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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 CENTOS

zipgrep

ZIPGREP(1L)															       ZIPGREP(1L)

NAME

       zipgrep - search files in a ZIP archive for lines matching a pattern

SYNOPSIS

       zipgrep [egrep_options] pattern file[.zip] [file(s) ...]  [-x xfile(s) ...]

DESCRIPTION

       zipgrep	will  search  files  within  a ZIP archive for lines matching the given string or pattern.  zipgrep is a shell script and requires
       egrep(1) and unzip(1L) to function.  Its output is identical to that of egrep(1).

ARGUMENTS

       pattern
	      The pattern to be located within a ZIP archive.  Any string or regular expression accepted by egrep(1) may be used.  file[.zip] Path
	      of  the  ZIP archive.  (Wildcard expressions for the ZIP archive name are not supported.)  If the literal filename is not found, the
	      suffix .zip is appended.	Note that self-extracting ZIP files are supported, as with any other ZIP archive; just	specify  the  .exe
	      suffix (if any) explicitly.

       [file(s)]
	      An  optional list of archive members to be processed, separated by spaces.  If no member files are specified, all members of the ZIP
	      archive are searched.  Regular expressions (wildcards) may be used to match multiple members:

	      *      matches a sequence of 0 or more characters

	      ?      matches exactly 1 character

	      [...]  matches any single character found inside the brackets; ranges are specified by a beginning character, a hyphen, and an  end-
		     ing character.  If an exclamation point or a caret (`!' or `^') follows the left bracket, then the range of characters within
		     the brackets is complemented (that is, anything except the characters inside the brackets is considered a match).

	      (Be sure to quote any character that might otherwise be interpreted or modified by the operating system.)

       [-x xfile(s)]
	      An optional list of archive members to be excluded from processing.  Since wildcard characters  match  directory	separators  (`/'),
	      this  option  may  be used to exclude any files that are in subdirectories.  For example, ``zipgrep grumpy foo *.[ch] -x */*'' would
	      search for the string ``grumpy'' in all C source files in the main directory of the ``foo'' archive, but none in any subdirectories.
	      Without the -x option, all C source files in all directories within the zipfile would be searched.

OPTIONS

       All options prior to the ZIP archive filename are passed to egrep(1).

SEE ALSO

       egrep(1), unzip(1L), zip(1L), funzip(1L), zipcloak(1L), zipinfo(1L), zipnote(1L), zipsplit(1L)

URL

       The Info-ZIP home page is currently at
       http://www.info-zip.org/pub/infozip/
       or
       ftp://ftp.info-zip.org/pub/infozip/ .

AUTHORS

       zipgrep was written by Jean-loup Gailly.

Info-ZIP							   20 April 2009						       ZIPGREP(1L)
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