topic Re: grep and replace text in a file in Operating System - Linux

grep and replace text in a file

MikeL_4 — Fri, 15 Feb 2008 14:02:17 GMT

I need a way to run a command in a script, that will grep for a parameter, and if fould, replace the entire line where it was found with a new line....

Any ideas on how to accomplish this ?

Thanks

Re: grep and replace text in a file

Tim Nelson — Fri, 15 Feb 2008 14:13:00 GMT

Either awk or sed is the way to go.
Give us and example and we will send some ideas.

Re: grep and replace text in a file

Elmar P. Kolkman — Fri, 15 Feb 2008 14:15:46 GMT

It will become something like:
awk '// { print "";next}{print}'

Re: grep and replace text in a file

James R. Ferguson — Fri, 15 Feb 2008 14:28:17 GMT

Hi:

How about?

# perl -pe 's/(.*trigger.*)/something new/' file

Thus, any line in the file containing the string "trigger" is totally replaced with a line that reads "something new".

Regards!

...JRF...

Re: grep and replace text in a file

MikeL_4 — Fri, 15 Feb 2008 19:21:52 GMT

I am checking for PASS_MAX_DAYS, and there are two occurances in the file, one being a comment line which I don't care about, only need to change the actual parameter line..

I've tried these two commands, but the end result is a blank file, which isn't good...

LIN=`/bin/grep -n "PASS_MAX_DAYS" /etc/login.defs | /bin/grep -v "#" | /bin/awk -F : '{print $1}'`
/bin/awk '{if (NR==${LIN}) $0="PASS_MAX_DAYS 30";print}' /etc/login.defs > /etc/login.defs.NEW

Re: grep and replace text in a file

MikeL_4 — Fri, 15 Feb 2008 19:32:28 GMT

A grep of the parameter shows two lines:

12:# PASS_MAX_DAYS Maximum number of days a password may be used.
17:PASS_MAX_DAYS 99999

whish is why I was trying to isolate the 2nd line for the actual line number that needs to be changed....

Thanks

Re: grep and replace text in a file

James R. Ferguson — Fri, 15 Feb 2008 19:54:11 GMT

Hi (again) Mike:

You could find the non-commented line matching the parameter you want and change the value that follows it like this:

# perl -pe 'next if /^\s*#/;s/(PASS_MAX_DAYS\s+)(\d+)\b(.*)/${1}1234${3}/' file

This would find lines (any or all) in your file that constain the string:

PASS_MAX_DAYS

...followed by whitespace (\s) and one or more digits (\d+) like:

PASS_MAX_DAYS 10

...or:

PASS_MAX_DAYS 10 #...change to your taste

...and in this example change the '10' to '1234'

If you want to perform this update in-place and retain a backup copy (*.old) of your file, do:

# perl -pi.old -e 'next if /^\s*#/;s/(PASS_MAX_DAYS\s+)(\d+)\b(.*)/${1}1234${3}/' file

Regards!

...JRF...

Re: grep and replace text in a file

MikeL_4 — Sat, 16 Feb 2008 01:03:36 GMT

ames, Thanks alot, the perl statement worked perfectly...