issue with grep

soujanya_srk · #1 (**permalink**) 01-04-2008

using grep, i have a file emp.lst, and i want all those records
where "S" or "s" (capital or small) is not there

i used this

grep [^S] emp.lst

when i use grep [S] emp.lst

i am getting rows with S..but why negate (^) is not working?

theninja · #2 (**permalink**) 01-04-2008

I'm not exactly sure what you want out of the output, but try this

grep -vi s emp.lst

This will return everything without a S or s in the line.

joeyg · #3 (**permalink**) 01-04-2008

to get everything but, use the -v as previous post

the ^ is a special location character, similar to the $
the ^ locks to the beginning of text and the $ locks to end

sample.txt contains
begin this
more and more
then end

> grep "^begin" sample.txt
begin this
> grep "end$" sample.txt
then end

drl · #4 (**permalink**) 01-04-2008

Hi.

I think the invert, "-v", option is easiest to use. The "^", normally used as a beginning-of-line-anchor, takes on a special meaning when used in the character class notation, "[string_of_characters]", to mean "not these characters": "[^not_these]".

So you could use either method, the "-v", or the "[^]", but if you use a character class, you would need to set up the regular expression so that it would match every character on a line:

Code:

#!/usr/bin/env sh

# @(#) s1       Demonstrate expressions that match omitted characters.

set -o nounset
echo

debug=":"
debug="echo"

## The shebang using "env" line is designed for portability. For
#  higher security, use:
#
#  #!/bin/sh -

## Use local command version for the commands in this demonstration.

echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version bash

echo

FILE=${1-data1}
echo " Input file $FILE:"
cat $FILE

echo
echo " Results from grep:"
grep -vi "s" $FILE

echo
echo " Results from more complicated expression:"
grep '^[^sS]*$' $FILE

exit 0

Producing:

Code:

% ./s1

(Versions displayed with local utility "version")
GNU bash 2.05b.0

 Input file data1:
Line number one.
a
s
S
Line that shuld match character at end: s
S beginning on a line.
Line with s and S in the middle.
Line omitting the character for which we look.
Last line.

 Results from grep:
Line number one.
a
Line omitting the character for which we look.

 Results from more complicated expression:
Line number one.
a
Line omitting the character for which we look.

The use of regular expressions often takes lots of practice to use (and appreciate) ... cheers, drl

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