shell tips: get absolute path

$ cat abspath.sh
#!/bin/sh

echo $(cd $(dirname $0) && pwd)/$(basename $0)

shell script tips: bash and function

*** motivation ***
sh script does not have ${RANDOM} value which generates random value if used in bash script. Below is sample code explains how to use ${RANDOM} and define functions in bash scripts.

*** sample code (makeData.sh) ***

#!/bin/bash                                                                   

function create_db(){
  dbname=$1
  dbuser=$2
  dbpass=$3
  PGPASSWORD=${dbpass} dropdb -U ${dbuser} ${dbname}
  PGPASSWORD=${dbpass} createdb -U ${dbuser} ${dbname}
}

function create_tbl(){
  id=0
  dbname=$1
  dbuser=$2
  dbpass=$3
  dbtable=$4

  sql="CREATE TABLE ${dbtable} (id text, value int);"
  PGPASSWORD=${dbpass} psql -U ${dbuser} -d ${dbname} -c "${sql}"

  while [ ${id} -le 3 ]
  do
      id=`expr ${id} + 1`
      sql="INSERT INTO ${dbtable} VALUES (${id}, ${RANDOM});"
      PGPASSWORD=${dbpass} psql -U ${dbuser} -d ${dbname} -c "${sql}"
  done
}

function select_tbl(){
  dbname=$1
  dbuser=$2
  dbpass=$3
  dbtable=$4

  sql="SELECT * FROM ${dbtable};"
  PGPASSWORD=${dbpass} psql -U ${dbuser} -d ${dbname} -q -c "${sql}"
}

function main(){
  dbname=$1
  dbuser=$2
  dbpass=$3
  create_db ${dbname} ${dbuser} ${dbpass}

  sn=0
  prefix="table_"

  while [ ${sn} -le 23 ]
  do
      dbtable=${prefix}${sn}
      create_tbl ${dbname} ${dbuser} ${dbpass} ${dbtable}
      select_tbl ${dbname} ${dbuser} ${dbpass} ${dbtable}
      sn=`expr ${sn} + 1`
  done
}


# Program starts here!!!
if [ $# -ne 3 ]; then
  echo "usage: bash $0 dbname dbuser dbpass"
  exit
fi

main $1 $2 $3

*** output from above script ***

yaboo@maniac:~$ bash makeData.sh mydb test test 
id | value                                                                   
----+-------                                                                  
1  |   632                                                                   
2  |  5999                                                                   
3  |  3495                                                                   
4  |  3127                                                                   
(4 行)                                                                        
                                                                            
id | value                                                                   
----+-------                                                                  
1  | 29475                                                                   
2  |  7581                                                                   
3  | 17044                                                                   
4  | 12726                                                                   
(4 行)                                                                        
                                                                            
id | value                                                                   
----+-------                                                                  
1  | 13619                                                                   
2  | 25982                                                                   
3  | 21835                                                                   
4  | 23054                                                                   
(4 行)                                                                        
                                                                            
id | value                                                                   
----+-------                                                                  
1  |   726                                                                   
2  | 15405                                                                   
3  | 16549                                                                   
4  | 16405                                                                   
(4 行)                                                                        
                                                                            
id | value                                                                   
----+-------                                                                  
1  | 14362                                                                   
2  | 22030                                                                   
3  | 16364                                                                   
4  | 24379                                                                   
(4 行)                                                                        

...

id | value                                                                   
----+-------                                                                  
1  |  8468                                                                   
2  | 10413                                                                   
3  | 12345                                                                   
4  | 30637                                                                   
(4 行)                                                                        
                                                                            
id | value                                                                   
----+-------                                                                  
1  |  8372                                                                   
2  | 16466                                                                   
3  | 31683                                                                   
4  | 23073                                                                   
(4 行)                                                                        
                                                                            
yaboo@maniac:~$

postgres tips: How to Execute PostgreSQL Commands Inside Unix Shell Scripts

I've used to use -c option (method1) when execute postgreSQL command inside unix shell scripts. However, method1 supports single postgreSQL command and requires backslash '\' when postgreSQL is written by multiple lines. On the contrary, method2 supports multiple command at a time and does not require any backslash 8^). I think method2 is better than what I used to do(method1)

Method1: Using -c option

#!/bin/sh

dbname="mydb"
dbuser="postgres"
table1="test1"
table2="test2"

psql -U ${dbuser} -d ${dbname} -c "
DROP TABLE ${table1};"
psql -U ${dbuser} -d ${dbname} -c "
DROP TABLE ${table2};"
psql -U ${dbuser} -d ${dbname} -c "
CREATE TABLE ${table1} \
  (id int, \
  name text);"

psql -U ${dbuser} -d ${dbname} -c "
CREATE TABLE ${table2} \
  (id int, \
  name text);"

Method2: Using EOF operator

#!/bin/sh

dbname="mydb"
dbuser="postgres"
table1="test1"
table2="test2"

psql -d ${dbname} -U ${dbuser} << EOF
    DROP TABLE ${table1};
    DROP TABLE ${table2};
    CREATE TABLE ${table1}
      (id int,
      name text);
    CREATE TABLE ${table2}
      (id int,
      name text);
EOF

shell script tips: date command

"date" command is useful when we write a shell script which does per-day-processing.

#/bin/sh

fromdate="20110101"
todate="20110501"

date=${fromdate}
while [ ${date} -le ${todate} ]
do
  # do somewhat you want

  date=`date -d "$(date +2011-06-30) +1 day" +%Y%m%d`
done