Most useful grep Options

-h:   suppress file names in output
-w:   restrict search to whole words only
-c:   displays count of matching lines in each file, not the lines themselves
      (note this is not the same as $ grep index *.rb | wc -l)
-i:   ignore case
-l:   list only file names containing matching lines
-n:   precede each line with the line number where it was found
-v:   display all lines NOT matching pattern
-C:   Display NUM lines of context either side of matches
-B:   Display NUM lines of context Before the matches
-A:   Display NUM lines of context After the matches

-e pattern: 
      Search for a pattern. Can use multiple times on a line
-r:   Search recursively from the current or specificed directory
  --include=pattern:
      Only search in file names matching pattern
  --exclude=pattern:
      Do not search in file names matching pattern

Most useful awk programs

awk '{ if (NF > max) max = NF }
     END { print max }'
    This program prints the maximum number of fields on any input line. 
awk 'length($0) > 80'
    This program prints every line longer than 80 characters. The sole rule has
    a relational expression as its pattern, and has no action (so the default
    action, printing the record, is used).
awk 'NF > 0'
    This program prints every line that has at least one field. This is an easy
    way to delete blank lines from a file (or rather, to create a new file
    similar to the old file but from which the blank lines have been deleted).
awk '{ if (NF > 0) print }'
    This program also prints every line that has at least one field. Here we
    allow the rule to match every line, then decide in the action whether to
    print.
awk 'BEGIN { for (i = 1; i <= 7; i++)
               print int(101 * rand()) }'
    This program prints 7 random numbers from 0 to 100, inclusive. 
ls -l files | awk '{ x += $4 } ; END { print "total bytes: " x }'
    This program prints the total number of bytes used by files. 
expand file | awk '{ if (x < length()) x = length() }
                  END { print "maximum line length is " x }'
    This program prints the maximum line length of file. The input is piped
    through the expand program to change tabs into spaces, so the widths
    compared are actually the right-margin columns.
awk 'BEGIN { FS = ":" }
     { print $1 | "sort" }' /etc/passwd
    This program prints a sorted list of the login names of all users. 
awk '{ nlines++ }
     END { print nlines }'
    This programs counts lines in a file. 
awk 'END { print NR }'
    This program also counts lines in a file, but lets awk do the work. 
awk '{ print NR, $0 }'
    This program adds line numbers to all its input files, similar to `cat -n'.
awk -F "\"*,\"*" '{print $3}' file.csv
    CSV parsing, prints 3rd field

This can helps you remember the unix cron syntax


# * * * * * command to be executed
# - - - - -
# | | | | |
# | | | | +- - - - day of week (0 - 6) (Sunday=0)
# | | | +- - - - - month (1 - 12)
# | | +- - - - - - day of month (1 - 31)
# | +- - - - - - - hour (0 - 23)
# +- - - - - - - - minute (0 - 59)

Allow oracle operating system user to schedule jobs on Linux / Unix

As the root user, add oracle to the /etc/cron.allow file with the echo command:

echo oracle >> /etc/cron.allow

Once the oracle entry is added to the /etc/cron.allow file, the os user oracle can use the crontab utility
to schedule a job

The root user can always schedule jobs with the crontab utility. Other users must be listed in
the /etc/cron.allow file. If the /etc/cron.allow file does not exist, then the operating system
user must not appear in the /etc/cron.deny file. If neither the /etc/cron.allow nor the /etc/
cron.deny file exists, then only the root user can access the crontab utility.

Usefull tips and command for the vi editor

This are the most used commands in vi edtor

Shell script to calculate Tablespaces sizes in Oracle

This shell take an ORACLE_SID as parameter and calculate in MB the sizes of tablespaces