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Full Discussion: regular expressions memory
Top Forums UNIX for Advanced & Expert Users regular expressions memory Post 302337807 by wakatana on Saturday 25th of July 2009 11:37:48 AM
Old 07-25-2009
regular expressions memory
Hi all, i have read in one site (i can put link, but is in Czech language ) that regular expressions have some kind of memory. If i understood it propertly when i want to remebmer some part of regexp i just put it between \( and ) and then call it by \1 \2 \3 etc. where \$number is number of memored expression. So i tried some examples bud didnt work for me :

lets say i want to know only UID and HOME from /etc/passwd so i tried followings:

Code:
grep -E "^[^:]*:[^:]*:\([^:]*):[^:]*:[^:]*:\([^:]*):[^:]*" /etc/passwd
grep -E "^[^:]*:[^:]*:\([^:])*:[^:]*:[^:]*:\([^:])*:[^:]*" /etc/passwd

but neither one works. I know i didnt call \1 and \2 but i dont know how.

also tried append "end" string to end of all lines of file

Code:
sed -e 's/\(.*)/\1end/' file_name

with the same result as prevouis.

I know both tasks can be done using some other utils such as sed. But just for curiosity i want know more about regexp memory. Thanks a lot

---------- Post updated at 05:37 PM ---------- Previous update was at 05:32 PM ----------

Noticed that the block of text that to be memored must be in \(....\), works in sed, in grep still dont know how to print just \1 \2
 

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LEARN ABOUT MINIX

zgrep

ZGREP(1)                                                      General Commands Manual                                                     ZGREP(1)

NAME

       zgrep - search possibly compressed files for a regular expression

SYNOPSIS

       zgrep [ grep_options ] [ -e ] pattern filename...

DESCRIPTION

       Zgrep  invokes  grep  on  compressed  or  gzipped  files.   These  grep  options  will  cause  zgrep  to  terminate  with  an  error  code:
       (-[drRzZ]|--di*|--exc*|--inc*|--rec*|--nu*).  All other options specified are passed directly to grep.  If no file is specified,  then  the
       standard input is decompressed if necessary and fed to grep.  Otherwise the given files are uncompressed if necessary and fed to grep.

       If the GREP environment variable is set, zgrep uses it as the grep program to be invoked.

EXIT CODE

       2 - An option that is not supported was specified.

AUTHOR

       Charles Levert (charles@comm.polymtl.ca)

SEE ALSO

       grep(1), gzexe(1), gzip(1), zdiff(1), zforce(1), zmore(1), znew(1)

                                                                                                                                          ZGREP(1)
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