Sort multiple files with bash

Question

I have a question that involves the bash scripting language.

I have multiple directories

• /studentName
• /studentMail
• /studentNumber

In each of these directories is a file name.txt, mail.txt, number.txt.

Now I need to create a function that will do the same as the SELECT function of a MySQL database. It doesn't need to read a single line. Just display all contents of those 3 files and sort them. which means i need something like this as output.

studentname | studentmail | studentnumber

I came up with 2 ways.

first:

cat /studentName/name.txt /studentMail/mail.txt /studentNumber/number.txt > summary
cat summary

This will display all contents of the 3 files under each other, which is obviously not good.

I also came up with this:

paste /studentName/name.txt /studentMail/mail.txt /studentNumber/number.txt

This does display all contents but still not really sorted. And I also later on need to be able to only select 1 row to be displayed.

Can anybody help me do this?

PS: I know about sort, but then all contents get displayed under each other, somehow I am not doing it right?

Answer 1

How are the files sorted now? Does line 3, say, of all three files refer to the same student? If so, you could expand your paste solution to this:

paste /studentName/name.txt /studentMail/mail.txt /studentNumber/number.txt | sort

which would sort all the records (lines) by student name. You could sort by some other field by using appropriate options to sort.

To select a single row to be displayed, follow whatever command yields a properly-sorted list with grep, e.g.,

paste ... | sort | grep 'pattern'

where 'pattern' would be your search criteria in the form of a regular expression. Of course, if you're selecting only one line, there is no need for sort.

Another command you might find useful is join, but I don't know enough about it to give you an example of its use.

Update: Formatting with awk

The output of the paste command above is a sequence of lines, each line consisting of three fields separated from each other by tabs, i.e.,

<field1><tab><field2><tab><field3>

These lines can be formatted by piping them into the following awk command.

awk -F '\t' '{printf "%-20s%-16s%s\n", $1, $2, $3}'

The -F '\t' argument specifies that the input field separator is a tab character. That will separate the input lines into three fields which awk refers to by $1, $2 and $3. The awk language includes a printf function that behaves essentially the same as the C library printf() function. The format string above specifies three string fields. The first, %-20s, specifies that the corresponding string parameter be left-justified in a 20-character field. The second, %-16s, specifies that its parameter be left-justified in a 16-character field. The last, %s, just appends its parameter to whatever has been formatted so far. Finally, the \n puts a newline at the end so that each input line is formatted to a separate output line.

To tune the output to your taste, just change the field widths and/or remove the minus signs to right-justify the strings. For more options, see the awk and printf man pages.

Answer 2

if you want to sort each file then paste the sorted data, with bash you can use process substitution:

paste -d '|' <(sort file1) <(sort file2) <(sort file3)