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Bash & sed question

Hi All!

I write a script that replace some lines following a pattern, using 'sed'.
The script works fine, but now i need to update it to replace only the last occurrence of that pattern en the file.
For example:

#a user
user= foo
name= John
password= 2312
#another user
user= tiger
name= Will
password= 5887

Im searching by the pattern '^user= '.

There is any way to replace ONLY the last occurrence of the pattern?

Thanks!

Hm, I'm sure that in any language You would have to loop through the occurences of ^user and save it in a list/array. Sed has that capability too. The last one received is the one You want to replace. But I couldn't help it, here's one in bash/sed that does the same thing. This is not a help with sed. But I think it illustrates what You want to do and the benefits of the *nix toolbox... I assume the file has a list of records where user is unique, and also that You separate the name with space before it, like:

lakris@ubuntu:~$ cat users.txt
#a user
user= foo
name= John
password= 2312
#another user
user= tiger
name= Will
password= 5887

lakris@ubuntu:~$ new=lion;org=`cat users.txt |grep ^user|tail -1|cut -d" " -f2`;cat users.txt|sed -e "s/^user=\ $org/user=\ $new/"
#a user
user= foo
name= John
password= 2312
#another user
user= lion
name= Will
password= 5887

lakris@ubuntu:~$

of course You could redirect it and do some file renaming and stuff to update the actual "database". lion could be Your input to a script, even the file name. Excercise left to reader...

Quote:

Originally Posted by rengo.Java

[...]
The script works fine, but now i need to update it to replace only the last occurrence of that pattern en the file.
For example:

#a user
user= foo
name= John
password= 2312
#another user
user= tiger
name= Will
password= 5887

Im searching by the pattern '^user= '.

There is any way to replace ONLY the last occurrence of the pattern?

Not a sed solution though:

Code:

ex - infile<<!

?^user=.*?s//your_new_entry/

x

!

in awk

Code:

awk 'FNR==NR{ if ($0 ~ /^user=/ ){

                n=NR                                

              }

              next

            }

      { 

        FNR==n ? $2="userlast": $2=$2

        print $0      

      }          

' "file"  "file"

output:

Code:

# ./test1.sh

#a user

user= foo

name= John

password= 2312

#another user

user= userlast

name= Will

password= 5887

Thanks to AL!!!
specially to lakris, your answer is clear and works ok!

Im a begginer in the bash world and there are several commands that i dont know (i.e: tail, cut, head) where can i found a list (or a reference) of that commands and what each do?

Again, THANKS TO ALL!!!!

PD: Sorry my gad english

Quote:

Originally Posted by rengo.Java

Well, *gad* isn't half bad ;)

I have found this, http://www.tldp.org/LDP/abs/html/ , to be a very good resource on bash (and the site http://www.tldp.org/ for most GNU/Linux tools). And of course, man tail, etc is a good way to start. Your distro may have additional documentation packages with HOWTO's and coding examples. A very good way to start is to look at how others solved a specific or similar problem.
I often find myself whipping up one-liners where others would turn to perl or even a higher level programming language. bash and friends are really powerful, fast and intuitive.
Happy hackin'!

/Lakris

I recently wrote a pretty complex name parser using cat, echo, cut, tr, rev, head, tail and grep.

Quote:

whipping up one-liners where others would turn to perl

Perl is quite happy to run a script given entirely on the commandline.

Code:

perl -e 'print "hello world\n";'

--- rod.

Quote:

Originally Posted by rengo.Java

somewhere down the road, as you progress in shell scripting, you will learn not to use cat for useless purposes such as :

Code:

cat file | grep "blah"

You will also learn how to get what you want without having to use too many pipes. have fun