HowTo One Liners

Overview

This page provides a quick reference to common One Liner administrative command line operations.

One Liner Resources

• A Regular Expression Reference

• Regular Expression Online Tool

• Sed and Regular Expressions

• Linux - Regular Expressions Tutorial with Sed

• A Javascript Regular Expressions Tutorial

• Handy One Liners for Sed: Sed - LinuxHowtos, Sed - SourceForge, Sed - Gist

• GNU Sed Homepage

• A Sed Tutorial

• Sed Part1, Sed Part2 and Sed Part3

• Advanced Parsing for Pentesters

• GNU Gawk Homepage

• The GNU Awk User’s Guide

• An Awk Tutorial

• Awk Array Examples

• Text Streams and Filters

• A Grep Tutorial

• A Find Example

• A Tar Tutorial

Get Syntax Color In Less

The NST includes the source-highlight package which can "smartly" apply color to a wide variety of file formats. You can set some less environment variables to make use of the source-hightlight package to color code files in your terminal with the following settings:

export LESSOPEN="| source-highlight --out-format=esc -o STDOUT -i %s 2>/dev/null"; export LESS=" -R "

Then try something like:

less /usr/share/nstwui/apps/arp-scan/arp-scan.js
less /usr/bin/lsusb.py

Unfortunately, source-highlight only works by filename extensions (it won't try to guess the input format based on the contents of the file).

Find The Largest Files Within A File System

This example finds the 10 largest files, descending sorted, using the "/var" top level directory:

[root@vortex wui]# find /var -printf '%s %p\n' | sort -nr | head -10;
29956694633 /var/named/chroot/var/named/data/default_debug.log
182947840 /var/lib/rpm/Packages
134217728 /var/log/journal/597d443ff603490286135ca186ed9c7d/system@f9cb0e593f6c413d8fdfaa88bd1c9f42-00000000000b1d98-0005092323239c17.journal
125829120 /var/log/journal/597d443ff603490286135ca186ed9c7d/system@f9cb0e593f6c413d8fdfaa88bd1c9f42-000000000008eadb-000506c496be90cb.journal
125829120 /var/log/journal/597d443ff603490286135ca186ed9c7d/system@f9cb0e593f6c413d8fdfaa88bd1c9f42-00000000000251f3-0004f57678d900a6.journal
125829120 /var/log/journal/597d443ff603490286135ca186ed9c7d/system@f9cb0e593f6c413d8fdfaa88bd1c9f42-0000000000000001-0004f10922bc1e86.journal
95967232 /var/cache/yum/x86_64/20/fedora/gen/primary_db.sqlite
83886080 /var/log/journal/597d443ff603490286135ca186ed9c7d/system@f9cb0e593f6c413d8fdfaa88bd1c9f42-0000000000077d06-00050460486ab015.journal
75497472 /var/log/journal/597d443ff603490286135ca186ed9c7d/system@f9cb0e593f6c413d8fdfaa88bd1c9f42-000000000004d2bc-0004fbc9efdbc627.journal
64720632 /var/lib/clamav/main.cvd

Use SSH To Login On Remote System Using A Different New Shell

The command below demonstrates how to login on to a remote system using a different shell (i.e., /bin/ash):

imac2012:~ rwhalb$ ssh -t root@10.222.222.8 /bin/ash
root@10.222.222.8's password: 
Warning: untrusted X11 forwarding setup failed: xauth key data not generated

BusyBox v1.30.1 () built-in shell (ash)

~ # exit
Connection to 10.222.222.8 closed.
imac2012:~ rwhalb$

Used sed to Remove All Carriage Lines (\r, ^M) from a File

sed -i -e 's/\r//g' <file>

Use sed to Remove the Next Line from a Previous Line Match

Lets say you need to remove a specific line from a file that is replicated throughout the file:

Example: The second #endif line from a file: "types.h" will be removed after matching line: typedef uint64_t __u64;

.
.
.
#ifndef LIBZWAVE_EXCLUDE_TYPES
  typedef ZWAVE_NULL 0;
#endif

#ifndef LIBWIFIUSERSPACE_EXCLUDE_TYPES
  typedef uint8_t __u8;
  typedef uint16_t __u16;
  typedef uint32_t __u32;
  typedef uint64_t __u64;
#endif
.
.
.

Use this sed one liner to remove the second #endif after line: typedef uint64_t __u64;:

sed -i -e '/typedef uint64_t __u64;/{n;d;}' "./types.h";

Results:

.
.
.
#ifndef LIBZWAVE_EXCLUDE_TYPES
  typedef ZWAVE_NULL 0;
#endif

#ifndef LIBWIFIUSERSPACE_EXCLUDE_TYPES
  typedef uint8_t __u8;
  typedef uint16_t __u16;
  typedef uint32_t __u32;
  typedef uint64_t __u64;
.
.
.

Use sed to Remove Multiple Next Lines from a Previous Line Match

Lets say you need to remove multiple lines from a file after a previous line match:

Example: Remove lines containing: 4, 6 and 8 from a file: "letters.txt" after matching line: abc1

.
.
.
abc1
4
6
8
9
.
.
.

Use this sed one liner:

sed -i -e '/abc1/{n;N;N;d;}' "./letters.txt";

Results:

.
.
.
abc1
9
.
.
.

Remove Incorrect Host Key from ~/.ssh/known_hosts (Delete 1 Line from File)

The sed command can be very useful when you want to remove a specific line from a file. For example, the following command can be used to remove line 12 out of the file: ~/.ssh/known_hosts.

 sed -i -e 12d ~/.ssh/known_hosts

Alternatively, you can add a rmsshhost function to your ~/.bash_profile:

 rmsshhost() {
   sed -i -e ${1:-999999999}d ${2:-~/.ssh/known_hosts};
 }

This is particularly useful in situations where ssh host keys are expected to change. For example, depending on which micro SD card is loaded on a Beagle Bone Black, it's host key might change. The following demonstrates the output from ssh when it detects this change in the host key (note how it reports the problem line as 54). The sed command is then used to quickly remove the old key.

taco:~ pkb$ ssh salsa-e
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
fb:a7:a9:09:1a:f3:d2:4a:aa:89:9d:34:47:1c:d5:3c.
Please contact your system administrator.
Add correct host key in /Users/pkb/.ssh/known_hosts to get rid of this message.
Offending RSA key in /Users/pkb/.ssh/known_hosts:54
Password authentication is disabled to avoid man-in-the-middle attacks.
Keyboard-interactive authentication is disabled to avoid man-in-the-middle attacks.
Agent forwarding is disabled to avoid man-in-the-middle attacks.
X11 forwarding is disabled to avoid man-in-the-middle attacks.
Debian GNU/Linux 7

BeagleBoard.org Debian Image 2015-03-01

Support/FAQ: http://elinux.org/Beagleboard:BeagleBoneBlack_Debian

default username:password is [debian:temppwd]

Permission denied (publickey,password).
(reverse-i-search)`se': cd release/
taco:~ pkb$ sed -i -e 54d ~/.ssh/known_hosts
taco:~ pkb$

Or, if using the rmsshhost function, you can remove line 54 using the following command:

rmsshhost 54

Find File Differences in Two Directories

This one is handy when you have two directories (DIRA and DIRB) with a similar set of files and you want to determine if any of the files in DIRB are different than the files in DIRA. As an example, if you are looking for differences in your CSS files under the css directory (DIRA) with the css files in the 1.1.7 release found at ../1.1.7/css (DIRB).

[root@rice 1.1.4]# find css -type f | wc -l 
4 
[root@rice 1.1.4]# find css -type f | while read src; do cmp ${src} ../1.1.7/${src}; done
css/site.css ../1.1.7/css/site.css differ: byte 31, line 3
[root@rice 1.1.4]#

Modifying An ISO Disk Image for Booting

The example below mounts an iso disk image and copies both the "EFI" and "isolinux" directories to a Read / Write directory: "/DATA/nstboot/" for the purpose of modifying isolinux and EFI booting:

[root@shopper2 iso]# mount -o loop ./nst-30-11210.x86_64.iso /mnt/iso/;
[root@shopper2 iso]# cd /DATA/nstboot/;
[root@shopper2 iso]# cp -aR /mnt/iso/EFI .
[root@shopper2 iso]# cp -aR /mnt/iso/isolinux .
[root@shopper2 iso]# ls -al /DATA/nstboot/
total 16
drwxr-xr-x 4 root root 4096 Jan  3 09:14 .
drwxr-xr-x 9 root root 4096 Jan  3 09:08 ..
dr-xr-xr-x 3 root root 4096 Jul 16 09:10 EFI
dr-xr-xr-x 2 root root 4096 Jul 16 09:10 isolinux
[root@shopper2 iso]#
[root@shopper2 iso]# umount /mnt/iso;
[root@shopper2 iso]#

After making modifications, the following mkisofs command can be used to rebuild the ISO boot image for testing.

[root@shopper2 iso]# mkisofs -o /DATA/iso/nstboot.iso -b isolinux/isolinux.bin -J -R -l -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -eltorito-alt-boot -e isolinux/efiboot.img -no-emul-boot -graft-points -V "NST30-BOOT" /DATA/nstboot/;
[root@shopper2 iso]#
[root@shopper2 iso]# ls -al /DATA/iso/nstboot.iso;
-rw-r--r-- 1 root root 110659584 Jan  3 09:17 /DATA/iso/nstboot.iso
[root@shopper2 iso]#

Locate Command

The locate command is a linux utility which serves to find files on filesystems. It searches through a prebuilt database: "/var/lib/mlocate/mlocate.db" generated by the updatedb command or by a systemd service: "/usr/lib/systemd/system/mlocate-updatedb.service" and timer unit: "/usr/lib/systemd/system/mlocate-updatedb.timer" which is compressed using incremental encoding.

The example below uses the locate command to search for htop files using the regular expression: "/htop$"

[root@shopper2 ~]# locate --regexp '/htop$'
/etc/pcp/pmlogconf/tools/htop
/root/.config/htop
/usr/bin/htop
/usr/share/bash-completion/completions/htop
/usr/share/doc/htop
/usr/share/licenses/htop
/var/lib/pcp/config/pmlogconf/tools/htop

The output below demonstrates how to manually update the default searched database: "/var/lib/mlocate/mlocate.db" using the utility: "/usr/libexec/mlocate-run-updatedb"

[root@shopper2 ~]# ls -al /var/lib/mlocate/mlocate.db;
-rw-r----- 1 root slocate 13715680 Aug 16 20:17 /var/lib/mlocate/mlocate.db

[root@shopper2 ~]# /usr/libexec/mlocate-run-updatedb;

[root@shopper2 ~]# ls -al /var/lib/mlocate/mlocate.db;
-rw-r----- 1 root slocate 13715680 Aug 16 20:18 /var/lib/mlocate/mlocate.db

Ncat One Liners

Overview

Ncat is a similar tool to netcat provided by Nmap suite. Ncat features includes: ability to chain Ncats together, redirect both TCP and UDP ports to other sites, SSL support, and proxy connections via SOCKS4 or HTTP (CONNECT method) proxies (with optional proxy authentication as well).

Ncat always operates in one of two basic modes: connect mode and listen mode. In connect mode, Ncat initiates a connection (or sends UDP data) to a service that is listening somewhere. For those familiar with socket programming, connect mode is like using the connect function. In listen mode, Ncat waits for an incoming connection (or data receipt), like using the bind and listen functions. You can think of connect mode as “client” mode and listen mode as “server” mode.

To use Ncat in connect mode, run

ncat <host> [<port>]

<host> may be a hostname or IP address, and <port> is a port number. Listen mode is the same, with the addition of the --listen option (or its -l alias):

ncat --listen [<host>] [<port>] ncat -l [<host>] [<port>]

In listen mode, <host> controls the address on which Ncat listens; if you omit it, Ncat will bind to all local interfaces (INADDR_ANY). If the port number is omitted, Ncat uses its default port 31337. Typically only privileged (root) users may bind to a port number lower than 1024. A listening TCP server normally accepts only one connection and will exit after the client disconnects. Combined with the --keep-open option, Ncat accepts multiple concurrent connections up to the connection limit. With --keep-open (or -k for short), the server receives everything sent by any of its clients, and anything the server sends is sent to all of them. A UDP server will communicate with only one client (the first one to send it data), because in UDP there is no list of “connected” clients.

See the Ncat Basic Users' Guide for a detailed infomation.

By default, Ncat uses TCP. The option --udp or -u enables UDP instead, and --sctp enables SCTP. Ncat listens on both IPv4 and IPv6, and connects to either address family as well. The -6 option forces IPv6-only, and -4 forces IPv4-only. For a quick summary of options at any time, run ncat --help or man ncat.

Ncat As a Web Browser

After the connection type in "GET / HTTP/1.0" followed by two(2) enter key strokes.

[root@10.222.222.10 ~]# ncat -C www.openwrt.org 80;
GET / HTTP/1.0

HTTP/1.1 301 Moved Permanently
Server: nginx
Date: Mon, 10 Feb 2020 13:44:37 GMT
Content-Type: text/html
Content-Length: 178
Connection: close
Location: https://openwrt.org/


<html>
<head><title>301 Moved Permanently</title></head>
<body bgcolor="white">
<center><h1>301 Moved Permanently</h1></center>
<hr><center>nginx</center>
</body>
</html>
 

SMTP Connection

After the connection type in SMTP command (helo <domain>): "helo verizon.net" followed by one(1) enter key stroke.

[root@10.222.222.10 tmp]# ncat -C smtp.aol.com 587;
220 smtp.mail.yahoo.com ESMTP ready
helo verizon.net
250 smtp406.mail.bf1.yahoo.com Hello verizon.net [71.164.79.94])
^C
[root@10.222.222.10 tmp]#

Command Execution TCP/IP

Run a command with --exec using TCP/IP port: 30000 on host: 10.222.222.10 (i.e., Server Side). Execute a TCP/IP connection on host: 10.222.222.22 (i.e., Client Side) to 10.222.222.10:30000:

Server Side: 10.222.222.10

[root@10.222.222.10 ~]# ncat -l -k -p 30000 --exec "/bin/echo Hello.";

Check if TCP/IP port: 30000 is active on host: 10.222.222.10:

[root@10.222.222.10 ~]# netstat -tnap | grep 30000;
tcp        0      0 0.0.0.0:30000           0.0.0.0:*               LISTEN      6076/ncat           
tcp6       0      0 :::30000                :::*                    LISTEN      6076/ncat
          

Client Side: 10.222.222.22

[root@10.222.222.22 ~]# ncat 10.222.222.10 30000;
Hello.
^C
[root@10.222.222.22 ~]#

Command Execution UDP

Run a command with --exec using UDP port: 33333 on host: 10.222.222.10 (i.e., Server Side). Execute a UDP connection on host: 10.222.222.22 (i.e., Client Side) to 10.222.222.10:33333:

Server Side: 10.222.222.10

[root@10.222.222.10 ~]# ncat -l -u -k -p 33333 --exec "/bin/echo Hello.";

Check if UDP port: 33333 is active on host: 10.222.222.10:

[root@10.222.222.10 ~]# netstat -unap | grep 33333;
tcp        0      0 0.0.0.0:33333           0.0.0.0:*               LISTEN      968/ncat           
tcp6       0      0 :::33333                :::*                    LISTEN      968/ncat
          

Client Side: 10.222.222.22

[root@10.222.222.22 ~]# ncat -C -u 10.222.222.10 33333;
<enter>
Hello.
^C
[root@10.222.222.22 ~]#

Serial Over TCP/IP - A Remote Serial Stream (stty, ncat)

In this example we will used a GPS serial stream (4800 Baud) connected to USB-to-Serial adapter: "/dev/ttyUSB1" on host: "10.222.222.23" and use ncat to establish a TCP/IP listening socket on port: "22222". On host: "10.222.222.10" we will connect via TCP/IP to this service on host: "10.222.222.23".

On host: "10.222.222.23"

• First set the serial baud rate and any special settings for the USB-to-Serial device: "/dev/ttyUSB1" using the "stty" utility:

[root@10.222.222.23 ~]# stty -F /dev/ttyUSB1 4800 raw;

• Next establish the TCP/IP GPS service on port: "22222" via ncat:

[root@10.222.222.23 ~]# ncat -l 22222 > /dev/ttyUSB1 < /dev/ttyUSB1;

On host: "10.222.222.10"

• Connect to the TCP/IP GPS service on host: "10.222.222.23" using ncat:

[root@10.222.222.10 ~]# ncat 10.222.222.23 22222;
$PGRME,14.4,M,21.0,M,25.4,M*1F
$GPRMC,132904,A,4241.6671,N,07351.6808,W,000.0,239.2,110220,014.2,W,A*18
$GPGGA,132904,4241.6671,N,07351.6808,W,1,04,2.1,109.6,M,-33.5,M,,*7F
$GPGSA,M,2,10,,12,,,24,,,32,,,,2.4,2.1,1.0*3E
$GPGSV,3,2,11,20,48,150,00,24,33,051,32,25,25,137,00,31,14,218,00*78
$PGRME,14.4,M,21.0,M,25.4,M*1F
$GPRMC,132905,A,4241.6673,N,07351.6809,W,000.0,239.2,110220,014.2,W,A*1A
$GPGGA,132905,4241.6673,N,07351.6809,W,1,04,2.1,110.1,M,-33.5,M,,*72
$GPGSA,M,2,10,,12,,,24,,,32,,,,2.4,2.1,1.0*3E
$GPGSV,3,3,11,32,59,297,37,34,00,000,00,35,00,000,00*4D
^C
[root@10.222.222.10 ~]#

Serial Over TCP/IP - A Remote Serial Login Console (stty, ncat, socat, minicom)

In this example we will used a Raspberry PI 4 serial console connection (115200 Baud) attached to USB-to-Serial adapter: "/dev/ttyUSB0" on host: "172.16.1.245" and use ncat to establish a TCP/IP listening socket on port: "22222". On host: "172.16.1.71" we will connect via TCP/IP to this console service on remote host: "172.16.1.245". The socat utility and the terminal emulator "minicom" application will be used to establish an interactive session to the remote Raspberry Pi 4 serial login console.

On host: "172.16.1.245"

• First set the serial baud rate and any special settings for the USB-to-Serial device: "/dev/ttyUSB0" using the "stty" utility:

[root@172.16.1.245 ~]# stty -F /dev/ttyUSB0 115200 raw;

• Next establish the TCP/IP Raspberry Pi 4 serial console service on port: "22222" via ncat and put the process in the background:

[root@172.16.1.245 ~]# ncat -l 22222 > /dev/ttyUSB0 < /dev/ttyUSB0 &

On host: "172.16.1.71"

• Connect to the TCP/IP Raspberry Pi 4 serial console service on host: "172.16.1.245", port: "22222" using socat and put the process in the background. The pseudo terminal: "/dev/ttyV0" will be created by socat for attaching minicom.

[root@172.16.1.245 ~]# socat pty,link=/dev/ttyV0 tcp:172.16.1.245:22222 &

• Create a minicom configuration in file: "/etc/minirc.ttyV0":

[root@172.16.1.71]# cat /etc/minirc.ttyV0
#
# Raspbery Pi 4 Serial Login Console
pu port             /dev/ttyV0
pu baudrate         115200
pu bits             8
pu parity           N
pu stopbits         1
pu rtscts           No
pu xonxoff          No
#
# Disable modem initialization values...
pu minit
pu mreset
pu mdialpre
pu mdialsuf
pu mdialpre2
pu mdialsuf2
pu mdialpre3
pu mdialsuf3
pu mhangup
pu mdialcan

• Next attach minicom to the newly created pseudo terminal: "/dev/V0" - An interactive serial login console session to a Raspberry Pi 4 attached to remote system: "172.16.1.245". The user: "pi" will be used for logging in.

[root@172.16.1.71]# minicom -w -c on -t xterm ttyV0;
Welcome to minicom 2.7.1

OPTIONS: I18n 
Compiled on Feb 10 2020, 00:00:00.
Port /dev/ttyV0, 12:27:47

Press CTRL-A Z for help on special keys

rpi4 login: pi
Password: ************ 
Last login: Fri Oct  2 11:34:47 EDT 2020 on ttyS0
Linux rpi4 5.4.51-v7l+ #1327 SMP Thu Jul 23 11:04:39 BST 2020 armv7l

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.

pi@rpi4:~$ lscpu 
Architecture:        armv7l
Byte Order:          Little Endian
CPU(s):              4
On-line CPU(s) list: 0-3
Thread(s) per core:  1
Core(s) per socket:  4
Socket(s):           1
Vendor ID:           ARM
Model:               3
Model name:          Cortex-A72
Stepping:            r0p3
CPU max MHz:         1500.0000
CPU min MHz:         600.0000
BogoMIPS:            108.00
Flags:               half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32
pi@rpi4:~$ exit
logout

Raspbian GNU/Linux 10 rpi4 ttyS0

rpi4 login:

Tunneling UDP Traffic Through An SSH Connection

See article: Tunneling UDP Traffic Through An SSH Connection