16.6. Communications Commands. Comtrol DeviceMaster Software Development Kit

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Advanced Bash-Scripting Guide

make

Utility for building and compiling binary packages. This can also be used for any set of operations triggered by incremental changes in source files.

The make command checks a

Makefile

, a list of file dependencies and operations to be carried out.

The make utility is, in effect, a powerful scripting language similar in many ways to Bash, but with the capability of recognizing dependencies. For in-depth coverage of this useful tool set, see the GNU software documentation site.

install

Special purpose file copying command, similar to cp, but capable of setting permissions and attributes

of the copied files. This command seems tailormade for installing software packages, and as such it shows up frequently in

Makefiles

(in the

make install :

section). It could likewise prove useful in installation scripts.

dos2unix

This utility, written by Benjamin Lin and collaborators, converts DOS-formatted text files (lines

terminated by CR-LF) to UNIX format (lines terminated by LF only), and vice-versa.

ptx

The ptx [targetfile] command outputs a permuted index (cross-reference list) of the targetfile. This may be further filtered and formatted in a pipe, if necessary.

more

, less

Pagers that display a text file or stream to

stdout

, one screenful at a time. These may be used to filter the output of

stdout

. . . or of a script.

An interesting application of more is to "test drive" a command sequence, to forestall potentially unpleasant consequences.

ls /home/bozo | awk '{print "rm -rf " $1}' | more

# ^^^^

# Testing the effect of the following (disastrous) command-line:

# ls /home/bozo | awk '{print "rm -rf " $1}' | sh

# Hand off to the shell to execute . . . ^^

The less pager has the interesting property of doing a formatted display of man page source. See

Example A-39.

16.6. Communications Commands

Certain of the following commands find use in network data transfer and analysis, as well as in chasing spammers.

Information and Statistics host

Searches for information about an Internet host by name or IP address, using DNS.

bash$

host surfacemail.com

surfacemail.com. has address 202.92.42.236

ipcalc

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Displays IP information for a host. With the

-h

option, ipcalc does a reverse DNS lookup, finding the name of the host (server) from the IP address.

bash$

ipcalc -h 202.92.42.236

HOSTNAME=surfacemail.com

nslookup

Do an Internet "name server lookup" on a host by IP address. This is essentially equivalent to ipcalc

-h

or dig -x . The command may be run either interactively or noninteractively, i.e., from within a script.

The nslookup command has allegedly been "deprecated," but it is still useful.

bash$

nslookup -sil 66.97.104.180

nslookup kuhleersparnis.ch

Server: 135.116.137.2

Address: 135.116.137.2#53

Non-authoritative answer:

Name: kuhleersparnis.ch

dig

omain Information Groper. Similar to nslookup, dig does an Internet name server lookup on a host.

May be run from the command-line or from within a script.

Some interesting options to dig are

+time=N

for setting a query timeout to

seconds,

+nofail

for continuing to query servers until a reply is received, and

-x

for doing a reverse address lookup.

Compare the output of dig -x with ipcalc -h and nslookup.

bash$

dig -x 81.9.6.2

;; Got answer:

;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 11649

;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:

;2.6.9.81.in-addr.arpa. IN PTR

;; AUTHORITY SECTION:

6.9.81.in-addr.arpa. 3600 IN SOA ns.eltel.net. noc.eltel.net.

2002031705 900 600 86400 3600

;; Query time: 537 msec

;; SERVER: 135.116.137.2#53(135.116.137.2)

;; WHEN: Wed Jun 26 08:35:24 2002

;; MSG SIZE rcvd: 91

Example 16-40. Finding out where to report a spammer

#!/bin/bash

# spam-lookup.sh: Look up abuse contact to report a spammer.

# Thanks, Michael Zick.

# Check for command-line arg.

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ARGCOUNT=1

E_WRONGARGS=85 if [ $# -ne "$ARGCOUNT" ] then

echo "Usage: `basename $0` domain-name"

exit $E_WRONGARGS fi dig +short $1.contacts.abuse.net -c in -t txt

# Also try:

# dig +nssearch $1

# Tries to find "authoritative name servers" and display SOA records.

# The following also works:

# whois -h whois.abuse.net $1

# ^^ ^^^^^^^^^^^^^^^ Specify host.

# Can even lookup multiple spammers with this, i.e."

# whois -h whois.abuse.net $spamdomain1 $spamdomain2 . . .

# Exercise:

# --------

# Expand the functionality of this script

#+ so that it automatically e-mails a notification

#+ to the responsible ISP's contact address(es).

# Hint: use the "mail" command.

exit $?

# spam-lookup.sh chinatietong.com

# A known spam domain.

# "[email protected]"

# For a more elaborate version of this script,

#+ see the SpamViz home page, http://www.spamviz.net/index.html.

Example 16-41. Analyzing a spam domain

#! /bin/bash

# is-spammer.sh: Identifying spam domains

# $Id: is-spammer, v 1.4 2004/09/01 19:37:52 mszick Exp $

# Above line is RCS ID info.

# This is a simplified version of the "is_spammer.bash

#+ script in the Contributed Scripts appendix.

# is-spammer <domain.name>

# Uses an external program: 'dig'

# Tested with version: 9.2.4rc5

# Uses functions.

# Uses IFS to parse strings by assignment into arrays.

# And even does something useful: checks e-mail blacklists.

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# Use the domain.name(s) from the text body:

# http://www.good_stuff.spammer.biz/just_ignore_everything_else

# ^^^^^^^^^^^

# Or the domain.name(s) from any e-mail address:

# [email protected]

# as the only argument to this script.

#(PS: have your Inet connection running)

# So, to invoke this script in the above two instances:

# is-spammer.sh spammer.biz

# Whitespace == :Space:Tab:Line Feed:Carriage Return:

WSP_IFS=$'\x20'$'\x09'$'\x0A'$'\x0D'

# No Whitespace == Line Feed:Carriage Return

No_WSP=$'\x0A'$'\x0D'

# Field separator for dotted decimal ip addresses

ADR_IFS=${No_WSP}'.'

# Get the dns text resource record.

# get_txt <error_code> <list_query> get_txt() {

# Parse $1 by assignment at the dots.

local -a dns

IFS=$ADR_IFS

dns=( $1 )

IFS=$WSP_IFS

if [ "${dns[0]}" == '127' ]

then

# See if there is a reason.

echo $(dig +short $2 -t txt)

}

# Get the dns address resource record.

# chk_adr <rev_dns> <list_server> chk_adr() {

local reply

local server

local reason

server=${1}${2}

reply=$( dig +short ${server} )

# If reply might be an error code . . .

if [ ${#reply} -gt 6 ]

then

reason=$(get_txt ${reply} ${server} )

reason=${reason:-${reply}}

echo ${reason:-' not blacklisted.'}

}

# Need to get the IP address from the name.

echo 'Get address of: '$1 ip_adr=$(dig +short $1) dns_reply=${ip_adr:-' no answer '}

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# A valid reply is at least 4 digits plus 3 dots.

if [ ${#ip_adr} -gt 6 ] then

echo

declare query

# Parse by assignment at the dots.

declare -a dns

IFS=$ADR_IFS

dns=( ${ip_adr} )

IFS=$WSP_IFS

# Reorder octets into dns query order.

rev_dns="${dns[3]}"'.'"${dns[2]}"'.'"${dns[1]}"'.'"${dns[0]}"'.'

# See: http://www.spamhaus.org (Conservative, well maintained)

echo -n 'spamhaus.org says: '

echo $(chk_adr ${rev_dns} 'sbl-xbl.spamhaus.org')

# See: http://ordb.org (Open mail relays)

echo -n ' ordb.org says: '

echo $(chk_adr ${rev_dns} 'relays.ordb.org')

# See: http://www.spamcop.net/ (You can report spammers here)

echo -n ' spamcop.net says: '

echo $(chk_adr ${rev_dns} 'bl.spamcop.net')

# # # other blacklist operations # # #

# See: http://cbl.abuseat.org.

echo -n ' abuseat.org says: '

echo $(chk_adr ${rev_dns} 'cbl.abuseat.org')

# See: http://dsbl.org/usage (Various mail relays)

echo

echo 'Distributed Server Listings'

echo -n ' list.dsbl.org says: '

echo $(chk_adr ${rev_dns} 'list.dsbl.org')

echo -n ' multihop.dsbl.org says: '

echo $(chk_adr ${rev_dns} 'multihop.dsbl.org')

echo -n 'unconfirmed.dsbl.org says: '

echo $(chk_adr ${rev_dns} 'unconfirmed.dsbl.org') else

echo

echo 'Could not use that address.' fi exit 0

# Exercises:

# --------

# 1) Check arguments to script,

# and exit with appropriate error message if necessary.

# 2) Check if on-line at invocation of script,

# and exit with appropriate error message if necessary.

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# 3) Substitute generic variables for "hard-coded" BHL domains.

# 4) Set a time-out for the script using the "+time=" option

to the 'dig' command.

For a much more elaborate version of the above script, see Example A-28.

traceroute

Trace the route taken by packets sent to a remote host. This command works within a LAN, WAN, or over the Internet. The remote host may be specified by an IP address. The output of this command

may be filtered by grep or sed in a pipe.

bash$

traceroute 81.9.6.2

traceroute to 81.9.6.2 (81.9.6.2), 30 hops max, 38 byte packets

1 tc43.xjbnnbrb.com (136.30.178.8) 191.303 ms 179.400 ms 179.767 ms

2 or0.xjbnnbrb.com (136.30.178.1) 179.536 ms 179.534 ms 169.685 ms

3 192.168.11.101 (192.168.11.101) 189.471 ms 189.556 ms *

...

ping

Broadcast an

ICMP ECHO_REQUEST

packet to another machine, either on a local or remote network. This is a diagnostic tool for testing network connections, and it should be used with caution.

bash$

ping localhost

PING localhost.localdomain (127.0.0.1) from 127.0.0.1 : 56(84) bytes of data.

64 bytes from localhost.localdomain (127.0.0.1): icmp_seq=0 ttl=255 time=709 usec

64 bytes from localhost.localdomain (127.0.0.1): icmp_seq=1 ttl=255 time=286 usec

--- localhost.localdomain ping statistics ---

2 packets transmitted, 2 packets received, 0% packet loss

round-trip min/avg/max/mdev = 0.286/0.497/0.709/0.212 ms

A successful ping returns an exit status of 0. This can be tested for in a script.

HNAME=news-15.net # Notorious spammer.

# HNAME=$HOST # Debug: test for localhost.

count=2 # Send only two pings.

if [[ `ping -c $count "$HNAME"` ]] then

echo ""$HNAME" still up and broadcasting spam your way." else

echo ""$HNAME" seems to be down. Pity." fi

whois

Perform a DNS (Domain Name System) lookup. The

-h

option permits specifying which particular

whois server to query. See Example 4-6 and Example 16-40.

finger

Retrieve information about users on a network. Optionally, this command can display a user's

~/.plan

~/.project

, and

~/.forward

files, if present.

bash$

finger

bozo Bozo Bozeman tty1 8 Jun 25 16:59 (:0)

bozo Bozo Bozeman ttyp0 Jun 25 16:59 (:0.0)

bozo Bozo Bozeman ttyp1 Jun 25 17:07 (:0.0)

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finger bozo

Directory: /home/bozo Shell: /bin/bash

Office: 2355 Clown St., 543-1234

On since Fri Aug 31 20:13 (MST) on tty1 1 hour 38 minutes idle

On since Fri Aug 31 20:13 (MST) on pts/0 12 seconds idle

On since Fri Aug 31 20:13 (MST) on pts/1

On since Fri Aug 31 20:31 (MST) on pts/2 1 hour 16 minutes idle

Mail last read Tue Jul 3 10:08 2007 (MST)

No Plan.

Out of security considerations, many networks disable finger and its associated daemon. [81]

chfn vrfy

Change information disclosed by the finger command.

Verify an Internet e-mail address.

This command seems to be missing from newer Linux distros.

Remote Host Access sx

, rx

The sx and rx command set serves to transfer files to and from a remote host using the xmodem protocol. These are generally part of a communications package, such as minicom.

, rz

The sz and rz command set serves to transfer files to and from a remote host using the zmodem protocol. Zmodem has certain advantages over xmodem, such as faster transmission rate and resumption of interrupted file transfers. Like sx and rx, these are generally part of a communications package.

ftp

Utility and protocol for uploading / downloading files to or from a remote host. An ftp session can be

automated in a script (see Example 19-6 and Example A-4).

uucp

, uux, cu

uucp

: UNIX to UNIX copy. This is a communications package for transferring files between UNIX servers. A shell script is an effective way to handle a uucp command sequence.

Since the advent of the Internet and e-mail, uucp seems to have faded into obscurity, but it still exists and remains perfectly workable in situations where an Internet connection is not available or appropriate. The advantage of uucp is that it is fault-tolerant, so even if there is a service interruption the copy operation will resume where it left off when the connection is restored.

---

uux

: UNIX to UNIX execute. Execute a command on a remote system. This command is part of the

uucp

package.

---

: Call Up a remote system and connect as a simple terminal. It is a sort of dumbed-down version of

telnet. This command is part of the uucp package.

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telnet

Utility and protocol for connecting to a remote host.

The telnet protocol contains security holes and should therefore probably be avoided.

Its use within a shell script is not recommended.

wget

The wget utility noninteractively retrieves or downloads files from a Web or ftp site. It works well in a script.

wget -p http://www.xyz23.com/file01.html

# The -p or --page-requisite option causes wget to fetch all files

#+ required to display the specified page.

wget -r ftp://ftp.xyz24.net/~bozo/project_files/ -O $SAVEFILE

# The -r option recursively follows and retrieves all links

#+ on the specified site.

wget -c ftp://ftp.xyz25.net/bozofiles/filename.tar.bz2

# The -c option lets wget resume an interrupted download.

# This works with ftp servers and many HTTP sites.

Example 16-42. Getting a stock quote

#!/bin/bash

# quote-fetch.sh: Download a stock quote.

E_NOPARAMS=86 if [ -z "$1" ] # Must specify a stock (symbol) to fetch.

then echo "Usage: `basename $0` stock-symbol"

exit $E_NOPARAMS fi stock_symbol=$1 file_suffix=.html

# Fetches an HTML file, so name it appropriately.

URL='http://finance.yahoo.com/q?s='

# Yahoo finance board, with stock query suffix.

# ----------------------------------------------------------wget -O ${stock_symbol}${file_suffix} "${URL}${stock_symbol}"

# -----------------------------------------------------------

# To look up stuff on http://search.yahoo.com:

# -----------------------------------------------------------

# URL="http://search.yahoo.com/search?fr=ush-news&p=${query}"

# wget -O "$savefilename" "${URL}"

# -----------------------------------------------------------

# Saves a list of relevant URLs.

exit $?

# Exercises:

# ---------

# 1) Add a test to ensure the user running the script is on-line.

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lynx

Advanced Bash-Scripting Guide

# (Hint: parse the output of 'ps -ax' for "ppp" or "connect."

# 2) Modify this script to fetch the local weather report,

#+ taking the user's zip code as an argument.

-dump

option) to retrieve a file from a Web or ftp site noninteractively.

rlogin

Remote login

, initates a session on a remote host. This command has security issues, so use ssh

instead.

rsh

lynx -dump http://www.xyz23.com/file01.html >$SAVEFILE

With the

-traversal

option, lynx starts at the HTTP URL specified as an argument, then "crawls" through all links located on that particular server. Used together with the

-crawl

option, outputs page text to a log file.

Remote shell

, executes command(s) on a remote host. This has security issues, so use ssh instead.

rcp

Remote copy

, copies files between two different networked machines.

rsync

Remote synchronize

, updates (synchronizes) files between two different networked machines.

bash$

rsync -a ~/sourcedir/*txt /node1/subdirectory/

Example 16-43. Updating FC4

#!/bin/bash

# fc4upd.sh

# Script author: Frank Wang.

# Slight stylistic modifications by ABS Guide author.

# Used in ABS Guide with permission.

# Download Fedora Core 4 update from mirror site using rsync.

# Should also work for newer Fedora Cores -- 5, 6, . . .

# Only download latest package if multiple versions exist,

#+ to save space.

URL=rsync://distro.ibiblio.org/fedora-linux-core/updates/

# URL=rsync://ftp.kddilabs.jp/fedora/core/updates/

# URL=rsync://rsync.planetmirror.com/fedora-linux-core/updates/

DEST=${1:-/var/www/html/fedora/updates/}

LOG=/tmp/repo-update-$(/bin/date +%Y-%m-%d).txt

PID_FILE=/var/run/${0##*/}.pid

E_RETURN=85 # Something unexpected happened.

# General rsync options

# -r: recursive download

# -t: reserve time

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# -v: verbose

OPTS="-rtv --delete-excluded --delete-after --partial"

# rsync include pattern

# Leading slash causes absolute path name match.

INCLUDE=(

"/4/i386/kde-i18n-Chinese*"

# ^ ^

# Quoting is necessary to prevent globbing.

)

# rsync exclude pattern

# Temporarily comment out unwanted pkgs using "#" . . .

EXCLUDE=(

/testing

/4/SRPMS

/4/ppc

/4/x86_64

/4/i386/debug

"/4/i386/kde-i18n-*"

"/4/i386/openoffice.org-langpack-*"

"/4/i386/*i586.rpm"

"/4/i386/GFS-*"

"/4/i386/cman-*"

"/4/i386/dlm-*"

"/4/i386/gnbd-*"

"/4/i386/kernel-smp*"

# "/4/i386/kernel-xen*"

# "/4/i386/xen-*"

) init () {

# Let pipe command return possible rsync error, e.g., stalled network.

set -o pipefail # Newly introduced in Bash, version 3.

TMP=${TMPDIR:-/tmp}/${0##*/}.$$ # Store refined download list.

trap "{

rm -f $TMP 2>/dev/null

}" EXIT # Clear temporary file on exit.

} check_pid () {

# Check if process exists.

if [ -s "$PID_FILE" ]; then

echo "PID file exists. Checking ..."

PID=$(/bin/egrep -o "^[[:digit:]]+" $PID_FILE)

if /bin/ps --pid $PID &>/dev/null; then

echo "Process $PID found. ${0##*/} seems to be running!"

/usr/bin/logger -t ${0##*/} \

"Process $PID found. ${0##*/} seems to be running!"

exit $E_RETURN

echo "Process $PID not found. Start new process . . ."

}

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# Set overall file update range starting from root or $URL,

#+ according to above patterns.

set_range () {

include=

exclude=

for p in "${INCLUDE[@]}"; do

include="$include --include \"$p\""

done

for p in "${EXCLUDE[@]}"; do

exclude="$exclude --exclude \"$p\""

done

}

# Retrieve and refine rsync update list.

get_list () {

echo $$ > $PID_FILE || {

echo "Can't write to pid file $PID_FILE"

exit $E_RETURN

}

echo -n "Retrieving and refining update list . . ."

# Retrieve list -- 'eval' is needed to run rsync as a single command.

# $3 and $4 is the date and time of file creation.

# $5 is the full package name.

previous=

pre_file=

pre_date=0

eval /bin/nice /usr/bin/rsync \

-r $include $exclude $URL | \

egrep '^dr.x|^-r' | \

awk '{print $3, $4, $5}' | \

sort -k3 | \

{ while read line; do

# Get seconds since epoch, to filter out obsolete pkgs.

cur_date=$(date -d "$(echo $line | awk '{print $1, $2}')" +%s)

# echo $cur_date

# Get file name.

cur_file=$(echo $line | awk '{print $3}')

# echo $cur_file

# Get rpm pkg name from file name, if possible.

if [[ $cur_file == *rpm ]]; then

pkg_name=$(echo $cur_file | sed -r -e \

's/(^([^_-]+[_-])+)[[:digit:]]+\..*[_-].*$/\1/')

else

pkg_name=

# echo $pkg_name

if [ -z "$pkg_name" ]; then # If not a rpm file,

echo $cur_file >> $TMP #+ then append to download list.

elif [ "$pkg_name" != "$previous" ]; then # A new pkg found.

echo $pre_file >> $TMP # Output latest file.

previous=$pkg_name # Save current.

pre_date=$cur_date

pre_file=$cur_file

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elif [ "$cur_date" -gt "$pre_date" ]; then

# If same pkg, but newer,

pre_date=$cur_date #+ then update latest pointer.

pre_file=$cur_file

done

echo $pre_file >> $TMP # TMP contains ALL

#+ of refined list now.

# echo "subshell=$BASH_SUBSHELL"

} # Bracket required here to let final "echo $pre_file >> $TMP"

# Remained in the same subshell ( 1 ) with the entire loop.

RET=$? # Get return code of the pipe command.

[ "$RET" -ne 0 ] && {

echo "List retrieving failed with code $RET"

exit $E_RETURN

}

echo "done"; echo

}

# Real rsync download part.

get_file () {

echo "Downloading..."

/bin/nice /usr/bin/rsync \

$OPTS \

--filter "merge,+/ $TMP" \

--exclude '*' \

$URL $DEST \

| /usr/bin/tee $LOG

RET=$?

# --filter merge,+/ is crucial for the intention.

# + modifier means include and / means absolute path.

# Then sorted list in $TMP will contain ascending dir name and

#+ prevent the following --exclude '*' from "shortcutting the circuit."

echo "Done"

rm -f $PID_FILE 2>/dev/null

return $RET

}

# -------

# Main init check_pid set_range get_list get_file

RET=$?

# ------if [ "$RET" -eq 0 ]; then

/usr/bin/logger -t ${0##*/} "Fedora update mirrored successfully." else

/usr/bin/logger -t ${0##*/} \

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ssh

Advanced Bash-Scripting Guide

"Fedora update mirrored with failure code: $RET" fi exit $RET

stdin

. To remedy this, pass ssh either the

-n

-f

option.

Thanks, Jason Bechtel, for pointing this out.

scp

Secure copy

, similar in function to rcp, copies files between two different networked machines, but does so using authentication, and with a security level similar to ssh.

Local Network write

This is a utility for terminal-to-terminal communication. It allows sending lines from your terminal

(console or xterm) to that of another user. The mesg command may, of course, be used to disable

write access to a terminal

Since write is interactive, it would not normally find use in a script.

netconfig

A command-line utility for configuring a network adapter (using DHCP). This command is native to

Red Hat centric Linux distros.

Mail mail

Send or read e-mail messages.

This stripped-down command-line mail client works fine as a command embedded in a script.

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Example 16-45. A script that mails itself

#!/bin/sh

# self-mailer.sh: Self-mailing script adr=${1:-`whoami`} # Default to current user, if not specified.

# Typing 'self-mailer.sh [email protected]'

#+ sends this script to that addressee.

# Just 'self-mailer.sh' (no argument) sends the script

#+ to the person invoking it, for example, [email protected].

# For more on the ${parameter:-default} construct,

#+ see the "Parameter Substitution" section

#+ of the "Variables Revisited" chapter.

# ============================================================================

cat $0 | mail -s "Script \"`basename $0`\" has mailed itself to you." "$adr"

# ============================================================================

# --------------------------------------------

# Greetings from the self-mailing script.

# A mischievous person has run this script,

#+ which has caused it to mail itself to you.

# Apparently, some people have nothing better

#+ to do with their time.

# -------------------------------------------echo "At `date`, script \"`basename $0`\" mailed to "$adr"." exit 0

# Note that the "mailx" command (in "send" mode) may be substituted

#+ for "mail" ... but with somewhat different options.

mailto

Similar to the mail command, mailto sends e-mail messages from the command-line or in a script.

However, mailto also permits sending MIME (multimedia) messages.

mailstats

Show mail statistics. This command may be invoked only by root.

root#

mailstats

Statistics from Tue Jan 1 20:32:08 2008

M msgsfr bytes_from msgsto bytes_to msgsrej msgsdis msgsqur Mailer

4 1682 24118K 0 0K 0 0 0 esmtp

9 212 640K 1894 25131K 0 0 0 local

=====================================================================

T 1894 24758K 1894 25131K 0 0 0

C 414 0

vacation

This utility automatically replies to e-mails that the intended recipient is on vacation and temporarily unavailable. It runs on a network, in conjunction with sendmail, and is not applicable to a dial-up

POPmail account.

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