Problems with "grep -vf", and exclusion files


 
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Old 12-01-2013
Quote:
Originally Posted by Doug Lassiter
A blank "out" file is quickly created, but the command line doesn't report that it the command has finished. It just hangs. I am careful, by the way, not to have blank lines in my "exclude" file. top tells me that the grep process is still working hard (100% of CPU!), but the "out" file remains blank. That's what I call "never-never land".
The output file is not "blank" -- it's a zero length file. Any time you use the redirection operator > in a command line it will immediately truncate the file to zero regardless of file size. This happens before grep gets executes.

I am not sure why the CPU is pegged with your test case but I wanted to clarify that behaviour.
 
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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)