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Full Discussion: Combining multiple greps
Top Forums UNIX for Beginners Questions & Answers Combining multiple greps Post 303031197 by RudiC on Saturday 23rd of February 2019 09:31:16 AM
Old 02-23-2019
In your post, you're not "grepping filenames", but grepping text that is the result of an ls command, containing file names.


As you pointed out, you need to differentiate between "grepping and globbing", which are not the same even though it sometimes may seem so. Either is a malapropism; the exact terms would be "regex matching" and "pattern matching".

"Globbing" deals with patterns and is done by the shell, mostly when dealing with directory contents. And, in one exceptional case, some recent shells can deal with regexes: in "conditional expressions". man bash:
Quote:
A ... binary operator, =~, is available ... the string to the right of the operator is considered an extended regular expression and matched accordingly
"Grepping" deals with regexes, basic and extended, abbr. BREs and EREs. They have many subtleties, and it pays off to spend some time reading the man page.

Patterns and regexes in principle have different syntaxes. There are some overlaps, e.g. the [...] bracket expression meaning "Match any one of the enclosed characters", but also "faux amis" (false friends) like the * . It's always annoying to keep those differences in mind when dealing with either, and I have to test and experiment every single time when I switch from one to the other.
Last edited by RudiC; 02-23-2019 at 11:45 AM..
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LEARN ABOUT MINIX

grep

GREP(1) 						      General Commands Manual							   GREP(1)

NAME

       grep - search a file for lines containing a given pattern

SYNOPSIS

       grep [-elnsv] pattern [file] ...

OPTIONS

       -e     -e pattern is the same as pattern

       -c     Print a count of lines matched

       -i     Ignore case

       -l     Print file names, no lines

       -n     Print line numbers

       -s     Status only, no printed output

       -v     Select lines that do not match

EXAMPLES

       grep mouse file	   # Find lines in file containing mouse

       grep [0-9] file	   # Print lines containing a digit

DESCRIPTION

       Grep  searches  one  or	more  files (by default, stdin) and selects out all the lines that match the pattern.  All the regular expressions
       accepted by ed and mined are allowed.  In addition, + can be used instead of * to mean 1 or more occurrences, ? can be used to mean 0 or  1
       occurrences,  and  |  can  be used between two regular expressions to mean either one of them.  Parentheses can be used for grouping.  If a
       match is found, exit status 0 is returned.  If no match is found, exit status 1 is returned.  If an error is detected,  exit  status  2	is
       returned.

SEE ALSO

       cgrep(1), fgrep(1), sed(1), awk(9).

																	   GREP(1)
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