Implement Shebang Parameter

This will enable utilizing the parallel application as an interpreter.

4 files changed, 67 insertions, 28 deletions

diff --git a/README.md b/README.md
index bd74c72..25041ef 100644
--- a/README.md
+++ b/README.md
@@ -15,6 +15,9 @@ See the [to-do list](https://github.com/mmstick/parallel/blob/master/TODO.md) fo
 ## Benchmark Comparison to GNU Parallel
 
 ### GNU Parallel
+
+#### Printing 1 to 10,000 in parallel
+
 ```
 ~/D/parallel (master) $ seq 1 10000 | time -v /usr/bin/parallel echo > /dev/null
     Command being timed: "/usr/bin/parallel echo"
@@ -42,6 +45,8 @@ See the [to-do list](https://github.com/mmstick/parallel/blob/master/TODO.md) fo
     Exit status: 0
 ```
 
+#### Cat the contents of every binary in /usr/bin
+
 ```
 ~/D/parallel (master) $ time -v /usr/bin/parallel cat ::: /usr/bin/* > /dev/null
     User time (seconds): 71.71
@@ -72,26 +77,28 @@ See the [to-do list](https://github.com/mmstick/parallel/blob/master/TODO.md) fo
 
 It's highly recommend to compile Parallel with MUSL instead of glibc, as this reduces memory consumption in half and doubles performance.
 
+#### Printing 1 to 10,000 in parallel
+
 ```
 ~/D/parallel (master) $ seq 1 10000 | time -v target/release/x86_64-unknown-linux-musl/parallel echo > /dev/null
-    Command being timed: "target/x86_64-unknown-linux-musl/release/parallel echo"
-    User time (seconds): 0.55
-    System time (seconds): 3.45
-    Percent of CPU this job got: 65%
-    Elapsed (wall clock) time (h:mm:ss or m:ss): 0:06.14
+Command being timed: "target/x86_64-unknown-linux-musl/release/parallel echo"
+    User time (seconds): 0.48
+    System time (seconds): 2.85
+    Percent of CPU this job got: 104%
+    Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.20
     Average shared text size (kbytes): 0
     Average unshared data size (kbytes): 0
     Average stack size (kbytes): 0
     Average total size (kbytes): 0
     Maximum resident set size (kbytes): 1768
     Average resident set size (kbytes): 0
-    Major (requiring I/O) page faults: 1
-    Minor (reclaiming a frame) page faults: 815825
-    Voluntary context switches: 72504
-    Involuntary context switches: 54392
+    Major (requiring I/O) page faults: 0
+    Minor (reclaiming a frame) page faults: 823754
+    Voluntary context switches: 82723
+    Involuntary context switches: 64834
     Swaps: 0
-    File system inputs: 8
-    File system outputs: 352
+    File system inputs: 0
+    File system outputs: 320
     Socket messages sent: 0
     Socket messages received: 0
     Signals delivered: 0
@@ -99,25 +106,27 @@ It's highly recommend to compile Parallel with MUSL instead of glibc, as this re
     Exit status: 0
 ```
 
+#### Cat the contents of every binary in /usr/bin
+
 ```
 ~/D/parallel (master) $ time -v target/release/x86_64-unknown-linux-musl/release/parallel cat ::: /usr/bin/* > /dev/null
-    User time (seconds): 1.27
-    System time (seconds): 5.07
-    Percent of CPU this job got: 138%
-    Elapsed (wall clock) time (h:mm:ss or m:ss): 0:04.58
+    User time (seconds): 0.96
+    System time (seconds): 4.61
+    Percent of CPU this job got: 192%
+    Elapsed (wall clock) time (h:mm:ss or m:ss): 0:02.89
     Average shared text size (kbytes): 0
     Average unshared data size (kbytes): 0
     Average stack size (kbytes): 0
     Average total size (kbytes): 0
-    Maximum resident set size (kbytes): 1844
+    Maximum resident set size (kbytes): 1868
     Average resident set size (kbytes): 0
     Major (requiring I/O) page faults: 0
-    Minor (reclaiming a frame) page faults: 350701
-    Voluntary context switches: 67739
-    Involuntary context switches: 44271
+    Minor (reclaiming a frame) page faults: 350216
+    Voluntary context switches: 68772
+    Involuntary context switches: 40085
     Swaps: 0
-    File system inputs: 0
-    File system outputs: 480
+    File system inputs: 368
+    File system outputs: 416
     Socket messages sent: 0
     Socket messages received: 0
     Signals delivered: 0
@@ -137,8 +146,9 @@ parallel echo ::: 1 2 3 ::: A B C ::: D E F       // Permutate the inputs.
 parallel echo {} {1} {2} {3.} ::: 1 2 file.mkv    // {N} tokens are replaced by the Nth input argument
 parallel ::: "echo 1" "echo 2" "echo 3"           // If no command is supplied, the input arguments become commands.
 parallel 'cd {}; echo Directory: {}; echo - {}'   // Commands may be chained in the platform\'s shell.
-seq 1 10 | parallel 'echo {}'                           // If no input arguments are supplied, stdin will be read.
-seq 1 10 | parallel --pipe cat                       // Piping arguments to the standard input of the given command.
+seq 1 10 | parallel 'echo {}'                     // If no input arguments are supplied, stdin will be read.
+seq 1 10 | parallel --pipe cat                    // Piping arguments to the standard input of the given command.
+#!/usr/bin/parallel --shebang echo            // Ability to use within a shebang line.
 ```
 
 ## Manual
@@ -227,6 +237,7 @@ operates:
         instead supply the arguments directly to the standard input of each child process.
 - **-q**, **--quote**: Retains backslashes that are supplied as the command input.
 - **-s**, **--silent**, **--quiet**: Disables printing the standard output of running processes.
+- **--shebang**: Grants ability to utilize the parallel command as an interpreter via calling it within a shebang line.
 - **--shellquote**: Expands upon quote mode by escaping a wide variety of special characters.
 - **--timeout**: If a command runs for longer than a specified number of seconds, it will be killed with a SIGKILL.
 - **-v**, **--verbose**: Prints information about running processes.
diff --git a/TODO.md b/TODO.md
index 4724dde..a90dd12 100644
--- a/TODO.md
+++ b/TODO.md
@@ -10,8 +10,6 @@ The list is actively updated with each successful pull request.
     - Compress the outputs of a file if the file exceeds a certain length
 - Implement `memfree`
     - Only execute a task if memory consumption is below a certain threshold.
-- Implement `skip-first-line` and `shebang`
-    - Basically, enale the ability to use parallel in a shebang line
 - Implement `workdir` and `tempdir`
     - Allow the ability to change the default location of the temp and work directories
 - Fix quoting issues
diff --git a/src/arguments/man.rs b/src/arguments/man.rs
index 936840d..930853b 100644
--- a/src/arguments/man.rs
+++ b/src/arguments/man.rs
@@ -113,6 +113,10 @@ OPTIONS
     -s, --silent, --quiet:
         Disables printing the standard output of running processes.
 
+    --shebang:
+        Grants ability to utilize the parallel command as an interpreter via
+        calling it within a shebang line.
+
     --timeout:
         If a command runs for longer than a specified number of seconds, it will be
         killed with a SIGKILL.
@@ -142,6 +146,11 @@ EXAMPLES
     # Reading inputs from files and command arguments
     parallel 'echo {}' :::: list1 list2 ::: $(seq 1 10) :::: list3 list4
 
+    # Within a file, with each successive newline being an input argument
+    #!/usr/bin/parallel --shebang echo
+    1
+    2
+
 HOW IT WORKS
     The Parallel command consists of three phases: parsing, threading, and execution.
 
diff --git a/src/arguments/mod.rs b/src/arguments/mod.rs
index 11b5b18..7971be7 100644
--- a/src/arguments/mod.rs
+++ b/src/arguments/mod.rs
@@ -82,6 +82,8 @@ impl<'a> Args<'a> {
                 _  => (Mode::Arguments, 1)
             };
 
+            let mut shebang = false;
+
             if let Mode::Arguments = mode {
                 while let Some(argument) = arguments.get(index) {
                     index += 1;
@@ -144,6 +146,7 @@ impl<'a> Args<'a> {
                                 "pipe" => self.flags |= PIPE_IS_ENABLED,
                                 "quiet" | "silent" => self.flags |= QUIET_MODE,
                                 "quote" => quote = Quoting::Basic,
+                                // "shebang" => shebang = true,
                                 "shellquote" => quote = Quoting::Shell,
                                 "timeout" => {
                                     let val = arguments.get(index).ok_or(ParseErr::DelayNoValue)?;
@@ -163,6 +166,11 @@ impl<'a> Args<'a> {
                                     exit(0);
                                 }
                                 _ => {
+                                    if &argument[2..9] == "shebang" {
+                                        shebang = true;
+                                        comm.push_str(&argument[10..]);
+                                        break
+                                    }
                                     return Err(ParseErr::InvalidArgument(index-1));
                                 }
                             }
@@ -207,7 +215,12 @@ impl<'a> Args<'a> {
                 }
             }
 
-            parse_inputs(arguments, index, &mut current_inputs, &mut lists, &mut mode)?;
+            if shebang {
+                file_parse(&mut current_inputs, &arguments.last().unwrap())?;
+            } else {
+                parse_inputs(arguments, index, &mut current_inputs, &mut lists, &mut mode)?;
+            }
+
             number_of_arguments = write_inputs_to_disk(lists, current_inputs, max_args, &mut disk_buffer)?;
         }
 
@@ -491,8 +504,16 @@ fn parse_jobs(argument: &str, next_argument: Option<&String>, index: &mut usize)
 fn file_parse<P: AsRef<Path>>(inputs: &mut Vec<String>, path: P) -> Result<(), ParseErr> {
     let path = path.as_ref();
     let file = fs::File::open(path).map_err(|err| ParseErr::File(FileErr::Open(path.to_owned(), err)))?;
-    for line in BufReader::new(file).lines() {
-        if let Ok(line) = line { inputs.push(line); }
+    let mut buffer = BufReader::new(file).lines();
+    if let Some(line) = buffer.next() {
+        if let Ok(line) = line {
+            if !line.is_empty() && !line.starts_with("#!") { inputs.push(line); }
+        }
+    }
+    for line in buffer {
+        if let Ok(line) = line {
+            if !line.is_empty() { inputs.push(line); }
+        }
     }
     Ok(())
 }