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# Chapter 9 File, I/O and system operations

- File names
- Path search
- File stats
- Globbing and file listings
- Filesystem operations
- vmount
- File predicates
- IO functions
- Printing functions
- Value printing functions
- Higher-level IO functions

## 9.1 File names

### 9.1.1 file, dir

       $(file sequence) : File Sequence
          sequence : Sequence
       $(dir sequence) : Dir Sequence
          sequence : Sequence

The `file` and `dir` functions define location-independent references to files and directories. In `omake`, the commands to build a target are executed in the target's directory. Since there may be many directories in an `omake` project, the build system provides a way to construct a reference to a file in one directory, and use it in another without explicitly modifying the file name. The functions have the following syntax, where the name should refer to a file or directory.

For example, we can construct a reference to a file `foo` in the current directory.

       FOO = $(file foo)
       .SUBDIRS: bar

If the `FOO` variable is expanded in the `bar` subdirectory, it will expand to `../foo`.

These commands are often used in the top-level OMakefile to provide location-independent references to top-level directories, so that build commands may refer to these directories as if they were absolute.

       ROOT = $(dir .)
       LIB  = $(dir lib)
       BIN  = $(dir bin)

Once these variables are defined, they can be used in build commands in subdirectories as follows, where `$(BIN)` will expand to the location of the `bin` directory relative to the command being executed.

       install: hello
     cp hello $(BIN)

### 9.1.2 tmpfile

        $(tmpfile prefix) : File
        $(tmpfile prefix, suffix) : File
            prefix : String
            suffix : String

The `tmpfile` function returns the name of a fresh temporary file in the temporary directory.

### 9.1.3 in

       $(in dir, exp) : String Array
          dir : Dir
          exp : expression

The `in` function is closely related to the `dir` and `file` functions. It takes a directory and an expression, and evaluates the expression in that effective directory. For example, one common way to install a file is to define a symbol link, where the value of the link is relative to the directory where the link is created.

The following commands create links in the `$(LIB)` directory.

        FOO = $(file foo)
        install:
           ln -s $(in $(LIB), $(FOO)) $(LIB)/foo

Note that the `in` function only affects the expansion of `Node` (`File` and `Dir`) values.

### 9.1.4 basename

       $(basename files) : String Sequence
          files : String Sequence

The `basename` function returns the base names for a list of files. The basename is the filename with any leading directory components removed.

For example, the expression `$(basename dir1/dir2/a.out /etc/modules.conf /foo.ml)` evaluates to `a.out modules.conf foo.ml`.

### 9.1.5 dirname

       $(dirname files) : String Sequence
          files : String Sequence

The `dirname` function returns the directory name for a list of files. The directory name is the filename with the basename removed. If a name does not have a directory part, the directory is “.”

For example, the expression `$(dirname dir1\dir2\a.out /etc/modules.conf /foo.ml bar.ml)` evaluates to `dir1/dir2 /etc / .`.

Note: this function is different from the `dirof` function. The function `dirname` is simple a function over strings, while `dirof` is a function on filenames.

### 9.1.6 rootname

       $(rootname files) : String Sequence
          files : String Sequence

The `rootname` function returns the root name for a list of files. The rootname is the filename with the final suffix removed.

For example, the expression `$(rootname dir1/dir2/a.out /etc/a.b.c /foo.ml)` evaluates to `dir1/dir2/a /etc/a.b /foo`.

### 9.1.7 dirof

       $(dirof files) : Dir Sequence
          files : File Sequence

The `dirof` function returns the directory for each of the listed files.

For example, the expression `$(dirof dir/dir2/a.out /etc/modules.conf /foo.ml)` evaluates to the directories `dir1/dir2 /etc /`.

### 9.1.8 fullname

       $(fullname files) : String Sequence
          files : File Sequence

The `fullname` function returns the pathname relative to the project root for each of the files or directories.

### 9.1.9 absname

       $(absname files) : String Sequence
          files : File Sequence

The `absname` function returns the absolute pathname for each of the files or directories.

### 9.1.10 homename

       $(homename files) : String Sequence
          files : File Sequence

The `homename` function returns the name of a file in tilde form, if possible. The unexpanded forms are computed lazily: the `homename` function will usually evaluate to an absolute pathname until the first tilde-expansion for the same directory.

### 9.1.11 suffix

       $(suffix files) : String Sequence
          files : StringSequence

The `suffix` function returns the suffixes for a list of files. If a file has no suffix, the function returns the empty string.

For example, the expression `$(suffix dir1/dir2/a.out /etc/a /foo.ml)` evaluates to `.out .ml`.

## 9.2 Path search

### 9.2.1 which

       $(which files) : File Sequence
          files : String Sequence

The `which` function searches for executables in the current command search path, and returns `file` values for each of the commands. It is an error if a command is not found.

### 9.2.2 where

The `where` function is similar to which, except it returns the list of all the locations of the given executable (in the order in which the corresponding directories appear in `$PATH`). In case a command is handled internally by the `Shell` object, the first string in the output will describe the command as a built-in function.

        % where echo
        echo is a Shell object method (a built-in function)
        /bin/echo

### 9.2.3 rehash

        rehash()

The `rehash` function resets all search paths.

### 9.2.4 exists-in-path

       $(exists-in-path files) : String
          files : String Sequence

The `exists-in-path` function tests whether all executables are present in the current search path.

### 9.2.5 digest

         $(digest files) : String Array
            file : File Array
         raises RuntimeException

         $(digest-optional files) : String Array
            file : File Array

The `digest` and `digest-optional` functions compute MD5 digests of files. The `digest` function raises an exception if a file does no exist. The `digest-optional` returns `false` if a file does no exist. MD5 digests are cached.

### 9.2.6 find-in-path

        $(find-in-path path, files) : File Array
           path : Dir Array
           files : String Array
        raises RuntimeException

        $(find-in-path-optional path, files) : File Array

The `find-in-path` function searches for the files in a search path. Only the tail of the filename is significant. The `find-in-path` function raises an exception if the file can't be found. The `find-in-path-optional` function silently removes files that can't be found.

### 9.2.7 digest-path

        $(digest-in-path path, files) : String/File Array
           path : Dir Array
           files : String Array
        raises RuntimeException

        $(digest-in-path-optional path, files) : String/File Array

The `digest-in-path` function searches for the files in a search path and returns the file and digest for each file. Only the tail of the filename is significant. The `digest-in-path` function raises an exception if the file can't be found. The `digest-in-path-optional` function silently removes elements that can't be found.

## 9.3 File stats

### 9.3.1 file-exists, target-exists, target-is-proper

       $(file-exists files) : String
       $(target-exists files) : String
       $(target-is-proper files) : String
           files : File Sequence

The `file-exists` function checks whether the files listed exist. The `target-exists` function is similar to the `file-exists` function. However, it returns true if the file exists or if it can be built by the current project. The `target-is-proper` returns true only if the file can be generated in the current project.

### 9.3.2 stat-reset

       $(stat-reset files) : String
           files : File Sequence

OMake uses a stat-cache. The `stat-reset` function reset the `stat` information for the given files, forcing the `stat` information to be recomputed the next time it is requested.

### 9.3.3 filter-exists, filter-targets, filter-proper-targets

       $(filter-exists files) : File Sequence
       $(filter-targets files) : File Sequence
       $(filter-proper-targets) : File Sequence
          files : File Sequence

The `filter-exists`, `filter-targets`, and `filter-proper-targets` functions remove files from a list of files.

- `filter-exists`: the result is the list of files that exist.
- `filter-targets`: the result is the list of files either exist, or can be built by the current project.
- `filter-proper-targets`: the result is the list of files that can be built in the current project.

One way to create a simple “clean” rule that removes generated files from the project is by removing all files that can be built in the current project. CAUTION: you should be careful before you do this. The rule removes any file that can potentially be reconstructed. There is no check to make sure that the commands to rebuild the file would actually succeed. Also, note that no file outside the current project will be deleted.

        .PHONY: clean

        clean:
            rm $(filter-proper-targets $(ls R, .))

See the `dependencies-proper` function to see an alternate method for removing intermediate files.

If you use CVS, you may wish to use the `cvs_realclean` program that is distributed with `omake`.

### 9.3.4 find-targets-in-path, find-targets-in-path-optional

        $(find-targets-in-path path files) : File Array
        $(find-targets-in-path-optional path, files) : File Array
            path : Dir Array
            files : File Sequence

The `find-target-in-path` function searches for targets in the search path. For each file `file` in the file list, the path is searched sequentially for a directory `dir` such that the target `dir/file` exists. If so, the file `dir/file` is returned.

For example, suppose you are building a C project, and project contains a subdirectory `src/` containing only the files `fee.c` and `foo.c`. The following expression evaluates to the files `src/fee.o` `src/foo.o` even if the files have not already been built.

        $(find-targets-in-path lib src, fee.o foo.o)

        # Evaluates to
        src/fee.o src/foo.o

The `find-targets-in-path` function raises an exception if the file can't be found. The `find-targets-in-path-optional` function silently removes targets that can't be found.

        $(find-targets-in-path-optional lib src, fee.o foo.o fum.o)

        # Evaluates to
        src/fee.o src/foo.o

### 9.3.5 file-sort

       $(file-sort order, files) : File Sequence
          order : String
          files : File Sequence

The `file-sort` function sorts a list of filenames by build order augmented by a set of sort rules. Sort rules are declared using the `.ORDER` target. The `.BUILDORDER` defines the default order.

`$(file-sort <order>, <files>)`

For example, suppose we have the following set of rules.

       a: b c
       b: d
       c: d

       .DEFAULT: a b c d
          echo $(file-sort .BUILDORDER, a b c d)

In the case, the sorter produces the result `d b c a`. That is, a target is sorted after its dependencies. The sorter is frequently used to sort files that are to be linked by their dependencies (for languages where this matters).

There are three important restrictions to the sorter:

- The sorter can be used only within a rule body. The reason for this is that all dependencies must be known before the sort is performed.
- The sorter can only sort files that are buildable in the current project.
- The sorter will fail if the dependencies are cyclic.

#### 9.3.5.1 sort rule

It is possible to further constrain the sorter through the use of sort rules. A sort rule is declared in two steps. The target must be listed as an `.ORDER` target; and then a set of sort rules must be given. A sort rule defines a pattern constraint.

       .ORDER: .MYORDER

       .MYORDER: %.foo: %.bar
       .MYORDER: %.bar: %.baz

       .DEFAULT: a.foo b.bar c.baz d.baz
          echo $(sort .MYORDER, a.foo b.bar c.baz d.baz)

In this example, the `.MYORDER` sort rule specifies that any file with a suffix `.foo` should be placed after any file with suffix `.bar`, and any file with suffix `.bar` should be placed after a file with suffix `.baz`.

In this example, the result of the sort is `d.baz c.baz b.bar a.foo`.

### 9.3.6 file-check-sort

       file-check-sort(files)
          files : File Sequence
       raises RuntimeException

The `file-check-sort` function checks whether a list of files is in sort order. If so, the list is returned unchanged. If not, the function raises an exception.

`$(file-check-sort <order>, <files>)`

## 9.4 Globbing and file listings

OMake commands are “glob-expanded” before being executed. That is, names may contain patterns that are expanded to sequences of file and directory names. The syntax follows the standard bash(1), csh(1), syntax, with the following rules.

- A pathname is a sequence of directory and file names separated by one of the `/` or `\` characters. For example, the following pathnames refer to the same file: `/home/jyh/OMakefile` and `/home\jyh/OMakefile`.
- Glob-expansion is performed on the components of a path. If a path contains occurrences of special characters (listed below), the path is viewed as a pattern to be matched against the actual files in the system. The expansion produces a sequence of all file/directory names that match.

  For the following examples, suppose that a directory `/dir` contains files named `a`, `-a`, `a.b`, and `b.c`.

  `*`
    Matches any sequence of zero-or-more characters. For example, the pattern `/dir/a*` expands to `/dir/a /dir/aa /dir/a.b`.
  `?`
    Matches exactly one character. The pattern `/dir/?a` expands the filename `/dir/-a`.
  `[...]`
    Square brackets denote character sets and ranges in the ASCII character set. The pattern may contain individual characters c or character ranges `c1-c2`. The pattern matches any of the individual characters specified, or any characters in the range. A leading “hat” inverts the send of the pattern. To specify a pattern that contains the literal characters `-`, the `-` should occur as the first character in the range.

    Pattern | Expansion
    `/dir/[a-b]*` | `/dir/a /dir/a.b /dir/b.c`
    `/dir/[-a-b]*` | `/dir/a /dir/-a /dir/a.b /dir/b.c`
    `/dir/[-a]*` | `/dir/a /dir/-a /dir/a.b`

  `{s1,...,sN}`
    Braces indicate brace-expansion. The braces delimit a sequence of strings separated by commas. Given N strings, the result produces N copies of the pattern, one for each of the strings si.

    Pattern | Expansion
    `a{b,c,d}` | `ab ac ad`
    `a{b{c,d},e}` | `abc abd ae`
    `a{?{[A-Z],d},*}` | `a?[A-Z] a?d a*`

  ``
    The tilde is used to specify home directories. Depending on your system, these might be possible expansions.

    Pattern | Expansion
    `~jyh` | `/home/jyh`
    `~bob/*.c` | `c:\Documents and Settings\users\bob`

    The `\` character is both a pathname separator and an escape character. If followed by a special glob character, the `\` changes the sense of the following character to non-special status. Otherwise, `\` is viewed as a pathname separator.

    Pattern | Expansion
    `~jyh/\*` | `~jyh/*` (`*` is literal)
    `/dir/\[a-z?` | `/dir/[a-z?` (`[` is literal, `?` is a pattern).
    `c:\Program Files\[A-z]` | `c:\Program Files[A-z]*`

    Note that the final case might be considered to be ambiguous (where `\` should be viewed as a pathname separator, not as an escape for the subsequent `[` character. If you want to avoid this ambiguity on Win32, you should use the forward slash `/` even for Win32 pathnames (the `/` is translated to `\` in the output).

    Pattern | Expansion
    `c:/Program Files/[A-z]*` | `c:\Program Files\WindowsUpdate ...`

### 9.4.1 glob

       $(glob strings) : Node Array
          strings : String Sequence
       $(glob options, strings) : Node Array
          options : String
          strings : String Sequence

The `glob` function performs glob-expansion.

The . and .. entries are always ignored.

The options are:

b
  Do not perform `csh`(1)-style brace expansion.
e
  The `\` character does not escape special characters.
n
  If an expansion fails, return the expansion literally instead of aborting.
i
  If an expansion fails, it expands to nothing.
.
  Allow wildcard patterns to match files beginning with a .
A
  Return all files, including files that begin with a .
F
  Match only normal files (any file that is not a directory).
D
  Match only directory files.
C
  Ignore files according to `cvs`(1) rules.
P
  Include only proper subdirectories.

In addition, the following variables may be defined that affect the behavior of `glob`.

GLOB_OPTIONS
  A string containing default options.
GLOB_IGNORE
  A list of shell patterns for filenames that `glob` should ignore.
GLOB_ALLOW
  A list of shell patterns. If a file does not match a pattern in `GLOB_ALLOW`, it is ignored.

The returned files are sorted by name.

### 9.4.2 ls

       $(ls files) : Node Array
          files : String Sequence
       $(ls options, files) : Node Array
          files : String Sequence

The `ls` function returns the filenames in a directory.

The . and .. entries are always ignored. The patterns are shell-style patterns, and are glob-expanded.

The options include all of the options to the `glob` function, plus the following.

R
  Perform a recursive listing.

The `GLOB_ALLOW` and `GLOB_IGNORE` variables can be defined to control the globbing behavior. The returned files are sorted by name.

### 9.4.3 subdirs

       $(subdirs dirs) : Dir Array
          dirs : String Sequence
       $(subdirs options, dirs) : Dir Array
          options : String
          dirs : String Sequence

The `subdirs` function returns all the subdirectories of a list of directories, recursively.

The possible options are the following:

A
  Return directories that begin with a .
C
  Ignore files according to `.cvsignore` rules.
P
  Include only proper subdirectories.

## 9.5 Filesystem operations

### 9.5.1 mkdir

       mkdir(mode, node...)
          mode : Int
          node : Node
       raises RuntimeException

       mkdir(node...)
          node : Node
       raises RuntimeException

The `mkdir` function creates a directory, or a set of directories. The following options are supported.

-m mode
  Specify the permissions of the created directory.
-p
  Create parent directories if they do not exist.
–
  Interpret the remaining names literally.

### 9.5.2 Stat

The `Stat` object represents an information about a filesystem node, as returned by the `stat` and `lstat` functions. It contains the following fields.

dev
  : the device number.
ino
  : the inode number.
kind
  : the kind of the file, one of the following: `REG` (regular file), `DIR` (directory), `CHR` (character device), `BLK` (block device), `LNK` (symbolic link), `FIFO` (named pipe), `SOCK` (socket).
perm
  : access rights, represented as an integer.
nlink
  : number of links.
uid
  : user id of the owner.
gid
  : group id of the file's group.
rdev
  : device minor number.
size
  : size in bytes.
atime
  : last access time, as a floating point number.
mtime
  : last modification time, as a floating point number.
ctime
  : last status change time, as a floating point number.

Not all of the fields will have meaning on all operating systems.

### 9.5.3 stat, lstat

        $(stat node...) : Stat
           node : Node or Channel
        $(lstat node...) : Stat
           node : Node or Channel
        raises RuntimeException

The `stat` functions return file information. If the file is a symbolic link, the `stat` function refers to the destination of the link; the `lstat` function refers to the link itself.

### 9.5.4 unlink

       $(unlink file...)
          file : File
       #(rm file...)
          file : File
       $(rmdir dir...)
          dir : Dir
       raises RuntimeException

The `unlink` and `rm` functions remove a file. The `rmdir` function removes a directory.

The following options are supported for `rm` and `rmdir`.

-f
  ignore nonexistent files, never prompt.
-i
  prompt before removal.
-r
  remove the contents of directories recursively.
-v
  explain what is going on.
–
  the rest of the values are interpreted literally.

### 9.5.5 rename

        rename(old, new)
           old : Node
           new : Node
        mv(nodes... dir)
           nodes : Node Sequence
           dir   : Dir
        cp(nodes... dir)
           nodes : Node Sequence
           dir   : Dir
        raises RuntimeException

The `rename` function changes the name of a file or directory named `old` to `new`.

The `mv` function is similar, but if `new` is a directory, and it exists, then the files specified by the sequence are moved into the directory. If not, the behavior of `mv` is identical to `rename`. The `cp` function is similar, but the original file is not removed.

The `mv` and `cp` functions take the following options.

-f
  Do not prompt before overwriting.
-i
  Prompt before overwriting.
-v
  Explain what it happening.
-r
  Copy the contents of directories recursively.
–
  Interpret the remaining arguments literally.

### 9.5.6 link

       link(src, dst)
          src : Node
          dst : Node
       raises RuntimeException

The `link` function creates a hard link named `dst` to the file or directory `src`.

Hard links may work under Win32 when NTFS is used.

Normally, only the superuser can create hard links to directories.

### 9.5.7 symlink

       symlink(src, dst)
          src : Node
          dst : Node
       raises RuntimeException

The `symlink` function creates a symbolic link `dst` that points to the `src` file.

The link name is computed relative to the target directory. For example, the expression `$(symlink a/b, c/d)` creates a link named `c/d -> ../a/b`.

Symbolic links are not supported in Win32. Consider using the `ln-or-cp` `Shell` alias for cross-platform portable linking/copying.

### 9.5.8 readlink

       $(readlink node...) : Node
          node : Node

The `readlink` function reads the value of a symbolic link.

### 9.5.9 chmod

       chmod(mode, dst...)
          mode : Int
          dst : Node or Channel
       chmod(mode dst...)
          mode : String
          dst : Node Sequence
       raises RuntimeException

The `chmod` function changes the permissions of the targets.

Options:

-v
  Explain what is happening.
-r
  Change files and directories recursively.
-f
  Continue on errors.
–
  Interpret the remaining argument literally.

### 9.5.10 chown

       chown(uid, gid, node...)
          uid : Int
          gid : Int
          node : Node or Channel
       chown(uid, node...)
          uid : Int
          node : Node or Channel
       raises RuntimeException

The `chown` function changes the user and group id of the file. If the `gid` is not specified, it is not changed. If either id is -1, that id is not changed.

### 9.5.11 truncate

       truncate(length, node...)
           length : Int
           node : Node or Channel
       raises RuntimeException

The `truncate` function truncates a file to the given length.

### 9.5.12 umask

        $(umask mode) : Int
           mode : Int
        raises RuntimeException

Sets the file mode creation mask. The previous mask is returned. This value is not scoped, changes have global effect.

## 9.6 vmount

### 9.6.1 vmount

        vmount(src, dst)
           src, dst : Dir
        vmount(flags, src, dst)
           flags : String
           src, dst : Dir

“Mount” the `src` directory on the `dst` directory. This is a virtual mount, changing the behavior of the `$(file ...)` function. When the `$(file str)` function is used, the resulting file is taken relative to the `src` directory if the file exists. Otherwise, the file is relative to the current directory.

The main purpose of the `vmount` function is to support multiple builds with separate configurations or architectures.

The options are as follows.

l
  Create symbolic links to files in the `src` directory.
c
  Copy files from the `src` directory.

Mount operations are scoped.

### 9.6.2 add-project-directories

        add-project-directories(dirs)
           dirs : Dir Array

Add the directories to the set of directories that omake considers to be part of the project. This is mainly used to avoid omake complaining that the current directory is not part of the project.

### 9.6.3 remove-project-directories

        remove-project-directories(dirs)
           dirs : Dir Array

Removed the directories from the set of directories that omake considers to be part of the project. This is mainly used to cancel a `.SUBDIRS` from including a directory if it is determined that the directory does not need to be compiled.

## 9.7 File predicates

### 9.7.1 test

       test(exp) : Bool
          exp : String Sequence

The expression grammar is as follows:

- `!` expression : expression is not true
- expression1 `-a` expression2 : both expressions are true
- expression1 `-o` expression2 : at least one expression is true
- `(` expression `)` : expression is true

The base expressions are:

- `-n` string : The string has nonzero length
- `-z` string : The string has zero length
- string `=` string : The strings are equal
- string `!=` string : The strings are not equal
- int1 `-eq` int2 : The integers are equal
- int1 `-ne` int2 : The integers are not equal
- int1 `-gt` int2 : int1 is larger than int2
- int1 `-ge` int2 : int2 is not larger than int1
- int1 `-lt` int2 : int1 is smaller than int2
- int1 `-le` int2 : int1 is not larger than int2
- file1 `-ef` file2 : On Unix, file1 and file2 have the same device and inode number. On Win32, file1 and file2 have the same name.
- file1 `-nt` file2 : file1 is newer than file2
- file1 `-ot` file2 : file1 is older than file2
- `-b` file : The file is a block special file
- `-c` file : The file is a character special file
- `-d` file : The file is a directory
- `-e` file : The file exists
- `-f` file : The file is a normal file
- `-g` file : The set`-group-id` bit is set on the file
- `-G` file : The file's group is the current effective group
- `-h` file : The file is a symbolic link (also `-L`)
- `-k` file : The file's sticky bit is set
- `-L` file : The file is a symbolic link (also `-h`)
- `-O` file : The file's owner is the current effective user
- `-p` file : The file is a named pipe
- `-r` file : The file is readable
- `-s` file : The file is empty
- `-S` file : The file is a socket
- `-u` file : The set`-user-id` bit is set on the file
- `-w` file : The file is writable
- `-x` file : The file is executable

A string is any sequence of characters; leading `-` characters are allowed.

An int is a string that can be interpreted as an integer. Unlike traditional versions of the test program, the leading characters may specify an arity. The prefix `0b` means the numbers is in binary; the prefix `0o` means the number is in octal; the prefix `0x` means the number is in hexadecimal. An int can also be specified as `-l` string, which evaluates to the length of the string.

A file is a string that represents the name of a file.

The syntax mirrors that of the `test`(1) program. If you are on a Unix system, the man page explains more. Here are some examples.

        # Create an empty file
        osh> touch foo
        # Is the file empty?
        osh> test(-e foo)
        - : true
        osh> test(! -e foo)
        - : false
        # Create another file
        osh> touch boo
        # Is the newer file newer?
        osh> test(boo -nt foo)
        - : true
        # A more complex query
        # boo is newer than foo, and foo is empty
        osh> test(\( boo -nt foo \) -a -e foo)
        - : true

### 9.7.2 find

       find(exp) : Node Array
          exp : String Sequence

The `find` function searches a directory recursively, returning the files for which the expression evaluates to true.

The expression argument uses the same syntax as the `test` function, with the following exceptions.

1. The expression may begin with a directory. If not specified, the current directory is searched.
2. The `{}` string expands to the current file being examined.

The syntax of the expression is the same as `test`, with the following additions.

- `-name` string : The current file matches the glob expression (see Section 9.4).

The `find` function performs a recursive scan of all subdirectories. The following call is being run from the root of the `omake` source directory.

        osh> find(. -name fo* )
        - : <array
                /home/jyh/.../omake/mk/.svn/format
                /home/jyh/.../omake/RPM/.svn/format
                ...
                /home/jyh/.../omake/osx_resources/installer_files/.svn/format>

Another example, listing only those files that are normal files or symbolic links.

        osh> find(. -name fo* -a \( -f {} -o -L {} \))
        - : <array
                /home/jyh/.../omake/mk/.svn/format
                /home/jyh/.../omake/RPM/.svn/format
                ...
                /home/jyh/.../omake/osx_resources/installer_files/.svn/format>

## 9.8 IO functions

### 9.8.1 Standard channels

The following variables define the standard channels.

##### stdin

    stdin : InChannel

The standard input channel, open for reading.

##### stdout

    stdout : OutChannel

The standard output channel, open for writing.

##### stderr

    stderr : OutChannel

The standard error channel, open for writing.

### 9.8.2 open-in-string

The `open-in-string` treats a string as if it were a file and returns a channel for reading.

       $(open-in-string s) : Channel
           s : String

### 9.8.3 open-out-string, out-string

The `open-out-string` creates a channel that writes to a string instead of a file. The string may be retrieved with the `out-string` function.

       $(open-out-string) : Channel
       $(out-string chan) : String
           chan : OutChannel

### 9.8.4 fopen

The `fopen` function opens a file for reading or writing.

       $(fopen file, mode) : Channel
          file : File
          mode : String

The `file` is the name of the file to be opened. The `mode` is a combination of the following characters.

r
  Open the file for reading; it is an error if the file does not exist.
w
  Open the file for writing; the file is created if it does not exist.
a
  Open the file in append mode; the file is created if it does not exist.
+
  Open the file for both reading an writing.
t
  Open the file in text mode (default).
b
  Open the file in binary mode.
n
  Open the file in nonblocking mode.
x
  Fail if the file already exists.

Binary mode is not significant on Unix systems, where text and binary modes are equivalent.

### 9.8.5 close

        $(close channel...)
           channel : Channel

The `close` function closes a file that was previously opened with `fopen`.

### 9.8.6 read

       $(read channel, amount) : String
          channel : InChannel
          amount  : Int
       raises RuntimeException

The `read` function reads up to `amount` bytes from an input channel, and returns the data that was read. If an end-of-file condition is reached, the function raises a `RuntimeException` exception.

### 9.8.7 write

       $(write channel, buffer, offset, amount) : String
          channel : OutChannel
          buffer  : String
          offset  : Int
          amount  : Int
       $(write channel, buffer) : String
          channel : OutChannel
          buffer  : String
       raises RuntimeException

In the 4-argument form, the `write` function writes bytes to the output channel `channel` from the `buffer`, starting at position `offset`. Up to `amount` bytes are written. The function returns the number of bytes that were written.

The 3-argument form is similar, but the `offset` is 0.

In the 2-argument form, the `offset` is 0, and the `amount` if the length of the `buffer`.

If an end-of-file condition is reached, the function raises a `RuntimeException` exception.

### 9.8.8 lseek

        $(lseek channel, offset, whence) : Int
           channel : Channel
           offset  : Int
           whence  : String
        raises RuntimeException

The `lseek` function repositions the offset of the channel `channel` according to the `whence` directive, as follows:

SEEK_SET
  The offset is set to `offset`.
SEEK_CUR
  The offset is set to its current position plus `offset` bytes.
SEEK_END
  The offset is set to the size of the file plus `offset` bytes.

The `lseek` function returns the new position in the file.

### 9.8.9 rewind

       rewind(channel...)
          channel : Channel

The `rewind` function set the current file position to the beginning of the file.

### 9.8.10 tell

        $(tell channel...) : Int...
           channel : Channel
        raises RuntimeException

The `tell` function returns the current position of the `channel`.

### 9.8.11 flush

       $(flush channel...)
          channel : OutChannel

The `flush` function can be used only on files that are open for writing. It flushes all pending data to the file.

### 9.8.12 dup

        $(dup channel) : Channel
           channel : Channel
        raises RuntimeException

The `dup` function returns a new channel referencing the same file as the argument.

### 9.8.13 dup2

       dup2(channel1, channel2)
          channel1 : Channel
          channel2 : Channel
       raises RuntimeException

The `dup2` function causes `channel2` to refer to the same file as `channel1`.

### 9.8.14 set-nonblock

       set-nonblock-mode(mode, channel...)
          channel : Channel
          mode : String

The `set-nonblock-mode` function sets the nonblocking flag on the given channel. When IO is performed on the channel, and the operation cannot be completed immediately, the operations raises a `RuntimeException`.

### 9.8.15 set-close-on-exec-mode

       set-close-on-exec-mode(mode, channel...)
          channel : Channel
          mode : String
       raises RuntimeException

The `set-close-on-exec-mode` function sets the close-on-exec flags for the given channels. If the close-on-exec flag is set, the channel is not inherited by child processes. Otherwise it is.

### 9.8.16 pipe

       $(pipe) : Pipe
       raises RuntimeException

The `pipe` function creates a `Pipe` object, which has two fields. The `read` field is a channel that is opened for reading, and the `write` field is a channel that is opened for writing.

### 9.8.17 mkfifo

       mkfifo(mode, node...)
          mode : Int
          node : Node

The `mkfifo` function creates a named pipe.

### 9.8.18 select

       $(select rfd..., wfd..., wfd..., timeout) : Select
          rfd : InChannel
          wfd : OutChannel
          efd : Channel
          timeout : float
       raises RuntimeException

The `select` function polls for possible IO on a set of channels. The `rfd` are a sequence of channels for reading, `wfd` are a sequence of channels for writing, and `efd` are a sequence of channels to poll for error conditions. The `timeout` specifies the maximum amount of time to wait for events.

On successful return, `select` returns a `Select` object, which has the following fields:

read
  An array of channels available for reading.
write
  An array of channels available for writing.
error
  An array of channels on which an error has occurred.

### 9.8.19 lockf

        lockf(channel, command, len)
           channel : Channel
           command : String
           len : Int
        raises RuntimeException

The `lockf` function places a lock on a region of the channel. The region starts at the current position and extends for `len` bytes.

The possible values for `command` are the following.

F_ULOCK
  Unlock a region.
F_LOCK
  Lock a region for writing; block if already locked.
F_TLOCK
  Lock a region for writing; fail if already locked.
F_TEST
  Test a region for other locks.
F_RLOCK
  Lock a region for reading; block if already locked.
F_TRLOCK
  Lock a region for reading; fail is already locked.

### 9.8.20 InetAddr

The `InetAddr` object describes an Internet address. It contains the following fields.

addr
  `String`: the Internet address.
port
  `Int`: the port number.

### 9.8.21 Host

A `Host` object contains the following fields.

name
  `String`: the name of the host.
aliases
  `String Array`: other names by which the host is known.
addrtype
  `String`: the preferred socket domain.
addrs
  `InetAddr Array`: an array of Internet addresses belonging to the host.

### 9.8.22 gethostbyname

       $(gethostbyname host...) : Host...
          host : String
       raises RuntimeException

The `gethostbyname` function returns a `Host` object for the specified host. The `host` may specify a domain name or an Internet address.

### 9.8.23 Protocol

The `Protocol` object represents a protocol entry. It has the following fields.

name
  `String`: the canonical name of the protocol.
aliases
  `String Array`: aliases for the protocol.
proto
  `Int`: the protocol number.

### 9.8.24 getprotobyname

       $(getprotobyname name...) : Protocol...
          name : Int or String
       raises RuntimeException

The `getprotobyname` function returns a `Protocol` object for the specified protocol. The `name` may be a protocol name, or a protocol number.

### 9.8.25 Service

The `Service` object represents a network service. It has the following fields.

name
  `String`: the name of the service.
aliases
  `String Array`: aliases for the service.
port
  `Int`: the port number of the service.
proto
  `Protocol`: the protocol for the service.

### 9.8.26 getservbyname

       $(getservbyname service...) : Service...
          service : String or Int
       raises RuntimeException

The `getservbyname` function gets the information for a network service. The `service` may be specified as a service name or number.

### 9.8.27 socket

       $(socket domain, type, protocol) : Channel
          domain : String
          type : String
          protocol : String
       raises RuntimeException

The `socket` function creates an unbound socket.

The possible values for the arguments are as follows.

The `domain` may have the following values.

PF_UNIX or unix
  Unix domain, available only on Unix systems.
PF_INET or inet
  Internet domain, IPv4.
PF_INET6 or inet6
  Internet domain, IPv6.

The `type` may have the following values.

SOCK_STREAM or stream
  Stream socket.
SOCK_DGRAM or dgram
  Datagram socket.
SOCK_RAW or raw
  Raw socket.
SOCK_SEQPACKET or seqpacket
  Sequenced packets socket

The `protocol` is an `Int` or `String` that specifies a protocol in the protocols database.

### 9.8.28 bind

       bind(socket, host, port)
          socket : InOutChannel
          host : String
          port : Int
       bind(socket, file)
          socket : InOutChannel
          file : File
       raise RuntimeException

The `bind` function binds a socket to an address.

The 3-argument form specifies an Internet connection, the `host` specifies a host name or IP address, and the `port` is a port number.

The 2-argument form is for `Unix` sockets. The `file` specifies the filename for the address.

### 9.8.29 listen

       listen(socket, requests)
          socket : InOutChannel
          requests : Int
       raises RuntimeException

The `listen` function sets up the socket for receiving up to `requests` number of pending connection requests.

### 9.8.30 accept

       $(accept socket) : InOutChannel
          socket : InOutChannel
       raises RuntimeException

The `accept` function accepts a connection on a socket.

### 9.8.31 connect

        connect(socket, addr, port)
           socket : InOutChannel
           addr : String
           port : int
        connect(socket, name)
           socket : InOutChannel
           name : File
        raise RuntimeException

The `connect` function connects a socket to a remote address.

The 3-argument form specifies an Internet connection. The `addr` argument is the Internet address of the remote host, specified as a domain name or IP address. The `port` argument is the port number.

The 2-argument form is for Unix sockets. The `name` argument is the filename of the socket.

### 9.8.32 getchar

        $(getc) : String
        $(getc file) : String
           file : InChannel or File
        raises RuntimeException

The `getc` function returns the next character of a file. If the argument is not specified, `stdin` is used as input. If the end of file has been reached, the function returns `false`.

### 9.8.33 gets

       $(gets) : String
       $(gets channel) : String
          channel : InChannel or File
       raises RuntimeException

The `gets` function returns the next line from a file. The function returns the empty string if the end of file has been reached. The line terminator is removed.

### 9.8.34 fgets

       $(fgets) : String
       $(fgets channel) : String
          channel : InChannel or File
       raises RuntimeException

The `fgets` function returns the next line from a file that has been opened for reading with `fopen`. The function returns the empty string if the end of file has been reached. The returned string is returned as literal data. The line terminator is not removed.

## 9.9 Printing functions

Output is printed with the `print` and `println` functions. The `println` function adds a terminating newline to the value being printed, the `print` function does not.

        fprint(<file>, <string>)
        print(<string>)
        eprint(<string>)
        fprintln(<file>, <string>)
        println(<string>)
        eprintln(<string>)

The `fprint` functions print to a file that has been previously opened with `fopen`. The `print` functions print to the standard output channel, and the `eprint` functions print to the standard error channel.

## 9.10 Value printing functions

Values can be printed with the `printv` and `printvln` functions. The `printvln` function adds a terminating newline to the value being printed, the `printv` function does not.

        fprintv(<file>, <string>)
        printv(<string>)
        eprintv(<string>)
        fprintvln(<file>, <string>)
        printvln(<string>)
        eprintvln(<string>)

The `fprintv` functions print to a file that has been previously opened with `fopen`. The `printv` functions print to the standard output channel, and the `eprintv` functions print to the standard error channel.

## 9.11 Higher-level IO functions

### 9.11.1 Regular expressions

Many of the higher-level functions use regular expressions. Regular expressions are defined by strings with syntax nearly identical to `awk`(1).

Strings may contain the following character constants.

- `\\` : a literal backslash.
- `\a` : the alert character `^G`.
- `\b` : the backspace character `^H`.
- `\f` : the formfeed character `^L`.
- `\n` : the newline character `^J`.
- `\r` : the carriage return character `^M`.
- `\t` : the tab character `^I`.
- `\v` : the vertical tab character.
- `\xhh...` : the character represented by the string of hexadecimal digits `h`. All valid hexadecimal digits following the sequence are considered to be part of the sequence.
- `\ddd` : the character represented by 1, 2, or 3 octal digits.

Regular expressions are defined using the special characters `.\^$[(){}*?`+.

- `c` : matches the literal character `c` if `c` is not a special character.
- `\c` : matches the literal character `c`, even if `c` is a special character.
- `.` : matches any character, including newline.
- `^` : matches the beginning of a line.
- `$` : matches the end of line.
- `[abc...]` : matches any of the characters `abc...`
- `[^abc...]` : matches any character except `abc...`
- `r1|r2` : matches either `r1` or `r2`.
- `r1r2` : matches `r1` and then `r2`.
- `r`+ : matches one or more occurrences of `r`.
- `r*` : matches zero or more occurrences of `r`.
- `r?` : matches zero or one occurrence of `r`.
- `(r)` : parentheses are used for grouping; matches `r`.
- `\(r\)` : also defines grouping, but the expression matched within the parentheses is available to the output processor through one of the variables `$1`, `$2`, ...
- `r{n}` : matches exactly `n` occurrences of `r`.
- `r{n,}` : matches `n` or more occurrences of `r`.
- `r{n,m}` : matches at least `n` occurrences of `r`, and no more than `m` occurrences.
- `\y`: matches the empty string at either the beginning or end of a word.
- `\B`: matches the empty string within a word.
- `\<`: matches the empty string at the beginning of a word.
- `\>`: matches the empty string at the end of a word.
- `\w`: matches any character in a word.
- `\W`: matches any character that does not occur within a word.
- `\``: matches the empty string at the beginning of a file.
- `\'`: matches the empty string at the end of a file.

Character classes can be used to specify character sequences abstractly. Some of these sequences can change depending on your LOCALE.

- `[:alnum:]` Alphanumeric characters.
- `[:alpha:]` Alphabetic characters.
- `[:lower:]` Lowercase alphabetic characters.
- `[:upper:]` Uppercase alphabetic characters.
- `[:cntrl:]` Control characters.
- `[:digit:]` Numeric characters.
- `[:xdigit:]` Numeric and hexadecimal characters.
- `[:graph:]` Characters that are printable and visible.
- `[:print:]` Characters that are printable, whether they are visible or not.
- `[:punct:]` Punctuation characters.
- `[:blank:]` Space or tab characters.
- `[:space:]` Whitespace characters.

### 9.11.2 cat

        cat(files) : Sequence
           files : File or InChannel Sequence

The `cat` function concatenates the output from multiple files and returns it as a string.

### 9.11.3 grep

       grep(pattern) : String  # input from stdin, default options
          pattern : String
       grep(pattern, files) : String  # default options
          pattern : String
          files   : File Sequence
       grep(options, pattern, files) : String
         options : String
         pattern : String
         files   : File Sequence

The `grep` function searches for occurrences of a regular expression `pattern` in a set of files, and prints lines that match. This is like a highly-simplified version of `grep`(1).

The options are:

q
  If specified, the output from `grep` is not displayed.
h
  If specified, output lines will not include the filename (default, when only one input file is given).
n
  If specified, output lines include the filename (default, when more than one input file is given).
v
  If specified, search for lines without a match instead of lines with a match,

The `pattern` is a regular expression.

If successful (`grep` found a match), the function returns `true`. Otherwise, it returns `false`.

### 9.11.4 scan

       scan(input-files)
       case string1
          body1
       case string2
          body2
       ...
       default
          bodyd

The `scan` function provides input processing in command-line form. The function takes file/filename arguments. If called with no arguments, the input is taken from `stdin`. If arguments are provided, each specifies an `InChannel`, or the name of a file for input. Output is always to `stdout`.

The `scan` function operates by reading the input one line at a time, and processing it according to the following algorithm.

For each line, the record is first split into fields, and the fields are bound to the variables `$1, $2, ...`. The variable `$0` is defined to be the entire line, and `$*` is an array of all the field values. The `$(NF)` variable is defined to be the number of fields.

Next, a case expression is selected. If `string_i` matches the token `$1`, then `body_i` is evaluated. If the body ends in an `export`, the state is passed to the next clause. Otherwise the value is discarded.

For example, here is an `scan` function that acts as a simple command processor.

        calc() =
           i = 0
           scan(script.in)
           case print
              println($i)
           case inc
              i = $(add $i, 1)
              export
           case dec
              i = $(sub $i, 1)
              export
           case addconst
              i = $(add $i, $2)
              export
           default
              eprintln($"Unknown command: $1")

The `scan` function also supports several options.

        scan(options, files)
        ...

A
  Parse each line as an argument list, where arguments may be quoted. For example, the following line has three words, “`ls`”, “`-l`”, “`Program Files`”.

             ls -l "Program Files"

O
  Parse each line using white space as the separator, using the usual OMake algorithm for string parsing. This is the default.
x
  Once each line is split, reduce each word using the hex representation. This is the usual hex representation used in URL specifiers, so the string “Program Files” may be alternately represented in the form ProgramProgram+Files.

Note, if you want to redirect the output to a file, the easiest way is to redefine the `stdout` variable. The `stdout` variable is scoped the same way as other variables, so this definition does not affect the meaning of `stdout` outside the `calc` function.

        calc() =
            stdout = $(fopen script.out, w)
            scan(script.in)
               ...
            close(stdout)

### 9.11.5 awk

       awk(input-files)
       case pattern1:
          body1
       case pattern2:
          body2
       ...
       default:
          bodyd

or

       awk(options, input-files)
       case pattern1:
          body1
       case pattern2:
          body2
       ...
       default:
          bodyd

The `awk` function provides input processing similar to `awk`(1), but more limited. The `input-files` argument is a sequence of values, each specifies an `InChannel`, or the name of a file for input. If called with no options and no file arguments, the input is taken from `stdin`. Output is always to `stdout`.

The variables `RS` and `FS` define record and field separators as regular expressions. The default value of `RS` is the regular expression `\r|\n|\r\n`. The default value of `FS` is the regular expression `[ \t]`+.

The `awk` function operates by reading the input one record at a time, and processing it according to the following algorithm.

For each line, the record is first split into fields using the field separator `FS`, and the fields are bound to the variables `$1, $2, ...`. The variable `$0` is defined to be the entire line, and `$*` is an array of all the field values. The `$(NF)` variable is defined to be the number of fields.

Next, the cases are evaluated in order. For each case, if the regular expression `pattern_i` matches the record `$0`, then `body_i` is evaluated. If the body ends in an `export`, the state is passed to the next clause. Otherwise the value is discarded. If the regular expression contains `\(r\)` expression, those expression override the fields `$1, $2, ...`.

For example, here is an `awk` function to print the text between two delimiters `\begin{<name>}` and `\end{<name>}`, where the `<name>` must belong to a set passed as an argument to the `filter` function.

        filter(names) =
           print = false

           awk(Awk.in)
           case $"^\\end\{\([:alpha:]+\)\}"
              if $(mem $1, $(names))
                 print = false
                 export
              export
           default
              if $(print)
                 println($0)
           case $"^\\begin\{\([:alpha:]+\)\}"
              print = $(mem $1, $(names))
              export

Note, if you want to redirect the output to a file, the easiest way is to redefine the `stdout` variable. The `stdout` variable is scoped the same way as other variables, so this definition does not affect the meaning of `stdout` outside the `filter` function.

        filter(names) =
            stdout = $(fopen file.out, w)
            awk(Awk.in)
               ...
            close(stdout)

Options.

b
  “Break” when evaluating cases. Only the first case that matches will be selected.

The `break` function can be used to abort the loop, exiting the `awk` function immediately.

### 9.11.6 fsubst

       fsubst(files)
       case pattern1 [options]
          body1
       case pattern2 [options]
          body2
       ...
       default
          bodyd

The `fsubst` function provides a `sed`(1)-like substitution function. Similar to `awk`, if `fsubst` is called with no arguments, the input is taken from `stdin`. If arguments are provided, each specifies an `InChannel`, or the name of a file for input.

The `RS` variable defines a regular expression that determines a record separator, The default value of `RS` is the regular expression `\r|\n|\r\n`.

The `fsubst` function reads the file one record at a time.

For each record, the cases are evaluated in order. Each case defines a substitution from a substring matching the `pattern` to replacement text defined by the body.

Currently, there is only one option: `g`. If specified, each clause specifies a global replacement, and all instances of the pattern define a substitution. Otherwise, the substitution is applied only once.

Output can be redirected by redefining the `stdout` variable.

For example, the following program replaces all occurrences of an expression `word.` with its capitalized form.

        section
           stdout = $(fopen Subst.out, w)
           fsubst(Subst.in)
           case $"\<\([[:alnum:]]+\)\." g
              value $(capitalize $1).
           close(stdout)

### 9.11.7 lex

       lex(files)
       case pattern1
          body1
       case pattern2
          body2
       ...
       default
          bodyd

The `lex` function provides a simple lexical-style scanner function. The input is a sequence of files or channels. The cases specify regular expressions. Each time the input is read, the regular expression that matches the longest prefix of the input is selected, and the body is evaluated.

If two clauses both match the same input, the last one is selected for execution. The `default` case matches the regular expression `.`; you probably want to place it first in the pattern list.

If the body end with an `export` directive, the state is passed to the next clause.

For example, the following program collects all occurrences of alphanumeric words in an input file.

        collect-words($(files)) =
           words[] =
           lex($(files))
           default
              # empty
           case $"[[:alnum:]]+" g
              words[] += $0
              export

The `default` case, if one exists, matches single characters. Since

It is an error if the input does not match any of the regular expressions.

The `break` function can be used to abort the loop.

### 9.11.8 lex-search

       lex-search(files)
       case pattern1
          body1
       case pattern2
          body2
       ...
       default
          bodyd

The `lex-search` function is like the `lex` function, but input that does not match any of the regular expressions is skipped. If the clauses include a `default` case, then the `default` matches any skipped text.

For example, the following program collects all occurrences of alphanumeric words in an input file, skipping any other text.

        collect-words($(files)) =
           words[] =
           lex-search($(files))
           default
              eprintln(Skipped $0)
           case $"[[:alnum:]]+" g
              words[] += $0
              export

The `default` case, if one exists, matches single characters. Since

It is an error if the input does not match any of the regular expressions.

The `break` function can be used to abort the loop.

### 9.11.9 Lexer

The `Lexer` object defines a facility for lexical analysis, similar to the `lex`(1) and `flex`(1) programs.

In `omake`, lexical analyzers can be constructed dynamically by extending the `Lexer` class. A lexer definition consists of a set of directives specified with method calls, and set of clauses specified as rules.

For example, consider the following lexer definition, which is intended for lexical analysis of simple arithmetic expressions for a desktop calculator.

       lexer1. =
          extends $(Lexer)

          other: .
             eprintln(Illegal character: $* )
             lex()

          white: $"[[:space:]]+"
             lex()

          op: $"[-+*/()]"
             switch $*
             case +
                Token.unit($(loc), plus)
             case -
                Token.unit($(loc), minus)
             case *
                Token.unit($(loc), mul)
             case /
                Token.unit($(loc), div)
             case $"("
                Token.unit($(loc), lparen)
             case $")"
                Token.unit($(loc), rparen)

          number: $"[[:digit:]]+"
             Token.pair($(loc), exp, $(int $* ))

          eof: $"\'"
             Token.unit($(loc), eof)

This program defines an object `lexer1` the extends the `Lexer` object, which defines lexing environment.

The remainder of the definition consists of a set of clauses, each with a method name before the colon; a regular expression after the colon; and in this case, a body. The body is optional, if it is not specified, the method with the given name should already exist in the lexer definition.

NB The clause that matches the longest prefix of the input is selected. If two clauses match the same input prefix, then the last one is selected. This is unlike most standard lexers, but makes more sense for extensible grammars.

The first clause matches any input that is not matched by the other clauses. In this case, an error message is printed for any unknown character, and the input is skipped. Note that this clause is selected only if no other clause matches.

The second clause is responsible for ignoring white space. If whitespace is found, it is ignored, and the lexer is called recursively.

The third clause is responsible for the arithmetic operators. It makes use of the `Token` object, which defines three fields: a `loc` field that represents the source location; a `name`; and a `value`.

The lexer defines the `loc` variable to be the location of the current lexeme in each of the method bodies, so we can use that value to create the tokens.

The `Token.unit($(loc), name)` method constructs a new `Token` object with the given name, and a default value.

The `number` clause matches nonnegative integer constants. The `Token.pair($(loc), name, value)` constructs a token with the given name and value.

Lexer object operate on `InChannel` objects. The method `lexer1.lex-channel(channel)` reads the next token from the channel argument.

### 9.11.10 Lexer matching

During lexical analysis, clauses are selected by longest match. That is, the clause that matches the longest sequence of input characters is chosen for evaluation. If no clause matches, the lexer raises a `RuntimeException`. If more than one clause matches the same amount of input, the first one is chosen for evaluation.

### 9.11.11 Extending lexer definitions

Suppose we wish to augment the lexer example so that it ignores comments. We will define comments as any text that begins with the string `(*`, ends with `*)`, and comments may be nested.

One convenient way to do this is to define a separate lexer just to skip comments.

       lex-comment. =
          extends $(Lexer)

          level = 0

          other: .
             lex()

          term: $"[*][)]"
             if $(not $(eq $(level), 0))
                level = $(sub $(level), 1)
                lex()

          next: $"[(][*]"
             level = $(add $(level), 1)
             lex()

          eof: $"\'"
             eprintln(Unterminated comment)

This lexer contains a field `level` that keeps track of the nesting level. On encountering a `(*` string, it increments the level, and for `*)`, it decrements the level if nonzero, and continues.

Next, we need to modify our previous lexer to skip comments. We can do this by extending the lexer object `lexer1` that we just created.

       lexer1. +=
          comment: $"[(][*]"
             lex-comment.lex-channel($(channel))
             lex()

The body for the comment clause calls the `lex-comment` lexer when a comment is encountered, and continues lexing when that lexer returns.

### 9.11.12 Threading the lexer object

Clause bodies may also end with an `export` directive. In this case the lexer object itself is used as the returned token. If used with the `Parser` object below, the lexer should define the `loc`, `name` and `value` fields in each `export` clause. Each time the `Parser` calls the lexer, it calls it with the lexer returned from the previous lex invocation.

### 9.11.13 Parser

The `Parser` object provides a facility for syntactic analysis based on context-free grammars.

`Parser` objects are specified as a sequence of directives, specified with method calls; and productions, specified as rules.

For example, let's finish building the desktop calculator started in the `Lexer` example.

       parser1. =
          extends $(Parser)

          #
          # Use the main lexer
          #
          lexer = $(lexer1)

          #
          # Precedences, in ascending order
          #
          left(plus minus)
          left(mul div)
          right(uminus)

          #
          # A program
          #
          start(prog)

          prog: exp eof
             return $1

          #
          # Simple arithmetic expressions
          #
          exp: minus exp :prec: uminus
             neg($2)

          exp: exp plus exp
             add($1, $3)

          exp: exp minus exp
             sub($1, $3)

          exp: exp mul exp
             mul($1, $3)

          exp: exp div exp
             div($1, $3)

          exp: lparen exp rparen
             return $2

Parsers are defined as extensions of the `Parser` class. A `Parser` object must have a `lexer` field. The `lexer` is not required to be a `Lexer` object, but it must provide a `lexer.lex()` method that returns a token object with `name` and `value` fields. For this example, we use the `lexer1` object that we defined previously.

The next step is to define precedences for the terminal symbols. The precedences are defined with the `left`, `right`, and `nonassoc` methods in order of increasing precedence.

The grammar must have at least one start symbol, declared with the `start` method.

Next, the productions in the grammar are listed as rules. The name of the production is listed before the colon, and a sequence of variables is listed to the right of the colon. The body is a semantic action to be evaluated when the production is recognized as part of the input.

In this example, these are the productions for the arithmetic expressions recognized by the desktop calculator. The semantic action performs the calculation. The variables `$1, $2, ...` correspond to the values associated with each of the variables on the right-hand-side of the production.

### 9.11.14 Calling the parser

The parser is called with the `$(parser1.parse-channel start, channel)` or `$(parser1.parse-file start, file)` functions. The `start` argument is the start symbol, and the `channel` or `file` is the input to the parser.

### 9.11.15 Parsing control

The parser generator generates a pushdown automation based on LALR(1) tables. As usual, if the grammar is ambiguous, this may generate shift/reduce or reduce/reduce conflicts. These conflicts are printed to standard output when the automaton is generated.

By default, the automaton is not constructed until the parser is first used.

The `build(debug)` method forces the construction of the automaton. While not required, it is wise to finish each complete parser with a call to the `build(debug)` method. If the `debug` variable is set, this also prints with parser table together with any conflicts.

The `loc` variable is defined within action bodies, and represents the input range for all tokens on the right-hand-side of the production.

### 9.11.16 Extending parsers

Parsers may also be extended by inheritance. For example, let's extend the grammar so that it also recognizes the `<<` and `>>` shift operations.

First, we extend the lexer so that it recognizes these tokens. This time, we choose to leave `lexer1` intact, instead of using the += operator.

       lexer2. =
          extends $(lexer1)

          lsl: $"<<"
             Token.unit($(loc), lsl)

          asr: $">>"
             Token.unit($(loc), asr)

Next, we extend the parser to handle these new operators. We intend that the bitwise operators have lower precedence than the other arithmetic operators. The two-argument form of the `left` method accomplishes this.

       parser2. =
          extends $(parser1)

          left(plus, lsl lsr asr)

          lexer = $(lexer2)

          exp: exp lsl exp
             lsl($1, $3)

          exp: exp asr exp
             asr($1, $3)

In this case, we use the new lexer `lexer2`, and we add productions for the new shift operations.

### 9.11.17 Passwd

The `Passwd` object represents an entry in the system's user database. It contains the following fields.

  `pw_name`: the login name.
  `pw_passwd`: the encrypted password.
  `pw_uid`: user id of the user.
  `pw_gid`: group id of the user.
  `pw_gecos`: the user name or comment field.
  `pw_dir`: the user's home directory.
  `pw_shell`: the user's default shell.

Not all the fields will have meaning on all operating systems.

### 9.11.18 getpwnam, getpwuid

        $(getpwnam name...) : Passwd
           name : String
        $(getpwuid uid...) : Passwd
           uid : Int
        raises RuntimeException

The `getpwnam` function looks up an entry by the user's login and the `getpwuid` function looks up an entry by user's numerical id (uid). If no entry is found, an exception will be raised.

### 9.11.19 getpwents

        $(getpwents) : Array

The `getpwents` function returns an array of `Passwd` objects, one for every user fund in the system user database. Note that depending on the operating system and on the setup of the user database, the returned array may be incomplete or even empty.

### 9.11.20 Group

The `Group` object represents an entry in the system's user group database. It contains the following fields.

  `gr_name`: the group name.
  `gr_group`: the encrypted password.
  `gr_gid`: group id of the group.
  `gr_mem`: the group member's user names.

Not all the fields will have meaning on all operating systems.

### 9.11.21 getgrnam, getgrgid

        $(getgrnam name...) : Group
           name : String
        $(getgrgid gid...) : Group
           gid : Int
        raises RuntimeException

The `getgrnam` function looks up a group entry by the group's name and the `getgrgid` function looks up an entry by groups's numerical id (gid). If no entry is found, an exception will be raised.

### 9.11.22 tgetstr

       $(tgetstr id) : String
          id : String

The `tgetstr` function looks up the terminal capability with the indicated `id`. This assumes the terminfo to lookup is given in the `TERM` environment variable. This function returns an empty value if the given terminal capability is not defined.

Note: if you intend to use the value returned by `tgetstr` inside the shell `prompt`, you need to wrap it using the `prompt-invisible` function.

### 9.11.23 xterm-escape-begin, xterm-escape-end

       $(xterm-escape-begin) : String
       $(xterm-escape-end) : String

The `xterm-escape-begin` and `xterm-escape-end` functions return the escape sequences that can be used to set the XTerm window title. Will return empty values if this capability is not available.

Note: if you intend to use these strings inside the shell `prompt`, you need to use `$(prompt_invisible_begin)$(xterm-escape-begin)` and `$(xterm-escape-end)$(prompt_invisible_end)`.

### 9.11.24 xterm-escape

       $(xterm-escape s) : Sequence

When the `TERM` environment variable indicates that the XTerm title setting capability is available, `$(xterm-escape s)` is equivalent to `$(xterm-escape-begin)s$(xterm-escape-end)`. Otherwise, it returns an empty value.

Note: if you intend to use the value returned by `xterm-escape` inside the shell `prompt`, you need to wrap it using the `prompt-invisible` function.

### 9.11.25 prompt-invisible-begin, prompt-invisible-end

       $(prompt-invisible-begin) : String
       $(prompt-invisible-end) : String

The `prompt-invisible-begin` and `prompt-invisible-end` functions return the escape sequences that must used to mark the “invisible” sections of the shell `prompt` (such as various escape sequences).

### 9.11.26 prompt-invisible

       $(prompt-invisible s) : Sequence

The `prompt-invisible` will wrap its argument with `$(prompt-invisible-begin)` and `$(prompt-invisible-end)`. All the `invisible” sections of the shell `prompt` (such as various escape sequences) must be wrapped this way.

### 9.11.27 gettimeofday

       $(gettimeofday) : Float

The `gettimeofday` function returns the time of day in seconds since January 1, 1970.

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