[bash/en] Provide example outputs for #549

bash.html.markdown

@@ -30,59 +30,62 @@ Nearly all examples below can be a part of a shell script or executed directly i
 # As you already figured, comments start with #. Shebang is also a comment.
 
 # Simple hello world example:
-echo Hello world!
+echo Hello world! # => Hello world!
 
 # Each command starts on a new line, or after semicolon:
 echo 'This is the first line'; echo 'This is the second line'
+# => This is the first line
+# => This is the second line
 
 # Declaring a variable looks like this:
 Variable="Some string"
 
 # But not like this:
-Variable = "Some string"
+Variable = "Some string" # => returns error "Variable: command not found"
 # Bash will decide that Variable is a command it must execute and give an error
 # because it can't be found.
 
 # Or like this:
-Variable= 'Some string'
+Variable= 'Some string' # => returns error: "Some string: command not found"
 # Bash will decide that 'Some string' is a command it must execute and give an
 # error because it can't be found. (In this case the 'Variable=' part is seen
 # as a variable assignment valid only for the scope of the 'Some string'
 # command.)
 
 # Using the variable:
-echo $Variable
+echo $Variable # => Some string
-echo "$Variable"
+echo "$Variable" # => Some string
-echo '$Variable'
+echo '$Variable' # => Some string
 # When you use the variable itself — assign it, export it, or else — you write
 # its name without $. If you want to use the variable's value, you should use $.
 # Note that ' (single quote) won't expand the variables!
 
 # Parameter expansion ${ }:
-echo ${Variable}
+echo ${Variable} # => Some string
 # This is a simple usage of parameter expansion
 # Parameter Expansion gets a value from a variable.  It "expands" or prints the value
 # During the expansion time the value or parameter are able to be modified
 # Below are other modifications that add onto this expansion
 
 # String substitution in variables
-echo ${Variable/Some/A}
+echo ${Variable/Some/A} # => A string
 # This will substitute the first occurrence of "Some" with "A"
 
 # Substring from a variable
 Length=7
-echo ${Variable:0:Length}
+echo ${Variable:0:Length} # => Some st
 # This will return only the first 7 characters of the value
 
 # Default value for variable
 echo ${Foo:-"DefaultValueIfFooIsMissingOrEmpty"} 
+# => DefaultValueIfFooIsMissingOrEmpty
 # This works for null (Foo=) and empty string (Foo=""); zero (Foo=0) returns 0.
 # Note that it only returns default value and doesn't change variable value.
 
 # Brace Expansion { }
 # Used to generate arbitrary strings
-echo {1..10}
+echo {1..10} # => 1 2 3 4 5 6 7 8 9 10
-echo {a..z}
+echo {a..z} # => a b c d e f g h i j k l m n o p q r s t u v w x y z
 # This will output the range from the start value to the end value
 
 # Builtin variables:
@@ -121,6 +124,7 @@ then
 else
     echo "Your name is your username"
 fi
+# True if the value of $Name is not equal to the current user's login username
 
 # NOTE: if $Name is empty, bash sees the above condition as:
 if [ != $USER ]
@@ -133,7 +137,11 @@ if [ "" != $USER ] ...
 
 # There is also conditional execution
 echo "Always executed" || echo "Only executed if first command fails"
+# => Always executed
 echo "Always executed" && echo "Only executed if first command does NOT fail"
+# => Always executed
+# => Only executed if first command does NOT fail
+
 
 # To use && and || with if statements, you need multiple pairs of square brackets:
 if [ "$Name" == "Steve" ] && [ "$Age" -eq 15 ]
@@ -147,12 +155,12 @@ then
 fi
 
 # Expressions are denoted with the following format:
-echo $(( 10 + 5 ))
+echo $(( 10 + 5 )) # => 15
 
 # Unlike other programming languages, bash is a shell so it works in the context
 # of a current directory. You can list files and directories in the current
 # directory with the ls command:
-ls
+ls # Lists the files and subdirectories contained in the current directory
 
 # These commands have options that control their execution:
 ls -l # Lists every file and directory on a separate line
@@ -169,7 +177,10 @@ cat file.txt
 
 # We can also read the file using `cat`:
 Contents=$(cat file.txt)
-echo "START OF FILE\n$Contents\nEND OF FILE"
+echo "START OF FILE\n$Contents\nEND OF FILE" # "\n" prints a new line character
+# => START OF FILE
+# => [contents of file.txt]
+# => END OF FILE
 
 # Use `cp` to copy files or directories from one place to another.
 # `cp` creates NEW versions of the sources,
@@ -203,6 +214,8 @@ pwd # still in first directory
 mkdir myNewDir
 # The `-p` flag causes new intermediate directories to be created as necessary.
 mkdir -p myNewDir/with/intermediate/directories
+# if the intermediate directories didn't already exist, running the above
+# command without the `-p` flag would return an error
 
 # You can redirect command input and output (stdin, stdout, and stderr).
 # Read from stdin until ^EOF$ and overwrite hello.py with the lines
@@ -217,12 +230,15 @@ for line in sys.stdin:
     print(line, file=sys.stdout)
 EOF
 
-# Run hello.py with various stdin, stdout, and stderr redirections:
+# Run the hello.py Python script with various stdin, stdout, and 
-python hello.py < "input.in"
+# stderr redirections:
-python hello.py > "output.out"
+python hello.py < "input.in" # pass input.in as input to the script
-python hello.py 2> "error.err"
+python hello.py > "output.out" # redirect output from the script to output.out
-python hello.py > "output-and-error.log" 2>&1
+python hello.py 2> "error.err" # redirect error output to error.err
-python hello.py > /dev/null 2>&1
+python hello.py > "output-and-error.log" 2>&1 # redirect both output and
+																						  # errors to output-and-error.log
+python hello.py > /dev/null 2>&1 # redirect all output and errors to 
+																 # the black hole, /dev/null, i.e., no output
 # The output error will overwrite the file if it exists,
 # if you want to append instead, use ">>":
 python hello.py >> "output.out" 2>> "error.err"
@@ -269,12 +285,19 @@ for Variable in {1..3}
 do
     echo "$Variable"
 done
+# => 1
+# => 2
+# => 3
+
 
 # Or write it the "traditional for loop" way:
 for ((a=1; a <= 3; a++))
 do
     echo $a
 done
+# => 1
+# => 2
+# => 3
 
 # They can also be used to act on files..
 # This will run the command 'cat' on file1 and file2
@@ -296,6 +319,7 @@ do
     echo "loop body here..."
     break
 done
+# => loop body here...
 
 # You can also define functions
 # Definition:
@@ -306,6 +330,11 @@ function foo ()
     echo "This is a function"
     return 0
 }
+# Call the function `foo` with two arguments, arg1 and arg2:
+foo arg1 arg2
+# => Arguments work just like script arguments: arg1 arg2
+# => And: arg1 arg2...
+# => This is a function
 
 # or simply
 bar ()
@@ -313,6 +342,8 @@ bar ()
     echo "Another way to declare functions!"
     return 0
 }
+# Call the function `bar` with no arguments:
+bar # => Another way to declare functions!
 
 # Calling your function
 foo "My name is" $Name
@@ -320,25 +351,35 @@ foo "My name is" $Name
 # There are a lot of useful commands you should learn:
 # prints last 10 lines of file.txt
 tail -n 10 file.txt
+
 # prints first 10 lines of file.txt
 head -n 10 file.txt
+
 # sort file.txt's lines
 sort file.txt
+
 # report or omit repeated lines, with -d it reports them
 uniq -d file.txt
+
 # prints only the first column before the ',' character
 cut -d ',' -f 1 file.txt
-# replaces every occurrence of 'okay' with 'great' in file.txt, (regex compatible)
+
+# replaces every occurrence of 'okay' with 'great' in file.txt
+# (regex compatible)
 sed -i 's/okay/great/g' file.txt
+
 # print to stdout all lines of file.txt which match some regex
 # The example prints lines which begin with "foo" and end in "bar"
 grep "^foo.*bar$" file.txt
+
 # pass the option "-c" to instead print the number of lines matching the regex
 grep -c "^foo.*bar$" file.txt
+
 # Other useful options are:
 grep -r "^foo.*bar$" someDir/ # recursively `grep`
 grep -n "^foo.*bar$" file.txt # give line numbers
 grep -rI "^foo.*bar$" someDir/ # recursively `grep`, but ignore binary files
+
 # perform the same initial search, but filter out the lines containing "baz"
 grep "^foo.*bar$" file.txt | grep -v "baz"
 
@@ -346,8 +387,9 @@ grep "^foo.*bar$" file.txt | grep -v "baz"
 # and not the regex, use fgrep (or grep -F)
 fgrep "foobar" file.txt
 
-# trap command allows you to execute a command when a signal is received by your script.
+# The trap command allows you to execute a command whenever your script 
-# Here trap command will execute rm if any one of the three listed signals is received.
+# receives a signal. Here, trap will execute `rm` if it receives any of the 
+# three listed signals.
 trap "rm $TEMP_FILE; exit" SIGHUP SIGINT SIGTERM
 
 # `sudo` is used to perform commands as the superuser