pallet

Library for Cross-Platform Development

Provides support for expressive idioms typical of scripting languages, for writing portable code that runs everywhere.

• Supported Scala Versions

  • scala 3.x

• Tested Target environments

  • Linux
  • Darwin/OSX
  • Windows
    • Cygwin64
    • Msys64
    • Mingw64
    • Git-bash
    • WSL Linux

Usage

To use pallet in an SBT project, add this dependency to build.sbt

  "org.vastblue" % "pallet_3" % "0.10.8"

For scala or scala-cli scripts, see examples below.

TL;DR

Simplicity and Universal Portability:

• Use scala instead of bash or python for portable general purpose scripting
• Publish universal scala scripts, rather than multiple OS-customized versions
• Script as though you're running in Linux, even on Windows or Mac.
• Convenient runtime branching based on runtime environment:

#!/usr/bin/env -S scala-cli shebang

//> using lib "org.vastblue::pallet::0.10.8"
import vastblue.pallet.*

  printf("uname / osType / osName:\n%s\n", s"platform info: ${unameLong} / ${osType} / ${osName}")
  if (isLinux) {
    // uname is "Linux"
    printf("hello Linux\n")
  } else if (isDarwin) {
    // uname is "Darwin*"
    printf("hello Mac\n")
  } else if (isWinshell) {
    // isWinshell: Boolean = isMsys | isCygwin | isMingw | isGitSdk | isGitbash
    printf("hello %s\n", unameShort)
  } else if (envOrEmpty("MSYSTEM").nonEmpty) {
    printf("hello %s\n", envOrEmpty("MSYSTEM"))
  } else {
    assert(isWindows, s"unknown environment: ${unameLong} / ${osType} / ${osName}")
    printf("hello Windows\n")
  }

• extends the range of scala scripting: Example: read process command lines from /proc/$PID/cmdline files

#!/usr/bin/env -S scala -deprecation -cp target/scala-3.3.3/classes

import vastblue.pallet.*
import vastblue.file.ProcfsPaths.cmdlines

var verbose = false
def main(args: Array[String]): Unit = {
  for (arg <- args) {
    arg match {
    case "-v" =>
      verbose = true
    }
  }
  if (isLinux || isWinshell) {
    printf("script name: %s\n\n", scriptName)
    // find /proc/[0-9]+/cmdline files
    for ((procfile, cmdline) <- cmdlines) {
      if (verbose || cmdline.contains(scriptName)) {
        printf("%s\n", procfile)
        printf("%s\n\n", cmdline)
      }
    }
  } else {
    printf("procfs filesystem not supported in os [%s]\n", osType)
  }
}

$ jsrc/procCmdline.sc

output when run from a Windows Msys64 bash session:

script name: jsrc/procCmdline.sc

/proc/32314/cmdline
'C:\opt\jdk\bin\java.exe' '-Dscala.home=C:/opt/scala' '-classpath' 'C:/opt/scala/lib/scala-library-2.13.10.jar;C:/opt/scala/lib/scala3-library_3-3.3.3.jar;C:/opt/scala/lib/scala-asm-9.5.0-scala-1.jar;C:/opt/scala/lib/compiler-interface-1.3.5.jar;C:/opt/scala/lib/scala3-interfaces-3.3.3.jar;C:/opt/scala/lib/scala3-compiler_3-3.3.3.jar;C:/opt/scala/lib/tasty-core_3-3.3.3.jar;C:/opt/scala/lib/scala3-staging_3-3.3.3.jar;C:/opt/scala/lib/scala3-tasty-inspector_3-3.3.3.jar;C:/opt/scala/lib/jline-reader-3.19.0.jar;C:/opt/scala/lib/jline-terminal-3.19.0.jar;C:/opt/scala/lib/jline-terminal-jna-3.19.0.jar;C:/opt/scala/lib/jna-5.3.1.jar;;' 'dotty.tools.MainGenericRunner' '-classpath' 'C:/opt/scala/lib/scala-library-2.13.10.jar;C:/opt/scala/lib/scala3-library_3-3.3.3.jar;C:/opt/scala/lib/scala-asm-9.5.0-scala-1.jar;C:/opt/scala/lib/compiler-interface-1.3.5.jar;C:/opt/scala/lib/scala3-interfaces-3.3.3.jar;C:/opt/scala/lib/scala3-compiler_3-3.3.3.jar;C:/opt/scala/lib/tasty-core_3-3.3.3.jar;C:/opt/scala/lib/scala3-staging_3-3.3.3.jar;C:/opt/scala/lib/scala3-tasty-inspector_3-3.3.3.jar;C:/opt/scala/lib/jline-reader-3.19.0.jar;C:/opt/scala/lib/jline-terminal-3.19.0.jar;C:/opt/scala/lib/jline-terminal-jna-3.19.0.jar;C:/opt/scala/lib/jna-5.3.1.jar;;' '-deprecation' '-cp' 'target/scala-3.3.3/classes' './procCmdline.sc'

/proc/32274/cmdline
'bash' '/c/opt/scala/bin/scala' '-deprecation' '-cp' 'target/scala-3.3.3/classes' './procCmdline.sc'

Example #2: write and read .csv files:

#!/usr/bin/env -S scala -cp target/scala-3.3.3/classes
//package vastblue

import vastblue.pallet.*

object CsvWriteRead {
  def main(args: Array[String]): Unit = {
    val testFiles = Seq("tabTest.csv", "commaTest.csv")
    for (filename <- testFiles){
      val testFile: Path = filename.toPath

      if (!testFile.exists) {
        // create tab-delimited and comma-delimited test files
        val delim: String = if filename.startsWith("tab") then "\t" else ","
        testFile.withWriter() { w =>
          w.printf(s"1st${delim}2nd${delim}3rd\n")
          w.printf(s"A${delim}B${delim}C\n")
        }
      }

      assert(testFile.isFile)
      printf("\n# filename: %s\n", testFile.norm)
      // display file text lines
      for ((line: String, i: Int) <- testFile.lines.zipWithIndex){
        printf("%d: %s\n", i, line)
      }
      // display file csv rows
      for (row: Seq[String] <- testFile.csvRows){
        printf("%s\n", row.mkString("|"))
      }
    }
  }
}

$ time jsrc/csvWriteRead.sc

Output:

# filename: C:/Users/philwalk/workspace/pallet/tabTest.csv
0: 1st  2nd     3rd
1: A    B       C
1st|2nd|3rd
A|B|C

# filename: C:/Users/philwalk/workspace/pallet/commaTest.csv
0: 1st,2nd,3rd
1: A,B,C
1st|2nd|3rd
A|B|C

real    0m4.269s
user    0m0.135s
sys     0m0.411s

Requirements

In Windows, requires a posix shell: (MSYS64, CYGWIN64, or WSL)

In Darwin/OSX, requires homebrew or similar.

Best with a recent version of coreutils: (e.g., ubuntu: 8.32-4.1ubuntu1, osx: stable 9.4)

Concept

• Concise, expressive and readable scripting idioms
• correct portable handling of command line args
• vastblue.file.Paths is a java.nio.file.Paths drop-in replacement that:
  • correctly handles mounted posix paths
  • returns ordinary java.nio.file.Path objects

Examples below illustrate some of the capabilities.

Background

If you work in diverse environments, you generally must customize scripts for each environment:

• in Linux, Darwin/Osx, shell or python scripts
• in Windows, batch files, powershell scripts, or other Windows-specific tools

Hard to make scala scripts portable across Linux, Osx, Windows, because the jvm doesn't support filesystem abstractions of cygwin64, msys64, etc.

Most platforms other than Windows are unix-like, but:

• differing conventions and incompatibilities:
  • Linux / OSX symantics of /usr/bin/env, etc.

This library provides the missing piece.

Choices to be made when using scala as a general purpose scripting language include:

• how to manage the classpath
• learning cross-platform coding techniques

The Classpath

The various approaches to managing classpaths fall into two categories. In addition to installing scripts, client systems must either:

• install scala-cli
• install required jars plus an associated @atFile

If scala-cli is installed, the classpath is fully managed for you. If required jars plus associated @atFile are installed, your scripts must either:

• reference @<path-to-atFile> in the shebang line
• set environment variable SCALA_OPTS=@<path-to-atFile>

To support Darwin/Osx, an absolute path to an @atFile is required in the shebang line. Example portable shebang line: #!/usr/bin/env -S scala @/opt/atFiles/.scala3cp

Alternatively, if SCALA_OPTS is defined: #!/usr/bin/env -S scala

Setup for running the example scripts:

A good option for writing scala scripts is scala-cli, and some example scripts are written for it. Each scala-cli script specifies required dependency internally, and the classpath is managed for you.

A scala-cli alternative is to create an @atFile containing the -classpath definition.

Some differences to be aware of between scala-cli scripts and conventional scala scripts:

• a scala-cli script declares dependencies within the script via special comments
• if main() is defined, it must be explicitly called within a scala-cli script
• startup times the two script types differ, even after the initial compile invocation. On my Windows box:
  • 4 seconds for scala-cli before printing hello world
  • 2 seconds for scala scripts (SCALA_CLI=-save @/Users/username/scala3cp)

Defining the classpath

For a per-user classpath atFile, define your classpath in a file named, e.g., /Users/username/.scala3cp. To include the scala3 version of this library, for example, the @file might contain:

-classpath /Users/username/.ivy2/local/org.vastblue/pallet_3/0.10.8/jars/pallet_3.jar

With this configuration, your scala 3 shebang line will look like this:

#!/usr/bin/env -S scala @${HOME}/scala3cp

In Darwin/Osx the ${HOME} path must be explicit, due to /usr/bin/env semantics. The alternative is to reference the @atFile via SCALA_OPTS=@/Users/username/scala3cp rather than in the shebang line.

Examples below assume classpath and other options are defined by the SCALA_CLI variable.

Note that if classpath is also defined in the shebang line, it will append to the classpath defined in SCALA_CLI.

Example script: display the native path and the number of lines in /etc/fstab

This example might surprise developers working in a Windows posix shell, since jvm languages normally cannot see posix file paths that aren't also legal Windows paths.

#!/ usr / bin / env -S scala

import vastblue.pallet.*
import vastblue.Platform.*

object Fstab {
  def main(args: Array[String]): Unit = {
    // `posixroot` is the native path corresponding to "/"
    // display the native path and lines.size of /etc/fstab
    val p = Paths.get("/etc/fstab")
    printf("env: %-10s| posixroot: %-12s| %-22s| %d lines\n",
      _uname("-o"), posixroot, p.norm, p.lines.size)
  }
}

Equivalent Scala-cli version of the same script:

#!/ usr / bin / env -S scala -cli shebang

//> using scala "3.3.3"
//> using lib "org.vastblue::pallet::0.10.8"

import vastblue.pallet.*
import vastblue.Platform.*

object FstabCli {
  def main(args: Array[String]): Unit = {
    // `posixroot` is the native path corresponding to "/"
    // display the native path and lines.size of /etc/fstab
    val p = Paths.get("/etc/fstab")
    printf("env: %-10s| posixroot: %-12s| %-22s| %d lines\n",
      _uname("-o"), posixroot, p.norm, p.lines.size)
  }
}

FstabCli.main(args)

Output of the previous example scripts on various platforms:

Linux Mint # env: GNU/Linux | posixroot: /           | /etc/fstab            | 21 lines
Darwin     # env: Darwin    | posixroot: /           | /etc/fstab            | 0 lines
WSL Ubuntu # env: GNU/Linux | posixroot: /           | /etc/fstab            | 6 lines
Cygwin64   # env: Cygwin    | posixroot: C:/cygwin64 | C:/cygwin64/etc/fstab | 24 lines
Msys64     # env: Msys      | posixroot: C:/msys64/  | C:/msys64/etc/fstab   | 22 lines

Note that on Darwin, there is no /etc/fstab file, so the Path#lines extension returns Nil.

Example scala-cli script:

#!/usr/bin/env -S scala-cli shebang

//> using scala "3.3.3"
//> using lib "org.vastblue::pallet::0.10.8"

import vastblue.pallet.*

def main(args: Array[String]): Unit = {
  // list child directories of "."
  val cwd: Path = Paths.get(".")
  for ( p: Path <- cwd.paths.filter { _.isDirectory }) {
    printf("%s\n", p.norm)
  }
}
main(args)

Example scala3 script

#!/usr/bin/env -S scala -cp @./atFile

import vastblue.pallet.*

def main(args: Array[String]): Unit =
  // display native path of command-line provided filenames
  val dirs = for
    fname <- args
    p = Paths.get(fname)
    if p.isFile
  yield p.norm

  printf("%s\n", dirs.toList.mkString("\n"))

How to consistently access comand line arguments

The Windows jvm will sometimes expand glob arguments, even if double-quoted.

• https://stackoverflow.com/questions/37037375/trailing-asterisks-on-windows-jvm-command-line-args-are-globbed-in-cygwin-bash-s/37081167#37081167:~:text=This%20problem%20is%20caused,net/browse/JDK%2D8131329 This script demonstrates a consistent, portable way to get command line arguments.

#!/usr/bin/env -S scala
package vastblue

import vastblue.pallet.*

def main(args: Array[String]): Unit = {
  // display default args
  for (arg <- args) {
    printf("arg [%s]\n", arg)
  }
  // display extended and repaired args
  val argv = prepArgs(args.toSeq)
  for ((arg, i) <- argv.zipWithIndex) {
    printf(" %2d: [%s]\n", i, arg)
  }
}

Pass arguments with embedded spaces and glob expressions to see the difference between args and argv. Notice that argv has the script path in argv(0), similar to the standard in C

Using SCALA_OPTS environment variable

With scala 3, you can specify the classpath via an environment variable, permitting the use of a universal shebang line (a portability requirement).

• Create a classpath atFile named ${HOME}/scala3cp:
• define SCALA_OPTS (e.g., in ~/.bashrc):
  • export SCALA_OPTS="@${HOME}/scala3cp"

If you want to speed up subsequent calls to your scripts (after the initial compile-and-run invocation), you can add the -save option to your SCALA_OPTS variable:

• export SCALA_OPTS="@/${HOME}/scala3cp -save"

The -save option saves the compiled script to a jar file in the script parent directory, speeding up subsequent calls, which are equivalent to java -jar <jarfile>. The jar is self-contained, as it defines main class, classpath, etc. via the jar manifest.mf file.

Setup

• Windows: install one of the following:
  • MSYS64
  • CYGWIN64
  • WSL
• Linux: required packages:
  • sudo apt install coreutils
• Darwin/OSX:
  • brew install coreutils

How to Write Portable Scala Scripts

Things that maximize the odds of your script running on another system:

• use scala 3
• use posix file paths by default
• in Windows
  • represent paths internally with forward slashes and avoid drive letters
  • drive letter not needed for paths on the current working drive (often C:)
  • to access disks other than the working drive, mount them via /etc/fstab
  • vastblue.Paths.get() is can parse both posix and Windows filesystem paths
• don't assume path strings use java.nio.File.separator or sys.props("line.separator")
• use them to format output, as appropriate, never to parse path strings
• split strings with "(\r)?\n" rather than line.separator
  • split("\n") can leave carriage-return debris lines ends
• create java.nio.file.Path objects in either of two ways:
  • `vastblue.file.Paths.get("/etc/fstab")
  • "/etc/fstab".path // guaranteed to use vastblue.file.Paths.get()`
• if client needs glob expression command line arguments, val argv = prepArgs(args.toSeq)
  • this avoids exposure to the Windows jvm glob expansion bug, and
  • inserts script path or main method class as argv(0) (as in C/C++)
  • argv(0) script name available as input parameter affecting script behaviour