How to grep string in a fixed position?

[praise12]

Hey there
How to use grep to search for a pattern/string in a fixed length file eg.in position 10-20 or field 3 only?
Thanks for your help in advance!

 

[misercord]

For a fix colum this works
grep &quot;..........<string>&quot; file

 

[praise12]

grep &quot; string&quot; <file> will return all the rows which containing the search string found. But, what I need is able to pull out the string/pattern from certain position, such as field 3 or position 1 to 20, can I use grep here? and if yes, how to identify the position or field in the same 'grep' command?

 

[aigles]

Hi,

With grep you cannot specify the positions where to search for the pattern.

A solution is to use awk.
Look at this little example:

--- xgrep ---
if [ $# -lt 3 ] ; then
echo &quot;Usage: $0 pattern start end [file...]&quot; 2>&1
exit 1
fi
Pattern=&quot;$1&quot;
Start=$2
End=$3
let Len=End-Start+1
shift 3
awk -v START=$Start -v LEN=$Len -v PATTERN=$Pattern '
substr($0,START,LEN) ~ PATTERN ' $*
-- End of xgrep ---

For example, to search the pattern &quot;M[01][0-9]&quot; in position 10-12 of file :

xgrep &quot;M[01][0-9]&quot; 10 12 inputfile

Jean Pierre.

 

[MikeLacey]

If would have thought that misercord's example above would work fine. To find lines in file.txt where the string 'help' starts in the 8 character I would type:

grep '.......help' file.txt

I don't have a UNIX system here at the moment (reinstalling HPUX as I type) so I can't test it, sorry. Mike
&quot;Experience is the comb that Nature gives us after we are bald.&quot;

Is that a haiku?
I never could get the hang
of writing those things.