Update awk.html.markdown

1 files changed, 134 insertions, 110 deletions

diff --git a/awk.html.markdown b/awk.html.markdown
index de26c0a1..3d2c4ccb 100644
--- a/awk.html.markdown
+++ b/awk.html.markdown
@@ -6,14 +6,15 @@ contributors:
 
 ---
 
-AWK is a standard tool on every POSIX-compliant UNIX system. It's like a
-stripped-down Perl, perfect for text-processing tasks and other scripting
-needs. It has a C-like syntax, but without semicolons, manual memory
-management, or static typing. It excels at text processing. You can call to it
-from a shell script, or you can use it as a stand-alone scripting language.
-
-Why use AWK instead of Perl? Mostly because AWK is part of UNIX. You can always
-count on it, whereas Perl's future is in question. AWK is also easier to read
+AWK is a standard tool on every POSIX-compliant UNIX system. It's like
+flex/lex, from the command-line, perfect for text-processing tasks and
+other scripting needs. It has a C-like syntax, but without mandatory
+semicolons (although, you should use them anyway, because they are required
+when you're writing one-liners, something AWK excells at), manual memory
+management, or static typing. It excels at text processing. You can call to
+it from a shell script, or you can use it as a stand-alone scripting language.
+
+Why use AWK instead of Perl? Readability. AWK is easier to read
 than Perl. For simple text-processing scripts, particularly ones that read
 files line by line and split on delimiters, AWK is probably the right tool for
 the job.
@@ -23,8 +24,23 @@ the job.
 
 # Comments are like this
 
-# AWK programs consist of a collection of patterns and actions. The most
-# important pattern is called BEGIN. Actions go into brace blocks.
+
+# AWK programs consist of a collection of patterns and actions.
+pattern1 { action; } # just like lex
+pattern2 { action; }
+
+# There is an implied loop and AWK automatically reads and parses each
+# record of each file supplied. Each record is split by the FS delimiter,
+# which defaults to white-space (multiple spaces,tabs count as one)
+# You cann assign FS either on the command line (-F C) or in your BEGIN
+# pattern
+
+# One of the special patterns is BEGIN. The BEGIN pattern is true
+# BEFORE any of the files are read. The END pattern is true after
+# an End-of-file from the last file (or standard-in if no files specified)
+# There is also an output field separator (OFS) that you can assign, which
+# defaults to a single space
+
 BEGIN {
 
     # BEGIN will run at the beginning of the program. It's where you put all
@@ -32,114 +48,116 @@ BEGIN {
     # have no text files, then think of BEGIN as the main entry point.
 
     # Variables are global. Just set them or use them, no need to declare..
-    count = 0
+    count = 0;
 
     # Operators just like in C and friends
-    a = count + 1
-    b = count - 1
-    c = count * 1
-    d = count / 1 # integer division
-    e = count % 1 # modulus
-    f = count ^ 1 # exponentiation
-
-    a += 1
-    b -= 1
-    c *= 1
-    d /= 1
-    e %= 1
-    f ^= 1
+    a = count + 1;
+    b = count - 1;
+    c = count * 1;
+    d = count / 1; # integer division
+    e = count % 1; # modulus
+    f = count ^ 1; # exponentiation
+
+    a += 1;
+    b -= 1;
+    c *= 1;
+    d /= 1;
+    e %= 1;
+    f ^= 1;
 
     # Incrementing and decrementing by one
-    a++
-    b--
+    a++;
+    b--;
 
     # As a prefix operator, it returns the incremented value
-    ++a
-    --b
+    ++a;
+    --b;
 
     # Notice, also, no punctuation such as semicolons to terminate statements
 
     # Control statements
     if (count == 0)
-        print "Starting with count of 0"
+        print "Starting with count of 0";
     else
-        print "Huh?"
+        print "Huh?";
 
     # Or you could use the ternary operator
-    print (count == 0) ? "Starting with count of 0" : "Huh?"
+    print (count == 0) ? "Starting with count of 0" : "Huh?";
 
     # Blocks consisting of multiple lines use braces
     while (a < 10) {
         print "String concatenation is done" " with a series" " of"
-            " space-separated strings"
-        print a
+            " space-separated strings";
+        print a;
 
-        a++
+        a++;
     }
 
     for (i = 0; i < 10; i++)
-        print "Good ol' for loop"
+        print "Good ol' for loop";
 
     # As for comparisons, they're the standards:
-    a < b   # Less than
-    a <= b  # Less than or equal
-    a != b  # Not equal
-    a == b  # Equal
-    a > b   # Greater than
-    a >= b  # Greater than or equal
+    # a < b   # Less than
+    # a <= b  # Less than or equal
+    # a != b  # Not equal
+    # a == b  # Equal
+    # a > b   # Greater than
+    # a >= b  # Greater than or equal
 
     # Logical operators as well
-    a && b  # AND
-    a || b  # OR
+    # a && b  # AND
+    # a || b  # OR
 
     # In addition, there's the super useful regular expression match
     if ("foo" ~ "^fo+$")
-        print "Fooey!"
+        print "Fooey!";
     if ("boo" !~ "^fo+$")
-        print "Boo!"
+        print "Boo!";
 
     # Arrays
-    arr[0] = "foo"
-    arr[1] = "bar"
-    # Unfortunately, there is no other way to initialize an array. Ya just
-    # gotta chug through every value line by line like that.
-
-    # You also have associative arrays
-    assoc["foo"] = "bar"
-    assoc["bar"] = "baz"
+    arr[0] = "foo";
+    arr[1] = "bar";
+    
+    # You can also initialize an array with the built-in function split()
+    
+    n = split("foo:bar:baz", arr, ":");
+   
+    # You also have associative arrays (actually, they're all associative arrays)
+    assoc["foo"] = "bar";
+    assoc["bar"] = "baz";
 
     # And multi-dimensional arrays, with some limitations I won't mention here
-    multidim[0,0] = "foo"
-    multidim[0,1] = "bar"
-    multidim[1,0] = "baz"
-    multidim[1,1] = "boo"
+    multidim[0,0] = "foo";
+    multidim[0,1] = "bar";
+    multidim[1,0] = "baz";
+    multidim[1,1] = "boo";
 
     # You can test for array membership
     if ("foo" in assoc)
-        print "Fooey!"
+        print "Fooey!";
 
     # You can also use the 'in' operator to traverse the keys of an array
     for (key in assoc)
-        print assoc[key]
+        print assoc[key];
 
     # The command line is in a special array called ARGV
     for (argnum in ARGV)
-        print ARGV[argnum]
+        print ARGV[argnum];
 
     # You can remove elements of an array
     # This is particularly useful to prevent AWK from assuming the arguments
     # are files for it to process
-    delete ARGV[1]
+    delete ARGV[1];
 
     # The number of command line arguments is in a variable called ARGC
-    print ARGC
+    print ARGC;
 
     # AWK has several built-in functions. They fall into three categories. I'll
     # demonstrate each of them in their own functions, defined later.
 
-    return_value = arithmetic_functions(a, b, c)
-    string_functions()
-    io_functions()
+    return_value = arithmetic_functions(a, b, c);
+    string_functions();
+    io_functions();
 }
 
 # Here's how you define a function
@@ -159,26 +177,26 @@ function arithmetic_functions(a, b, c,     d) {
     # Now, to demonstrate the arithmetic functions
 
     # Most AWK implementations have some standard trig functions
-    localvar = sin(a)
-    localvar = cos(a)
-    localvar = atan2(b, a) # arc tangent of b / a
+    localvar = sin(a);
+    localvar = cos(a);
+    localvar = atan2(b, a); # arc tangent of b / a
 
     # And logarithmic stuff
-    localvar = exp(a)
-    localvar = log(a)
+    localvar = exp(a);
+    localvar = log(a);
 
     # Square root
-    localvar = sqrt(a)
+    localvar = sqrt(a);
 
     # Truncate floating point to integer
-    localvar = int(5.34) # localvar => 5
+    localvar = int(5.34); # localvar => 5
 
     # Random numbers
-    srand() # Supply a seed as an argument. By default, it uses the time of day
-    localvar = rand() # Random number between 0 and 1.
+    srand(); # Supply a seed as an argument. By default, it uses the time of day
+    localvar = rand(); # Random number between 0 and 1.
 
     # Here's how to return a value
-    return localvar
+    return localvar;
 }
 
 function string_functions(    localvar, arr) {
@@ -188,61 +206,66 @@ function string_functions(    localvar, arr) {
 
     # Search and replace, first instance (sub) or all instances (gsub)
     # Both return number of matches replaced
-    localvar = "fooooobar"
-    sub("fo+", "Meet me at the ", localvar) # localvar => "Meet me at the bar"
-    gsub("e+", ".", localvar) # localvar => "m..t m. at th. bar"
+    localvar = "fooooobar";
+    sub("fo+", "Meet me at the ", localvar); # localvar => "Meet me at the bar"
+    gsub("e+", ".", localvar); # localvar => "m..t m. at th. bar"
 
     # Search for a string that matches a regular expression
     # index() does the same thing, but doesn't allow a regular expression
-    match(localvar, "t") # => 4, since the 't' is the fourth character
+    match(localvar, "t"); # => 4, since the 't' is the fourth character
 
     # Split on a delimiter
-    split("foo-bar-baz", arr, "-") # a => ["foo", "bar", "baz"]
+    n = split("foo-bar-baz", arr, "-"); # a[1] = "foo"; a[2] = "bar"; a[3] = "baz"; n = 3
 
     # Other useful stuff
-    sprintf("%s %d %d %d", "Testing", 1, 2, 3) # => "Testing 1 2 3"
-    substr("foobar", 2, 3) # => "oob"
-    substr("foobar", 4) # => "bar"
-    length("foo") # => 3
-    tolower("FOO") # => "foo"
-    toupper("foo") # => "FOO"
+    sprintf("%s %d %d %d", "Testing", 1, 2, 3); # => "Testing 1 2 3"
+    substr("foobar", 2, 3); # => "oob"
+    substr("foobar", 4); # => "bar"
+    length("foo"); # => 3
+    tolower("FOO"); # => "foo"
+    toupper("foo"); # => "FOO"
 }
 
 function io_functions(    localvar) {
 
     # You've already seen print
-    print "Hello world"
+    print "Hello world";
 
     # There's also printf
-    printf("%s %d %d %d\n", "Testing", 1, 2, 3)
+    printf("%s %d %d %d\n", "Testing", 1, 2, 3);
 
     # AWK doesn't have file handles, per se. It will automatically open a file
     # handle for you when you use something that needs one. The string you used
     # for this can be treated as a file handle, for purposes of I/O. This makes
-    # it feel sort of like shell scripting:
+    # it feel sort of like shell scripting, but to get the same output, the string
+    # must match exactly, so use a vaiable:
+    
+    outfile = "/tmp/foobar.txt";
 
-    print "foobar" >"/tmp/foobar.txt"
+    print "foobar" > outfile;
 
-    # Now the string "/tmp/foobar.txt" is a file handle. You can close it:
-    close("/tmp/foobar.txt")
+    # Now the string outfile is a file handle. You can close it:
+    close(outfile);
 
     # Here's how you run something in the shell
-    system("echo foobar") # => prints foobar
+    system("echo foobar"); # => prints foobar
 
     # Reads a line from standard input and stores in localvar
-    getline localvar
+    getline localvar;
 
-    # Reads a line from a pipe
-    "echo foobar" | getline localvar # localvar => "foobar"
-    close("echo foobar")
+    # Reads a line from a pipe (again, use a string so you close it properly)
+    cmd = "echo foobar";
+    cmd | getline localvar; # localvar => "foobar"
+    close(cmd);
 
     # Reads a line from a file and stores in localvar
-    getline localvar <"/tmp/foobar.txt"
-    close("/tmp/foobar.txt")
+    infile = "/tmp/foobar.txt";
+    getline localvar < infile; 
+    close(infile);
 }
 
 # As I said at the beginning, AWK programs consist of a collection of patterns
-# and actions. You've already seen the all-important BEGIN pattern. Other
+# and actions. You've already seen the BEGIN pattern. Other
 # patterns are used only if you're processing lines from files or standard
 # input.
 #
@@ -257,7 +280,7 @@ function io_functions(    localvar) {
     # expression, /^fo+bar$/, and will be skipped for any line that fails to
     # match it. Let's just print the line:
 
-    print
+    print;
 
     # Whoa, no argument! That's because print has a default argument: $0.
     # $0 is the name of the current line being processed. It is created
@@ -268,16 +291,16 @@ function io_functions(    localvar) {
     # does. And, like the shell, each field can be access with a dollar sign
 
     # This will print the second and fourth fields in the line
-    print $2, $4
+    print $2, $4;
 
     # AWK automatically defines many other variables to help you inspect and
     # process each line. The most important one is NF
 
     # Prints the number of fields on this line
-    print NF
+    print NF;
 
     # Print the last field on this line
-    print $NF
+    print $NF;
 }
 
 # Every pattern is actually a true/false test. The regular expression in the
@@ -286,7 +309,7 @@ function io_functions(    localvar) {
 # currently processing. Thus, the complete version of it is this:
 
 $0 ~ /^fo+bar$/ {
-    print "Equivalent to the last pattern"
+    print "Equivalent to the last pattern";
 }
 
 a > 0 {
@@ -315,10 +338,10 @@ a > 0 {
 BEGIN {
 
     # First, ask the user for the name
-    print "What name would you like the average age for?"
+    print "What name would you like the average age for?";
 
     # Get a line from standard input, not from files on the command line
-    getline name <"/dev/stdin"
+    getline name < "/dev/stdin";
 }
 
 # Now, match every line whose first field is the given name
@@ -335,8 +358,8 @@ $1 == name {
     # ...etc. There are plenty more, documented in the man page.
 
     # Keep track of a running total and how many lines matched
-    sum += $3
-    nlines++
+    sum += $3;
+    nlines++;
 }
 
 # Another special pattern is called END. It will run after processing all the
@@ -348,7 +371,7 @@ $1 == name {
 
 END {
     if (nlines)
-        print "The average age for " name " is " sum / nlines
+        print "The average age for " name " is " sum / nlines;
 }
 
 ```
@@ -357,3 +380,4 @@ Further Reading:
 * [Awk tutorial](http://www.grymoire.com/Unix/Awk.html)
 * [Awk man page](https://linux.die.net/man/1/awk)
 * [The GNU Awk User's Guide](https://www.gnu.org/software/gawk/manual/gawk.html) GNU Awk is found on most Linux systems.
+* [AWK one-liner collection](http://tuxgraphics.org/~guido/scripts/awk-one-liner.html)