Rename the files in a directory by replacing a space with an underscore. The rename program comes with most modern Linux distros.

rename 's/\ /_/g' *.*

Put this export in .bashrc to make grep colorize the text it found.

export GREP_OPTIONS='--color=auto'

Sometimes you want to automate the running of a script or program, but the darn thing keeps asking questions and expects interactive answers. Shell scripting makes it easy to give the answers automatically, using a stream redirection from a file.

./qurious_program < predetermined_answers.txt

Useful when you want to append the contents of a whole file into something you are sed'ing. Be careful if you use -i, it will replace the working file.

sed -i "/attr_accessor :config/r ../patch_for_application.rb.tmpl" app/controllers/application.rb

This script tests if nginx exists and is executable. The script prints a warning and exits, if nginx doesn't exists or isn't executable:

DAEMON=/usr/local/sbin/nbinx
if [ ! -x $DAEMON ]
then
   echo "Couldn't find $DAEMON. Please set path to DAEMON."
   exit 0
fi

See man test for more information on how to use the test command.

Use this to convert WMA files to MP3 in Linux.

#!/bin/bash
# By Marko Haapala
# converts wma to mp3 recursively. does not delete any static files, so 
# cleanup and renaming is needed afterwards. 
#
# requirements:
# lame    - http://lame.sourceforge.net/download.php
# mplayer - apt-get install mplayer or http://www.mplayerhq.hu/design7/dload.html


current_directory=$(pwd)
wma_files=$(find "${current_directory}" -type f -iname "*.wma")
# Need to change IFS or files with filenames containing spaces will not
# be handled correctly by for loop
IFS=$'\n' 
for wma_file in ${wma_files}; do 
    mplayer -vo null -vc dummy -af resample=44100 \
    -ao pcm -ao pcm:waveheader "${wma_file}" && lame -m s \
    audiodump.wav -o "${wma_file}".mp3
    rm audiodump.wav
done

Remove id3 tags from MP3 files recursively.

#!/bin/bash
# By Marko Haapala
# requirements:
# id3ed - apt-get install id3ed
IFS=$'\n'
for mp3_file in $(find ./ -type f -iname '*.mp3'); do
    id3ed -r "${mp3_file}"
done

Use find instead of rm:

find . -name '*' | xargs rm

The command deletes all files in the current directory.

Expect can come in handy when you can't configure ssh public key authentication on the servers :) (and the system "architect" hasn't yet realized the wonderfulness of a log host).

#!/bin/bash
#
# Usage: script <username> <password> <build>
#
# Example ./copy_logs_from_production.sh marko hubbabubba current
#

username=$1
password=$2
build=$3
mkdir $build

instance_1_server=10.0.0.1
instance_2_server=10.0.0.1
instance_3_server=10.0.0.2
instance_4_server=10.0.0.2
instance_5_server=10.0.0.3
instance_6_server=10.0.0.3
instance_7_server=10.0.0.4
instance_8_server=10.0.0.4
instance_9_server=10.0.0.5

servers=("$instance_1_server" "$instance_2_server" "$instance_3_server" "$instance_4_server" "$instance_5_server" "$instance_6_server" "$instance_7_server" "$instance_8_server" "$instance_9_server" )
i=1
for server in ${servers[@]}; do
  expect -c "
            # exp_internal 1 # uncomment for debugging
            spawn /usr/bin/scp $username@$server:/var/logs/application/$build/server${i}/error.log $build/error-${i}.log
            expect { 
              "*password:*" { send $password\r\n; interact } 
              eof { exit }
            }
            exit
            "
  let "i=i+1"
done

To append to a stream in bash without the trailing line feed use printf to format the output before appending it to the stream.

i=42
FILE=/tmp/atm
printf "%s" "${i}" > $FILE