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Full Discussion: Pattern matching question
Top Forums Shell Programming and Scripting Pattern matching question Post 302387451 by HobieCoop on Friday 15th of January 2010 10:25:23 PM
Old 01-15-2010
egrep ^"[^0-9]+${PNUM}[^0-9]" /bb/data/firmexbytes.dta

First - ${PNUM} is just a variable that contains a string - any string.

So now, let's break down the egrep command chunk by chunk...

egrep ^
This means start looking for the pattern at the start of each line

egrep ^"[^0-9]+
The ^ inside the bracket before a pattern means NOT. 0-9 mean any digit 0 thru 9. So [^0-9] means look for any single character that is not a digit 0 thru 9. The + means match 1 or more instance of the preceding expression. So ^"[^0-9]+ means look for 1 or more characters in a row that are not digits 0 thru 9 starting at the beginning of each line.

egrep ^"[^0-9]+${PNUM}
${PNUM} is just a variable that contains a string - any string. So ^"[^0-9]+${PNUM} means look for the string ${PNUM} and return the line as long as there are no numbers preceding the string ${PNUM}.

egrep ^"[^0-9]+${PNUM}[^0-9]"
Finally we end with [^0-9] which says look for any single character that is not a digit 0 thru 9. And since there is no + after it, it says to only look at the next character after ${PNUM} is found. And it MUST find at least one non-numeric character.


For the sake of this discussion let's say that:

PNUM=junk

So - the egrep statement will scan the /bb/data/firmexbytes.dta file and return any lines that have the string "junk" in it with 1 or more characters before the string with none of them a number AND a character that exists immediately after "junk" that is not a number.

Here's another example:

PNUM=1234

In this case - the egrep statement will scan the /bb/data/firmexbytes.dta file and return any lines that have the string "1234" in it with 1 or more characters before the string with that are not a number AND a character that exists immediately after "1234" that is not a number.


Want to have fun? Put the following in a file called file1:

Code:
junk
ajunk
0junk
ajunk0
ajunka
abcjunkz
abcjunkxyz
abcjunkx12
a0cjunka
junka
junk0

Then run

Code:
PNUM=junk
egrep ^"[^0-9]+${PNUM}[^0-9]" file1

Of all those values found in the list above, egrep will only return these:
ajunka
abcjunkz
abcjunkxyz
abcjunkx12
because they are the only ones that have the string "junk" in it with 1 or more characters before the string with none of them a number AND a character that exists immediately after "junk" that is not a number.

abcjunkx12 should not be a surprise ...

Now change junk to 1234 both in the file and as the value of PNUM and try the egrep again.

Got it??? Should be clear as mud at this point....
 

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LEARN ABOUT OPENSOLARIS

egrep

egrep(1)							   User Commands							  egrep(1)

NAME

       egrep - search a file for a pattern using full regular expressions

SYNOPSIS

       /usr/bin/egrep [-bchilnsv] -e pattern_list [file...]

       /usr/bin/egrep [-bchilnsv] -f file [file...]

       /usr/bin/egrep [-bchilnsv] pattern [file...]

       /usr/xpg4/bin/egrep [-bchilnqsvx] -e pattern_list [-f file]
	    [file...]

       /usr/xpg4/bin/egrep [-bchilnqsvx] [-e pattern_list] -f file
	    [file...]

       /usr/xpg4/bin/egrep [-bchilnqsvx] pattern [file...]

DESCRIPTION

       The  egrep  (expression grep) utility searches files for a pattern of characters and prints all lines that contain that pattern. egrep uses
       full regular expressions (expressions that have string values that use the full set of alphanumeric and special characters)  to	match  the
       patterns. It uses a fast deterministic algorithm that sometimes needs exponential space.

       If  no  files  are  specified,  egrep  assumes standard input. Normally, each line found is copied to the standard output. The file name is
       printed before each line found if there is more than one input file.

   /usr/bin/egrep
       The /usr/bin/egrep utility accepts full regular expressions as described on the regexp(5) manual page, except for ( and ), ( and ),	{
       and }, < and >, and 
, and with the addition of:

	   1.	  A full regular expression followed by + that matches one or more occurrences of the full regular expression.

	   2.	  A full regular expression followed by ? that matches 0 or 1 occurrences of the full regular expression.

	   3.	  Full regular expressions separated by | or by a NEWLINE that match strings that are matched by any of the expressions.

	   4.	  A full regular expression that can be enclosed in parentheses ()for grouping.

       Be careful using the characters $, *, [, ^, |, (, ), and  in full regular expression, because they are also meaningful to the shell. It is
       safest to enclose the entire full regular expression in single quotes (a'a').

       The order of precedence of operators is [], then *?+, then concatenation, then | and NEWLINE.

   /usr/xpg4/bin/egrep
       The /usr/xpg4/bin/egrep utility uses the regular expressions described in the EXTENDED REGULAR EXPRESSIONS section of the  regex(5)  manual
       page.

OPTIONS

       The following options are supported for both /usr/bin/egrep and /usr/xpg4/bin/egrep:

       -b		  Precede  each  line  by  the block number on which it was found. This can be useful in locating block numbers by context
			  (first block is 0).

       -c		  Print only a count of the lines that contain the pattern.

       -e pattern_list	  Search for a pattern_list (full regular expression that begins with a -).

       -f file		  Take the list of full regular expressions from file.

       -h		  Suppress printing of filenames when searching multiple files.

       -i		  Ignore upper/lower case distinction during comparisons.

       -l		  Print the names of files with matching lines once, separated by NEWLINEs. Does not repeat the names of  files  when  the
			  pattern is found more than once.

       -n		  Precede each line by its line number in the file (first line is 1).

       -s		  Work silently, that is, display nothing except error messages. This is useful for checking the error status.

       -v		  Print all lines except those that contain the pattern.

   /usr/xpg4/bin/egrep
       The following options are supported for /usr/xpg4/bin/egrep only:

       -q    Quiet.  Does  not	write  anything  to  the standard output, regardless of matching lines. Exits with zero status if an input line is
	     selected.

       -x    Consider only input lines that use all characters in the line to match an entire fixed string or regular expression  to  be  matching
	     lines.

OPERANDS

       The following operands are supported:

       file    A path name of a file to be searched for the patterns. If no file operands are specified, the standard input is used.

   /usr/bin/egrep
       pattern	  Specify a pattern to be used during the search for input.

   /usr/xpg4/bin/egrep
       pattern	  Specify  one	or more patterns to be used during the search for input. This operand is treated as if it were specified as -epat-
		  tern_list..

USAGE

       See largefile(5) for the description of the behavior of egrep when encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).

ENVIRONMENT VARIABLES

       See environ(5) for descriptions of the following environment variables that affect the execution of egrep:  LC_COLLATE,	LC_CTYPE,  LC_MES-
       SAGES, and NLSPATH.

EXIT STATUS

       The following exit values are returned:

       0    If any matches are found.

       1    If no matches are found.

       2    For syntax errors or inaccessible files (even if matches were found).

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

   /usr/bin/egrep
       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+
       |CSI			     |Not Enabled		   |
       +-----------------------------+-----------------------------+

   /usr/xpg4/bin/egrep
       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWxcu4			   |
       +-----------------------------+-----------------------------+
       |CSI			     |Enabled			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       fgrep(1), grep(1), sed(1), sh(1), attributes(5), environ(5), largefile(5), regex(5), regexp(5), XPG4(5)

NOTES

       Ideally there should be only one grep command, but there is not a single algorithm that spans a wide enough range of space-time trade-offs.

       Lines are limited only by the size of the available virtual memory.

   /usr/xpg4/bin/egrep
       The /usr/xpg4/bin/egrep utility is identical to /usr/xpg4/bin/grep -E. See grep(1). Portable applications should use /usr/xpg4/bin/grep -E.

SunOS 5.11							    24 Mar 2006 							  egrep(1)
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