Need to grep for first initial and lastname

[Allanm]

I have a list of username in the form of -

firstname_lastname and I need the date in this form -

f_lastname

How shall I go about getting this.

Thanks,
Allan.

[Allanm]

date=data

[Matti_Kurkela · Accepted solution]

One username on each line, and nothing else on the lines?

sed -e 's/^\(.\)[^_]*_\(.*\)$/\1_\2/g' < firstname_lastname.txt > f_lastname.txt

This is a regular expression, which tends to look a bit cryptic. (Someone has said they tend to be Write-Only.)

So here's it split into meaningful parts:

s/ ... / ... /g = the global search-and-replace command, probably the most often-used command of sed.

The search expression:

^ = from the beginning of a line...

\(.\) = ...take a single character and remember it...

[^_]*_ = ...which is followed by any number of non-underscore characters, followed by a single underscore.

\(.*\)$ = After the underscore, take everything and remember it too.

The replacement expression:

\1_\2 = The first thing we asked sed to remember, followed by an underscore and the second thing.

MK

[Marco A.]

I needed to do something similar, and this reg expression works for me too, thanks!

Marco,

[James R. Ferguson]

Hi Allan:

# X="firstname_lastname"
# echo ${X}|perl -ple 's/^(.)(?:.+?)(_.+)/$1$2/'

f_lastname

Regards!

...JRF...

[Suraj K Sankari]

Hi,

You can do it like this way also
awk 'BEGIN { FS = "_" } ; { print substr($0,1,1)"_"$2 }' output file

Suraj