Archive | Bash Scripting

Loop over lines in shell pipeline

By admin on February 16, 2018 in Bash Scripting, Linux

To loop over a list of line do this:

ls -al | while IFS= read -r line ; do echo $line; done

1	ls -al \| while IFS= read -r line ; do echo $line; done

Convert newlines to spaces

By admin on February 16, 2018 in Bash Scripting, Linux

TR can be used to convert a list of items from one per line to space separated with this:

tr '\r\n' ' '

1	tr '\r\n' ' '

Get IP Address In A Script

By admin on January 24, 2017 in Bash Scripting, Linux

Recently needed a good way to fetch the IP address of each interface within a script. Tried things like:

ifconfig  | grep 'inet addr:'| grep -v '127.0.0.1' | cut -d: -f2 | awk '{ print $1}'

1	ifconfig \| grep 'inet addr:'\| grep -v '127.0.0.1' \| cut -d: -f2 \| awk '{ print $1}'

and

/sbin/ifconfig | sed -n '2 p' | awk '{print $3}'

1	/sbin/ifconfig \| sed -n '2 p' \| awk '{print $3}'

But this is fairly ugly. So I tried:

hostname -I

1	hostname -I

This gives a list of IP addresses but they are un-ordered so I can’t guarantee which address goes with which interface. Here’s one using “ip addr”:

ip=$(ip -f inet -o addr show eth0|cut -d\  -f 7 | cut -d/ -f 1)

1	ip=$(ip -f inet -o addr show eth0\|cut -d\ -f 7 \| cut -d/ -f 1)

Still very messy. Finally, found the “ifdata” command which is part of the “moreutils” package. First make sure “moreutils” is installed with:

yum -y install moreutils

1	yum -y install moreutils

Now you can query for a wide range of different information:

Usage: ifdata [options] iface
     -e   Reports interface existence via return code
     -p   Print out the whole config of iface
    -pe   Print out yes or no according to existence
    -pa   Print out the address
    -pn   Print netmask
    -pN   Print network address
    -pb   Print broadcast
    -pm   Print mtu
    -ph   Print out the hardware address
    -pf   Print flags
    -si   Print all statistics on input
   -sip   Print # of in packets
   -sib   Print # of in bytes
   -sie   Print # of in errors
   -sid   Print # of in drops
   -sif   Print # of in fifo overruns
   -sic   Print # of in compress
   -sim   Print # of in multicast
    -so   Print all statistics on output
   -sop   Print # of out packets
   -sob   Print # of out bytes
   -soe   Print # of out errors
   -sod   Print # of out drops
   -sof   Print # of out fifo overruns
   -sox   Print # of out collisions
   -soc   Print # of out carrier loss
   -som   Print # of out multicast
  -bips   Print # of incoming bytes per second
  -bops   Print # of outgoing bytes per second

Usage: ifdata [options] iface

-e Reports interface existence via return code

-p Print out the whole config of iface

-pe Print out yes or no according to existence

-pa Print out the address

-pn Print netmask

-pN Print network address

-pb Print broadcast

-pm Print mtu

-ph Print out the hardware address

-pf Print flags

-si Print all statistics on input

-sip Print # of in packets

-sib Print # of in bytes

-sie Print # of in errors

-sid Print # of in drops

-sif Print # of in fifo overruns

-sic Print # of in compress

-sim Print # of in multicast

-so Print all statistics on output

-sop Print # of out packets

-sob Print # of out bytes

-soe Print # of out errors

-sod Print # of out drops

-sof Print # of out fifo overruns

-sox Print # of out collisions

-soc Print # of out carrier loss

-som Print # of out multicast

-bips Print # of incoming bytes per second

-bops Print # of outgoing bytes per second

So here are some examples:

[root@host]# ifdata -pa eth0
10.210.160.53

[root@host]# ifdata -pa eth0
10.210.160.53

[root@host]# ifdata -pn eth0
255.255.224.0

[root@host]# ifdata -sip eth0
1622384587

[root@host]# ifdata -bops eth0
896

[root@host]# ifdata -pa eth0

10.210.160.53

[root@host]# ifdata -pa eth0

10.210.160.53

[root@host]# ifdata -pn eth0

255.255.224.0

[root@host]# ifdata -sip eth0

1622384587

[root@host]# ifdata -bops eth0

896

Overall this is much cleaner and more reliable then the earlier approaches.

maxclients.sh Script For Apache

By admin on May 3, 2014 in Apache, Bash Scripting

This script attempts to look at Apache memory usage and recommend a stable setting for MaxClients.

#!/bin/bash

PROCNAME=httpd
PARENTPIDS=`comm -12 <(ps -C $PROCNAME -o ppid | sort -u) <(ps -C $PROCNAME -o pid | sort -u)`

for ParPID in $PARENTPIDS; do
  SUM=0
  COUNT=0
  for x in `ps f --ppid $ParPID -o rss | tail -n +2`; do
    SUM=$(( $SUM + $x ))
    COUNT=$(( $COUNT + 1 ))
  done

  MEMPP=$(( $SUM / $COUNT / 1024 ))
  FREERAM=$(( `free | tail -2 | head -1 | awk '{print $4}'` / 1024 ))
  APACHERAM=$(( $SUM / 1024 ))
  APACHEMAX=$(( $APACHERAM + $FREERAM ))

  (
  echo
  echo "Info for the following parent apache process:"
  echo "  "`ps f --pid $ParPID -o command | tail -n +2`
  echo
  echo "Current # of apache processes:        $COUNT"
  echo "Average memory per apache process:    $MEMPP MB"
  echo "Free RAM (including cache & buffers): $FREERAM MB"
  echo "RAM currently in use by apache:       $APACHERAM MB"
  echo "Max RAM available to apache:          $APACHEMAX MB"
  echo
  echo "Theoretical maximum MaxClients:  $(( $APACHEMAX / $MEMPP ))"
  echo "Recommended MaxClients:          $(( $APACHEMAX / 10 * 9 / $MEMPP ))"
  echo
  )
done

#!/bin/bash

PROCNAME=httpd

PARENTPIDS=`comm -12 <(ps -C $PROCNAME -o ppid | sort -u) <(ps -C $PROCNAME -o pid | sort -u)`

for ParPID in $PARENTPIDS; do

SUM=0

COUNT=0

for x in `ps f --ppid $ParPID -o rss | tail -n +2`; do

SUM=$(( $SUM + $x ))

COUNT=$(( $COUNT + 1 ))

done

MEMPP=$(( $SUM / $COUNT / 1024 ))

FREERAM=$(( `free | tail -2 | head -1 | awk '{print $4}'` / 1024 ))

APACHERAM=$(( $SUM / 1024 ))

APACHEMAX=$(( $APACHERAM + $FREERAM ))

(

echo

echo "Info for the following parent apache process:"

echo " "`ps f --pid $ParPID -o command | tail -n +2`

echo

echo "Current # of apache processes: $COUNT"

echo "Average memory per apache process: $MEMPP MB"

echo "Free RAM (including cache & buffers): $FREERAM MB"

echo "RAM currently in use by apache: $APACHERAM MB"

echo "Max RAM available to apache: $APACHEMAX MB"

echo

echo "Theoretical maximum MaxClients: $(( $APACHEMAX / $MEMPP ))"

echo "Recommended MaxClients: $(( $APACHEMAX / 10 * 9 / $MEMPP ))"

echo

)

done

getpass.sh Bash Script

By admin on May 3, 2014 in Bash Scripting

Simple bash script for generating random passwords. We didn’t write this and don’t know exactly where it came from.

#!/bin/bash

MATRIX="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
LENGTH=$1

while [ "${n:=1}" -le "$LENGTH" ]
# ==> Recall that := is "default substitution" operator.
# ==> So, if 'n' has not been initialized, set it to 1.
do
       PASS="$PASS${MATRIX:$(($RANDOM%${#MATRIX})):1}"
       # ==> Very clever, but tricky.

       # ==> Starting from the innermost nesting...
       # ==> ${#MATRIX} returns length of array MATRIX.

       # ==> $RANDOM%${#MATRIX} returns random number between 1
       # ==> and [length of MATRIX] - 1.

       # ==> ${MATRIX:$(($RANDOM%${#MATRIX})):1}
       # ==> returns expansion of MATRIX at random position, by length 1.
       # ==> See {var:pos:len} parameter substitution in Chapter 9.
       # ==> and the associated examples.

       # ==> PASS=... simply pastes this result onto previous PASS (concatenation).

       # ==> To visualize this more clearly, uncomment the following line
       #                 echo "$PASS"
       # ==> to see PASS being built up,
       # ==> one character at a time, each iteration of the loop.

       let n+=1
       # ==> Increment 'n' for next pass.
done

echo -n "$PASS"      # ==> Or, redirect to a file, as desired.

exit 0

#!/bin/bash

MATRIX="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"

LENGTH=$1

while [ "${n:=1}" -le "$LENGTH" ]

# ==> Recall that := is "default substitution" operator.

# ==> So, if 'n' has not been initialized, set it to 1.

PASS="$PASS${MATRIX:$(($RANDOM%${#MATRIX})):1}"

# ==> Very clever, but tricky.

# ==> Starting from the innermost nesting...

# ==> ${#MATRIX} returns length of array MATRIX.

# ==> $RANDOM%${#MATRIX} returns random number between 1

# ==> and [length of MATRIX] - 1.

# ==> ${MATRIX:$(($RANDOM%${#MATRIX})):1}

# ==> returns expansion of MATRIX at random position, by length 1.

# ==> See {var:pos:len} parameter substitution in Chapter 9.

# ==> and the associated examples.

# ==> PASS=... simply pastes this result onto previous PASS (concatenation).

# ==> To visualize this more clearly, uncomment the following line

# echo "$PASS"

# ==> to see PASS being built up,

# ==> one character at a time, each iteration of the loop.

let n+=1

# ==> Increment 'n' for next pass.

done

echo -n "$PASS" # ==> Or, redirect to a file, as desired.

exit 0

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Archive | Bash Scripting

Loop over lines in shell pipeline

Convert newlines to spaces

Get IP Address In A Script

maxclients.sh Script For Apache

getpass.sh Bash Script