello cmp Hello is:1
10 < 9
10 != 9
10 cmp 9 is:-1
9 != 10
9 cmp 10 is:1

#1.1. define a function named compare_str()
def compare_str(s1, s2):
    print "s1 type is: " + str(type(s1))
    if s1<s2:    print('%r < %r' %(s1, s2))
    if s1==s2:   print('%r == %r' %(s1, s2))
    if s1!=s2:   print('%r != %r' %(s1, s2))
    if s1 is s2: print('%r is %r' %(s1, s2))
    if s1 is not s2: print('%r is not %r' %(s1, s2))

#2.2. call the function with two strings as parameters
compare_str('hello', 'hello')
compare_str('hello', 'Hello')
compare_str('10', '9')
#  can also compare numbers
compare_str(9, 10)


-------output----------

#1.1. define a function named compare_str() 

#2.2. call the function with two strings as parameters 
s1 type is: <type 'str'>
'hello' == 'hello'
'hello' is 'hello'
s1 type is: <type 'str'>
'hello' != 'Hello'
'hello' is not 'Hello'
s1 type is: <type 'str'>
'10' < '9'
'10' != '9'
'10' is not '9'
#  can also compare numbers 
s1 type is: <type 'int'>
9 < 10
9 != 10
9 is not 10

#1.1. logic operator for "or"
d=-1; 
if [ $d -eq 0 ] || [ $d -lt 0 ]; then echo "$d<=0"; fi

#2.2. alternative expression
d=-1
if [[ $d -eq 0 || $d -lt 0 ]]; then echo "$d<=0"; fi
d=1
if (( $d ==  0 || $d < 0 )); then echo "$d<=0"; fi

-------output----------

#1.1. logic operator for or
-1<=0

#2.2. alternative expression
-1<=0

#1.1. logic operator for "or"
$d=-1;
#  similar to (()) in bash
if(($d==0)||($d<0)) {print "$d<=0"}

-------output----------

#1.1. logic operator for "or"
#  similar to (()) in bash
-1<=0

#1.1. logic operator for "or"
d=-1
if d==0 | d<0: print str(d)+"<=0"

#2.2. alternative expression
d=-1
if (d==0)|(d<0): print str(d)+"<=0"
if d==0 or d<0: print str(d)+"<=0"

-------output----------

#1.1. logic operator for "or" 
-1<=0

#2.2. alternative expression 
-1<=0
-1<=0