Linux sorting, crontab & concat

October 15, 2014 · by · in Linux

Linux: Sorting a File

Here’s simple ‘sort’ command that will remove the duplicate entry from any file and sort in ascending order:Consider a file with few numbers:

[root@myhost tmp]# cat testSort.txt
23
4
56
001
34
3

To sort it:

[root@myhost tmp]# sort -u testSort.txt > sortd_testSort.txt

wherein, -u –> Unique

Its sorted:

[root@myhost tmp]# cat sortd_testSort.txt
001
23
3
34
4
56
Oops! Though it worked, it didn’t work correctly. Because the file contains numeric data.

So use the below:

[root@myhost tmp]# sort -u -n testSort.txt > numeric_sortd_testSort.txt wherein, -n –> for numeric data

And, now its correct:

[root@myhost tmp]# cat numeric_sortd_testSort.txt
001
3
4
23
34
56

However, this works only for the small files. Smaller than space available with ‘/tmp’ partition.

If you want to sort huge files, use the below:

[root@myhost lib]# sort -u -n -T. testSort.txt > numeric_sortd_testSort_new.txt wherein, -T. –> T indicates the location used as temporary space. By default its ‘/tmp’.

‘.’ indicates current directory

Linux: Crontab – Brief

I always get confuse whenever I want to set a new cron job. The confuse is with regard to the options too be set!
For those who new to ‘cron’, its nothing but, an event scheduler in Linux. That means, you can schedule any script to run at any time you wanted to. Its just the system/server should be up and running!cron job is specific to every user in Linux/Unix. So, one can’t see other’s cron unless the necessary privileges or sudo root access given.

Whatever, here is the options in cron:

To check cron jobs:

[root@localhost kiran]# crontab -l
no crontab for root

To set cron jobs:
[root@localhost kiran]# crontab -e
After adding, here is how it looks:
[root@localhost kiran]# crontab -l
##Script to test
00 */2 1-31 * 0,2,3   sh /home/kiran/test.sh >> /dev/null

Every Cron job should be given with 5 options:

  • minute -> 0-59
  • hour -> 0-23
  • day of month -> 1-31
  • month -> 1-12
  • day of week -> 0-7 (0 is Sunday )
In the above example:
00 — 0th Minute
*/2 — Every 2 hours
1-31 — Every day (1 to 31)
* — Every Month
0,2,3 — Sunday,Tuesday,Wednesday

Linux: Concatenate In Linux

Here is the commands to concatenate in Linux.

Consider a file as below:

[root@myserver 6048]# cat test.txt
12
0
123445456
234565443
3883
33

My requirement is to generate update/delete statement for each of this value. Think of a file with millions of records.

My update statement would be:

update mytable set col1=’Yes’ where col2=’ value in the file‘;

Here’s the solution:

[root@myserver 6048]# cat test.txt | sed “s/^/update mytable set col1=’Yes’ where col2=’/g;s/$/’;/g”
update mytable set col1=’Yes’ where col2=’12’;
update mytable set col1=’Yes’ where col2=’0′;
update mytable set col1=’Yes’ where col2=’123445456′;
update mytable set col1=’Yes’ where col2=’234565443′;
update mytable set col1=’Yes’ where col2=’3883′;
update mytable set col1=’Yes’ where col2=’33’;
update mytable set col1=’Yes’ where col2=”;
update mytable set col1=’Yes’ where col2=’987676′;

You may redirect the output to some other file, as below:

[root@myserver 6048]# cat test.txt | sed “s/^/update mytable set col1=’Yes’ where col2=’/g;s/$/’;/g” > updates_test.sql

You may also use the below query for the purpose:

[root@myserver 6048]# sed  “s/^/update mytable set col1=’Yes’ where col2=’/g;s/$/’;/g”  test.txt > updates_test.sql

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