Tag: bash

Replace an old IP with new one in all files of all sub-directories recursively

Here is a quick Linux tip for those who want to replace their old IP with new one for all files in a given directory and all its sub-directories recursively:

find [path-to-directory] -type f -print0 | xargs -0 sed -i 's[old-IP-escape-dot]/[new-IP]/g'

Quick example:

find /etc/nginx/ -type f -print0 | xargs -0 sed -i 's/192\.168\.10\.124/10.10.10.224/g'

As you can see the directory is “/etc/nginx” and replace it with the directory where are your (configuration) files are. We are replacing old IP=192.168.10.124 with the new one 10.10.10.224, so after the execution of the above line you’ll get modified files with IP 10.10.10.224.
You must escape the dot “.” in the IP!

Busybox ash, Debian dash and simulating bash arrays

Busybox ash (Almquist shell) shell and Debian dash (Debian Almquist shell) are lightweight Unix shell and they are a variant of System V.4 variant of the Bourne shell. Ash/dash shell is known to be very small and is used mainly in embedded (ash) devices and installation scripts (Debian/Ubuntu setup).
Unfortunately they do not support arrays, which could be really a problem in many cases. But we can simulate the arrays with eval function.
So if you need to write a ash/dash script let’s say for an installation script of Ubuntu or Debian or a script for an embedded device, which uses busybox or even you do not want to use arrays in bash, you can follow the consepts below – create variable with a “name” concatenated with a number.

  • 1) Set a variable

    It can be done with two ways:

    1. for myi in 0 1 2 ; do
    setvar mvar$myi "Payload: $myi"
done

    2. for myi in 0 1 2 ; do
    eval mvar$myi=\"Payload: $myi\"
done

    This will create variables with names:

    mvar1, mvar2, mvar3

    and they can be used in any place of your script after the creation of the variables using “eval” or accessing them with the names.

    * bash shell do not support the command “setvar”, so for bash scripts use only eval version.

  • 2) Use a variable

    1. using “eval” 
      for myi in 0 1 2 ; do
    eval echo \$mvar$myi
done

myi=1
eval newvar="\$mvar$myi"
echo $newvar
    2. direct access 
      echo $mvar2
$mvar2="Payload 20"
echo $mvar2

bash: find all files between a given time period

Here is the command to find all files between two given dates with find linux command:

find /home/ -newermt 20140901T0000 -not -newermt 20141001T0000 -type f

to use “find” with

-newermt

you must have find version above 4.3.3.
With older version of the find utility it can be used with the time of two files.

  1. create two temporary files
  2. “touch” them with the right time
  3. execute find command with “-newer”
  4. delete the two temporary files

Here is the bash code:

dt1=$(date -d '2014-09-01' +'%Y%m%d%H%M.%S'); dt2=$(date -d '2014-10-01' +'%Y%m%d%H%M.%S'); touch -t $dt1 "$dt1"; touch -t $dt2 "$dt2"; find . -type f -newer "$dt2" -not -newer "$dt1";rm "$dt1" "$dt2"