Created: 2014-05-19 07:15
Updated: 2015-10-07 17:27



A Lua function that pipes a Lua string through an external command and returns the result as another Lua string. The function only catches data from stdout.

Also provided is a helper function that mimics building a pipeline on the command line so that you can write $(mount | column -t | tac) in handy Lua.

Examples are provided below.


  • lua-posix


local fpipe = require 'filterpipe'

local result = fpipe.pipe( input, command, ... )
-- where $input is the input string, $command is the command to execute
-- and the ellipsis ... represents arguments to be passed through to
-- $command. The function returns a Lua string $result.

local result2 = fpipe._( t, input )
-- where $t is an array of tables that are structured like { command,
-- ...} where $command is the command to execute and all other array
-- elements represent arguments passed through to $command. All commands
-- in the array will be executed sequentially and the output be piped
-- through the whole pipeline. An initial $input (a Lua string) can be
-- provided, too. The function returns a Lua string $result2.

Example: Aligned output using the column command

local fpipe = require 'filterpipe'

  fpipe( "abc?def?ghi\njklmnop?qr\nstu\tvwx\n", -- the trailing \n is required by column
    "column", -- the command
    "-t", "-s?")) -- parameters


abc      def  ghi
jklmnop  qr
stu	vwx

Example: Columnate and reverse output of the mount command

local fpipe = require 'filterpipe'

-- equals $(mount | columnt -t | tac) on the command line
  fpipe._{ {"mount"}, {"column", "-t"}, {"tac"} }

Example output on my local machine:

binfmt_misc                        on  /proc/sys/fs/binfmt_misc  type  binfmt_misc  (rw,nosuid,nodev,noexec,relatime)
cgroups                            on  /sys/fs/cgroup            type  cgroup       (rw,relatime,cpu,blkio)
/dev/mapper/vgroot-home--overflow  on  /mnt/home-overflow        type  xfs          (rw,relatime,attr2,inode64,noquota)
/dev/mapper/vgroot-overflow        on  /mnt/overflow             type  ext4         (rw,relatime,data=ordered)
/dev/mapper/vgroot-home            on  /home                     type  ext4         (rw,relatime,data=ordered)
/dev/sda1                          on  /boot                     type  ext2         (rw,relatime,errors=continue)
tmpfs                              on  /tmp                      type  tmpfs        (rw,nosuid,relatime,size=4194304k,mode=777)
fusectl                            on  /sys/fs/fuse/connections  type  fusectl      (rw,relatime)
tmpfs                              on  /run/shm                  type  tmpfs        (rw,nosuid,nodev,noexec,relatime,size=1553760k)
/dev/sda1                          on  /media/usbhd-sda1         type  ext2         (rw,relatime,errors=continue)
pstore                             on  /sys/fs/pstore            type  pstore       (rw,relatime)
tmpfs                              on  /run/lock                 type  tmpfs        (rw,nosuid,nodev,noexec,relatime,size=5120k)
/dev/mapper/vgroot-root            on  /                         type  ext4         (rw,relatime,errors=remount-ro,data=ordered)
tmpfs                              on  /run                      type  tmpfs        (rw,nosuid,noexec,relatime,size=776884k,mode=755)
devpts                             on  /dev/pts                  type  devpts       (rw,nosuid,noexec,relatime,gid=5,mode=620)
udev                               on  /dev                      type  devtmpfs     (rw,relatime,size=10240k,nr_inodes=968868,mode=755)
proc                               on  /proc                     type  proc         (rw,nosuid,nodev,noexec,relatime)
sysfs                              on  /sys                      type  sysfs        (rw,nosuid,nodev,noexec,relatime)
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