Replace 2nd to last Character with SED

elproducto · 03-30-2009, 05:44 PM

I have a quick question. I use a command that pulls computer name and would like to use SED to change the second to last character from W to M. An example of command output would be MACIMAW1 and I would like to change the second to last character to M so in this case MACIMAW1 would change to MACIMAM1. For this is used networksetup -getcomputername |sed s/W/M/, This work fine until I get a result with multiple W's for example WWHILW1, in that case my SED string would return MWILW1. Any help would be greatly appreciated. Thanks

kenoshi · 03-30-2009, 06:40 PM

Quote:

Originally Posted by elproducto

I have a quick question. I use a command that pulls computer name and would like to use SED to change the second to last character from W to M. An example of command output would be MACIMAW1 and I would like to change the second to last character to M so in this case MACIMAW1 would change to MACIMAM1. For this is used networksetup -getcomputername |sed s/W/M/, This work fine until I get a result with multiple W's for example WWHILW1, in that case my SED string would return MWILW1. Any help would be greatly appreciated. Thanks

You can try something like:

Code:

networksetup -getcomputername | sed -re 's/W([0-9a-zA-Z])$/M\1/'

There's probably better ways to do this, but hope this helps.

syg00 · 03-30-2009, 06:46 PM

sed -r 's/(.*)W(.)$/\1M\2/' should probably do it

<Edit:> thanks to kenoshi, why don't I simplify it to ... sed -r 's/W(.)$/M\1/'

ghostdog74 · 03-30-2009, 07:35 PM

awk

Code:

# echo MACIMAW1 | awk 'BEGIN{OFS=FS=""}{$(NF-1)="M"}1'
MACIMAM1

elproducto · 03-31-2009, 12:35 PM

Thanks Guys for all the help.

For some reason the Mac OS version of sed does not like -r option and none of the Sed command worked for me I got error

Code:

sed: illegal option -- r
usage: sed script [-Ealn] [-i extension] [file ...]
       sed [-Ealn] [-i extension] [-e script] ... [-f script_file] ... [file ...]

When I take out the -r, I get the following error

Code:

sed: 1: "s/W(.)$/M\1/": \1 not defined in the RE

The AWK Script works perfectly on Mac OS and also add the M1 to computer that do not have the W in the second position. Thanks again for the help

Telemachos · 03-31-2009, 12:41 PM

Quote:

Originally Posted by elproducto

Thanks Guys for all the help.

For some reason the Mac OS version of sed does not like -r option and none of the Sed command worked for me I got error

Code:

sed: illegal option -- r
usage: sed script [-Ealn] [-i extension] [file ...]
       sed [-Ealn] [-i extension] [-e script] ... [-f script_file] ... [file ...]

On OS X, you get the BSD version of sed rather than GNU sed, which is what most Linux distros have. The BSD version doesn't support all the options of the GNU version, and they can differ in subtle and annoying ways. (One of the great joys of the history of Unix and Linux is different implementations of core utilities.) If you want to get the GNU version, check out MacPorts or Fink.

And, just for fun, here's a Perl version:

Code:

echo MACIMAW1 | perl -pe 'substr($_, -3, 1, 'M')' -

(If it bothers you that the offset is -3 (three characters back starting at the end of the string), remember that Perl counts back starting from the newline: W1\n. I often forget this.)