LuaPosix

From Alpine Linux

This is a list of the Lua Posix functions. Included is helpful snippets of code. Install lua posix. To get this list do: 

require "posix"
for a in pairs(posix) do 
  print(a)
end

access

check real user's permissions for a file

Synopsis

posix.access(pathname, mode)

Description

access() checks whether the calling process can access the file pathname. If pathname is a symbolic link, it is dereferenced.

The mode specifies the accessibility check(s) to be performed, and is either the string "f", or one or more of "r", "w", and "x". "f" tests for the existence of the file. "r", "w", and "x" test whether the file exists and grants read, write, and execute permissions, respectively.

Return Value

On success (all requested permissions granted), zero is returned. On error (at least one char in mode asked for a permission that is denied, or some other error occurred), nil, errorstr and errno is returned.

Examples

status, errstr, errno = posix.access("/etc/passwd", "rw")

if not posix.access("/foo", "f") then
  print("/foo does not exist")
end

References

https://man7.org/linux/man-pages/man2/access.2.html

chdir

change working directory

Synopsis

posix.chdir(path)

Return Value

On success, zero is returned. On error, nil, an error string and errno is returned.

Examples

status, errstr, errno = posix.chdir("/tmp")

if posix.chdir("/tmp") then
  print("Changed current working dir to:", posix.getpwd())
fi

chmod

change permissions of a file

Synopsis

posix.chmod(path, mode)

Description

The mode of the file given by path is changed.

Modes are specified in one of the following formats

  • "rwxrwxrwx" (i.e "rw-rw-w--")
  • "ugoa+-=rwx" (i.e "u+w")
  • "+-=rwx" (i.e "+w")

Return Value

On success, zero is returned. On error, nil, errstr and errno is returned.

Examples

posix.chmod("/tmp", "a+rwx")

status, errstr = posix.chmod(file, "-w")
if not status then
  print(errstr)
fi

chown

INPUT

  • Path-location of file or directory
  • UID - User id number
  • GID - Group id number

OUPUT

  • String - 0 is success and nil for failure
bar = require "posix"
print(bar.chown("/etc/passwd",100,200)
--above will give back nil. Since we printed it will also give back the system errors.

clock_getres

TODO

clock_gettime

TODO

crypt

password and data encryption

Synopsis

posix.crypt(string, salt)

Return Value

On success, zero is returned. On error, nil, an error string and errno is returned.


ctermid

INPUT

  • NONE- DISPLAYS the terminal id

OUTPUT

  • String with the terminal id
bar = require "posix"
print(bar.ctermid())

dir

read a directory

Synopsis

posix.dir(path)

Description

Reads directory path, and returns a table with all the files. If path is omitted, current working dir is read.

Return Value

posix.dir() returns a table with all filenames on succes. On error, nil, an error string and errno is returned.

Examples

files, errstr, errno = posix.dir("/var/log")
if files then
  for a,b in ipairs(files) do
    print(b)
  end
else
  print(errstr)
end

dup

duplicate a file descriptor

Synopsis

posix.dup(oldfd[, newfd])

Description

posix.dup() creates a copy of the file descriptor oldfd.

newfd will be the copy of oldfd, closing newfd first if necessary.

If newfd is omitted, the lowest-numbered unused descriptor will be used for the new descriptor.

Return Value

posix.dup() returns the new descriptor, or nil, an error string and errno if an error occured.

errno

Display the error information

INPUT

  • NONE

OUPUT

  • Success, or Error message
bar = require "posix"
a,b = bar.dir("/var/foo"), bar.errno()
print(a,b)
-- a will be nil or 0, b will be No such file or directory or Success

exec

execute a file

Synopsis

posix.exec(path,[args])

Description

exec() replaces the current process image with a new process image.

Return Value

On success exec() will not return. On error nil, errstr and errno is returned.

execp

execute a file using PATH environment variable

Synopsis

posix.execp(path,[args])

Description

execp() replaces the current process image with a new process image. If path does not contain a slash (/) character the file wil be searched for in PATH environment variable.

Return Value

On success execp() will not return. On error nil, errstr and errno is returned.


mkfifo

INPUT

  • PATH- where to make the fifo

OUPUT

  • 0 for success, nil for failure
bar = require "posix"
print(bar.mkfifo("/tmp/bobo"))
--Returns 0 for success, nil for failure

files

Returns an interator function that loops over each file in the given directory

INPUT

  • PATH- Directory

OUPUT 

require "posix"

for name in posix.files("/etc") do
    print (name)
end

fork

INPUT

  • None

OUTPUT returns: -1 on error, 0 to the child process, and the pid of the child to the parent. 

require("posix")

print ("parent: my pid is: " .. posix.getpid("pid")) 

local pid = posix.fork () 

if ( pid == -1 ) then
        print ("parent: The fork failed.")
elseif ( pid == 0 ) then
        print ("child: Hello World! I am pid: " .. posix.getpid("pid") )
        print ("child: I'll sleep for 1 second ... ")
        posix.sleep(1)
        print ("child: Good bye");
else
        print ("parent: While the child sleeps, I'm still running.")
        print ("parent: waiting for child (pid:" .. pid .. ") to die...")
        posix.wait(pid)
        print ("parent: child died, but I'm still alive.")
        print ("parent: Good bye")
end

parent: my pid is: 11050
child: Hello World! I am pid: 11051
child: I'll sleep for 1 second ... 
parent: While the child sleeps, I'm still running.
parent: waiting for child (pid:11051) to die...
child: Good bye
parent: child died, but I'm still alive.
parent: Good bye

gmtime

TODO

getcwd

Get current working directory INPUT

  • NONE

OUTPUT

  • String- contents of which is the current working directory
require "posix"
print(posix.getcwd())

getenv

INPUT

  • NONE

OUPUT

  • Table - Current Environment settings
bar = require "posix"
bobo = bar.getenv()
for a,b in pairs(bobo) do print(b) end
-- Varible - Value

getgroup

INPUT

  • GID, or groupname

OUPUT

  • TABLE -contents of which hold the group name,gid, and users
bar = require "posix"
bobo = bar.getgroup(1000)
for a,b in pairs(bobo) do print(a,b) end
--if you use pairs then bobo will print also the name and gid or the group
--if you use ipairs then just the group members
1 user1
2 user2
name wheel
gid 1

getlogin

get user name

Synopsis

posix.getlogin()

Description

getlogin() returns a string containing the name of the user logged in on the controlling terminal of the process, or nil if this information cannot be determined.

Examples

print(posix.getlogin())

getrlimit

TODO

getpasswd

get password file entry

Synopsis

posix.getpasswd(user, field)

Description

getpasswd() queries the local /etc/passwd database. user can be either an uid or a username. field is a string of one of "uid", "name", "gid", "password", "gecos", "dir" or "shell".

Return Value

Returns the value of field for user. If field is omitted, a table with all fields is returned.

Examples

for a,b in pairs(posix.getpasswd("root")) do
  print(a,b)
end

Output: 

uid     0
name    root
gid     0
passwd  x
gecos   root
dir     /root
shell   /bin/bash

print(posix.getpasswd("root", "shell"))

Output: 

/bin/sh

getprocessid

INPUT

  • Selector - either [egid,euid,gid,uid,pgrp,pid,ppid,NULL]

OUPUT

  • Number that matches the current process and the selector
bar = require "posix"
print(bar.getprocessid("gid"))
18456 
--it just printed the current process id for the script or interactive lua.


Is there a version difference here? AL 1.7.7 calls this "getpid" Nangel

gettimeofday

TODO

glob

find pathnames matching a pattern

Synopsis

posix.glob(pattern)

Description

The glob() function searches for all the pathnames matching pattern according to the rules used by the shell.

Return Value

On successful comlpetion, glob() returns a table with the filenames. On error glob() returns nil, errstr and errno.

Examples

for i,j in pairs(posix.glob("/proc/[0-9]*/exe")) do
  local f = posix.readlink(j)
  if f then
    print(f)
  end
end

kill

INPUT

  • PID- process identifier
  • Signal- to send to the process

OUPUT 

bar = require "posix"
--kill your current process
bobo = bar.getprocessid("pid")
bar.kill(bobo,9)
---Signals looks to be the number signals accepted in Unix

link

make a new name for a file

Synopsis

posix.dup(oldpath, newpath[, symbolic])

Description

Creates a new name to an existing file. If symbolic is true the new name will be a symbolic link (soft link), otherwise it will be a hard link.

Return Value

On success, zero is returned. On error link() returns nil, errstr and errno.

Examples

require "posix"
source="/etc/passwd"
dest="testfile"
status, errstr = posix.link(source, dest, true)
if status == nil then
  io.stderr:write(dest..": "..errstr.."\n")
end


localtime

TODO

mkdir

create a directory

Synopsis

posix.dup(pathname)

Descritption

mkdir() attempts to create a directory named pathname.

Return Value

glob() returns 0 on success, or nil, errstr and errno on error.

Example

require "posix"
newdir = "/home/user/bobo"
status, errstr = posix.mkdir(newdir)
if status == nil then
        io.stderr:write(newdir..": "..errstr.."\n")
end


pathconf

get configuration values for files

Synopsis

posix.pathconf(path, name)

Description

posix.pathconf() gets a value for configuration option name for the filename path. Setting name equal to one of the following strings returns the following configuration options:

  • link_max
    • returns the maximum number of links to the file. If path refer to a directory, then the value applies to the whole directory.
  • max_canon
    • returns the maximum length of a formatted input line, where path must refer to a terminal.
  • max_input
    • returns the maximum length of an input line, where path must refer to a terminal.
  • name_max
    • returns the maximum length of a filename in the directory path the process is allowed to create.
  • path_max
    • returns the maximum length of a relative pathname when path is the current working directory.
  • pipe_buf
    • returns the size of the pipe buffer, where path must refer to a FIFO.
  • chown_restricted
    • returns non-zero if the chown(2) call may not be used on this file. If path refer to a directory, then this applies to all files in that directory.
  • no_trunc
    • returns non-zero if accessing filenames longer than name_max generates an error.
  • vdisable
    • returns non-zero if special character processing can be disabled, where path must refer to a terminal.

Return Value

The limit is returned, if one exists. If name is omitted, a table of all limits is returned.

Examples

for i,j in pairs(posix.pathconf("/dev/tty" )) do
  print(i, j)
end

Will ouput: 

pipe_buf        4096
link_max        127
path_max        4096
max_canon       255
chown_restricted        1
no_trunc        1
max_input       255
name_max        255
vdisable        0

References

https://man7.org/linux/man-pages/man3/pathconf.3.html

pipe

TODO

Example

require "posix"
rd, wr = posix.pipe()
wr:write("hello, world\n")
wr:close()
print(rd:read("*all"))
rd:close()

putenv

INPUT

  • STRING-

OUPUT

  • 0 if success, nil if not
require "posix"
posix.putenv("DISPLAY=localhost:0")

readlink

INPUT

  • PATH-path to link

OUPUT

  • 0 if success, nil if failure
require "posix"
posix.readlink("/etc/rc.d/postfix")
--0 if sucess, nil if failed

rmdir

INPUT

  • PATH- path to directory

OUPUT

  • 0 for sucess
  • nil for failure
require "posix"
posix.rmdir("/home/testdir")
-- 0 for success, nil for failure

setgid

INPUT

  • Group
    • Name or GID

OUPUT

  • 0 for sucess
  • nil for failure
require "posix"
posix.setgid("1000")

setlogmask

TODO

setrlimit

TODO

setuid

INPUT

  • User
    • Name or UID

OUPUT

  • 0 for sucess, nil for failure
require "posix"
posix.setuid("1000")
-- 0 for sucess, nil for failure

sleep

INPUT

  • SECONDS

OUPUT

  • 0 for sucess, nil for failure
require "posix"
posix.sleep(5)
-- will sleep for 5 seconds, usually will not fail

stat

INPUT

  • PATH - location of file or direcory
  • Selector -
    • dev
    • type
    • ctime
    • nlink
    • atime
    • uid
    • mtime
    • gid
    • mode
    • ino
    • size

OUPUT

  • If no mode will output as a table with each of the above set
  • If mode is set then will give a string with value
require "posix"
bar = posix.stat("/etc/")
for a,b in pairs(bar) do print(a,b) end
dev     769
type    directory
ctime   1194624026
nlink   113
atime   1194866712
uid     0
mtime   1194624026
gid     0
mode    rwxr-xr-x
ino     4
size    6208

sysconf

INPUT

  • Accept a selector if given anything
    • tzname_max
    • clk_tck
    • stream_max
    • ngroups_max
    • child_max
    • open_max
    • saved_ids
    • job_control
    • version
    • arg_max

OUPUT

  • TABLE - if no selector
  • STRING - if 1 selector
require "posix"
bar = posix.stat()
for a,b in pairs(bar) do print(a,b) end
tzname_max      6
clk_tck 100
stream_max      16
ngroups_max     65536
child_max       999
open_max        1024
saved_ids       1
job_control     1
version 200112
arg_max 131072

strftime

TODO

time

TODO

times

INPUT

    • utime
    • cstime
    • elapsed
    • cutime
    • stime

OUPUT

  • TABLE - if non specified output all values in a table
  • STING - if one of the above is specified string output
require "posix"
bar = posix.times()
for a,b in pairs(bar) do print(a,b) end
--Maybe takes function calls to see how long they run

ttyname

INPUT

  • NONE

OUPUT

  • STRING - what tty am I on
require "posix"
print(posix.ttyname())

umask

INPUT

  • NONE
    • or mode, what to change the umask to

OUPUT

  • STRING - what is the current umask set to
    • or mode, what to change is to
require "posix"
print(posix.umask)
-- rwxr-xr-x
--or change it
posix.umask("a=rwx")
print(posix.umask())
-- rwxrwxrwx

uname

get name and information about current kernel

Synopsis

posix.access([format])

Description

uname() returns the string format with directives prefixed by '%' replaced with specified systrem information. If format is not specified or is nil, then the string "%s %n %r %v %m" will be used.

The format string directives are: 

%s - kernel name
%n - network node hostname
%r - kernel release
%v - kernel version
%m - machine hardware name

Return Value

A string with the formatted system information.

Examples

print("Kernel version is: "..posix.uname("%v"))

References

https://man7.org/linux/man-pages/man2/uname.2.html

utime

INPUT

  • Path-location of file or directory
    • atime - access time
    • mtime - modification time

OUPUT

  • 0 for sucess
  • nil for failure
require "posix"
posix.utime("/var/log/test",atime,mtime)

wait

INPUT

  • PID - process id

OUPUT

  • 0 for success
  • nil for failure
require "posix"
posix.wait(10)

If you are using this under linux also get

setenv

INPUT

  • Name- Name of Varible
  • Value- What the Name varible should be set to
    • overwrite- is this overwriting one already set

OUPUT

  • 0 for sucess, nil for failure
require "posix"
posix.setenv("BAR","YES")

unsetenv

INPUT

  • NAME - name of the varible to unset

OUPUT

  • 0 for sucess, nil for failure
require "posix"
posix.unsetenv("BAR")
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