The following script merges several files into one file.
#!/bin/bash
echo "Please specify a directory"
read folder
cd $folder
ls | sort -n
for i in *.fasta
do
cat $i >> virus
done
Line 5 creates a sorted list of directory contents. Line six loops through all files with .fasta extension. Line 8 appends contents of every file to the file virus.
Suppose I need to change the file extensions of certain files in a directory.
#!/bin/bash
echo "Please specify a directory: "
read folder
cd $folder
for i in *.txt
do
mv "$i" `basename $i txt`fasta
done
The directory address specified by the user is read into the script in line 2. This address is used to cd to the directory. This script changes the extensions of .txt files to .fasta.
For security reasons, most servers on the Internet do not show the contents of a directory if the directory address is typed. The user is either redirected to index.whatever, a default page, page not found or access denied. Thus the list of files in the directory are not displayed.
If you need to show the contents of your directory, you can use the following code:
If you want to list tables in MySQL, you simply type the following command:
show tables
Oracle does not provide such a short cut. You have to type the following command:
select * from user_objects where object_type = 'TABLE'
The word TABLE must be uppercase. This would lisl all tables in the database. The same query could be modified slightly to list functions, procedures, sequences, view and more.
List functions
select * from user_objects where object_type = 'TABLE'
List views
Extract function is used to extract year, month, or date from a date or timezone hour or timezone minute from an interval. Examples:
To change the first letter of the word to cap, use the inicap function. Use upper to covert to uppercase and lower to convert to lower case. Examples:
NVL2 function extends the funcitonality of NVL function. NVL function prints the value of the variable unless a null value is encountered; in which case a value is substituted for the null. In addition to this, NVL2 also allows you to substitute a value if the value of the variable is not null. Syntax:
NVL2(variable, not_null_substitute, null_substitute)
Example
Suppose you have two dates and you want to compares the years rather the exact date. Make sure you know the format of the dates. The use the following code:
to_char(to_date(somedate, 'yyyymmdd'), 'YYYY') = to_char(to_date(somedate, 'yyyymmdd'), 'YYYY')
Change yyyymmdd to your date format.
The substr function extracts a substring from a string. Syntax:
substr( string, start position, length)
where the first position is 1 and the length of the substring is optional. Some examples
This error occurs if a wrong value is passed when converting a number or string to date. To fix this problem, find out what date format the date is stored in e.g. yyyymmdd, dd-mm-yy, dd-mon-yy, etc. Then rewrite the to_date() statement with the correct format. For example