Shell script: format numbers

Shell script to format date in yyyy.mm.dd format

#!/bin/bash

year=2012

for (( c=1; c<=12; c++ ))
do
   month=$(printf "%02d" $c)

  for (( d=1; d<=15; d++ ))
  do
     day=$(printf "%02d" $d)
     echo $year.$month.$day
  done
done

Bash: read csv file

Here is the script to read csv file in shell script.

#!/bin/bash
FILENAME=test.csv
OLDSEP=$IFS
IFS=,

[ ! -f $FILENAME ] && { echo "File not found : $FILENAME"; exit 99; }

while read field1 field2 field3 field4
do
    echo "$field1 : $field2 : $field3 : $field4"
done < $FILENAME

IFS=$OLDSEP

Shell Script: Find number of elements in an array

shell (bash) provides one-dimensional array variables. Any variable may be used as an array and there is no maximum limit on the size of an array. Below is the way to find length of array in shell script.

#!/bin/bash
SERVERS=(SERVER1 SERVER2 SERVER3 SERVER4)
# set length of an array
arrayLength=${#SERVERS[*]}
# or
#arrayLength=${#SERVERS[@]}

#Traverse each entry
for (( i=0; i<${arrayLength}; i++ ));
do
  echo ${SERVERS[$i]}
done

Find the day diff between two days

Following is the shell script solution for getting number of days between two dates:

#/bin/sh
date1=`date +%s -d $1`
date2=`date +%s -d $2`
diff=`expr $date2 - $date1`
diff_days=`expr $diff / \( 60 '*' 60 '*' 24 \)`
echo $diff_days


[vishnu@ shell]# ./daydiff.sh 2010-08-02 2010-09-15
44
[vishnu@ shell]#

Here is the perl solution for the same:

#!/bin/perl
use strict;
use warnings;
use Time::Local;

my $date1 = $ARGV[0];
my $date2 = $ARGV[1];

my @formatted_date1 = split(/-/, $date1);
my @formatted_date2 = split(/-/, $date2);

my $local_date1 = timelocal(0, 0, 0, $formatted_date1[2], $formatted_date1[1], $formatted_date1[0]);
my $local_date2 = timelocal(0, 0, 0, $formatted_date2[2], $formatted_date2[1], $formatted_date2[0]);

my $diffSeconds = $local_date2- $local_date1;
my $diffDays = $diffSeconds / (60 * 60 * 24);
print "Day diff :: $diffDays\n";

[vishnu@ shell]# ./daydiff.pl 2010-08-02 2010-09-15
Day diff :: 43
[vishnu@ shell]#

Here is modified version of above shell script, if you want to find out time difference in seconds

#!/bin/bash

d1=`date +%s -d "$1"`
d2=`date +%s -d "$2"`
((diff_sec=d2-d1))
echo "Diff Seconds : $diff_sec"

[vishnu@ shell]#./date.sh "2011-07-19 22:44:34" "2011-07-20 02:04:14"
Diff Seconds : 11980
[vishnu@ shell]#

Dump cpu and memory usage of a process

Here is the automated shell script which can dump the memory and cpu usage of a process. Helpful in cases when you want to monitor a process for a long time.

#!/bin/bash

if [ "$#" -ne 1 ]; then
echo "Usage ... [$0 <pid>]"
exit
fi

pid=$1

# maxRunTime is used to control the script, so that it run only for specified number of seconds
maxRunTime=72000
# sleepTime is used to sleep for specified seconds, to take the memory dump again
sleepTime=120

logFile=${pid}_process.log
commandFile=${pid}_command.log

`ptree $pid >> $commandFile`;
`pargs $pid >> $commandFile`;

currentRunTime=0

while [ $currentRunTime -lt $maxRunTime ]
do
time=`date +%F::%X | tr -d '[\n]'`
line=`ps -eo pid,pcpu,vsz | grep $pid`;
echo "$time $line" >> $logFile
sleep $sleepTime
currentRunTime=`expr $currentRunTime + $sleepTime`
echo "Execution Time : ${currentRunTime} seconds [max ${maxRunTime}]"
done;

Using variable with sed inside a shell script

For using sed inside a shell script, The variable should be in "double quotes" and the command in 'single quotes'. Following is the example

#!/bin/bash

usage () {
echo "$0 -s < name> -r <replace name> -f <file name>"
exit
}

while getopts s:r:f: option
do
case "$option" in
s) search="$OPTARG";;
r) replace="$OPTARG";;
f) filename="$OPTARG";;
\?) usage
esac
done

sed -i 's/'"$search"'/'"$replace"'/g' "$filename"

Special Shell Script Variables

There are some variables which are set internally by the shell and which are available to the user:

$1 - $9   These variables are the positional parameters.

$0        The name of the command currently being executed.

$#        The number of positional arguments given to this invocation of the shell.

$?        The exit status of the last command executed is given as a decimal string.
       When a command completes successfully, it returns the exit status of 0
       (zero), otherwise it returns a non-zero exit status.

$$        The process number of this shell - useful for including in filenames, to
       make them unique.

$!        The process id of the last command run in the background.

$-        The current options supplied to this invocation of the shell.

$*        A string containing all the arguments to the shell, starting at $1.

$@@       Same as above, except when quoted.