Removing columns and sorting by Name in finger command - linux

Question

When I use the finger command, it displays Login, Name, Tty, Idle, Login Time, Office, Office Phone, and Host. I just need the information in the Login, Name, Idle, and Login Time columns.
I tried using awk and sed, but they resulted in chart being all over the place (example below).
$ finger | sed -r 's/\S+//3'
Login Name Idle Login Time Office Office Phone Host
user1 Full Name pts/1 20 Feb 3 19:34 (--------------------)
user2 FirstName LastName pts/2 Feb 3 17:04 (--------------)
user3 Name NameName pts/3 1:11 Feb 2 11:37 (-------------------------------)
user4 F Last pts/4 1:09 Feb 13 18:14 (-------------------)
How do I go about removing specific columns while keeping the structure intact?

Answer 1

The problem here is that you cannot extract particular fields based on whitespace separator, because on certain rows the columns might be blank and contain only whitespace, especially the Idle column, which will be blank for sessions with limited idle time. (An additional problem is that the real name field may contain a variable number of spaces.)
So you may have to resort to cut -b ... using hard-coded byte offsets. The following seems to work on my system, as finger seems to use a fixed format output, truncating real names etc as needed, so the byte offsets do not change if the length of the GECOS (real name) field of logged in users is changed.
finger | cut -b 1-20,30-48
Note that it will be inherently fragile if the format of the finger command output were to change in future. You might be able to produce something slightly more robust using regular expression parsing, for example parsing the column headings (first line of finger output) to obtain the byte offsets rather than hard-coding them, but it will still be somewhat fragile. A more robust solution would involve writing your own code to obtain information from the same sources that finger uses, and use that in place of finger. The existing code of an open-source implementation of finger might be a suitable starting point, and then you can adapt it to remove the columns that are not of interest.
Update: building a patched version of finger.
Save this patch as /tmp/patch. It it just a quick-and-dirty patch to suppress certain fields from being printed; they are still calculated.
--- sprint.c~ 2020-06-13 12:27:12.000000000 +0100
+++ sprint.c 2020-06-13 12:32:23.363138500 +0100
## -89,7 +89,7 ##
if (maxlname + maxrname < space-2) { maxlname++; maxrname++; }
(void)xprintf("%-*s %-*s %s\n", maxlname, "Login", maxrname,
- "Name", " Tty Idle Login Time Office Office Phone");
+ "Name", " Idle Login Time");
for (cnt = 0; cnt < entries; ++cnt) {
pn = list[cnt];
for (w = pn->whead; w != NULL; w = w->next) {
## -100,12 +100,6 ##
(void)xprintf(" * * No logins ");
goto office;
}
- (void)xputc(w->info == LOGGEDIN && !w->writable ?
- '*' : ' ');
- if (*w->tty)
- (void)xprintf("%-7.7s ", w->tty);
- else
- (void)xprintf(" ");
if (w->info == LOGGEDIN) {
stimeprint(w);
(void)xprintf(" ");
## -118,17 +112,6 ##
else
(void)xprintf(" %.5s", p + 11);
office:
- if (w->host[0] != '\0') {
- xprintf(" (%s)", w->host);
- } else {
- if (pn->office)
- (void)xprintf(" %-10.10s", pn->office);
- else if (pn->officephone)
- (void)xprintf(" %-10.10s", " ");
- if (pn->officephone)
- (void)xprintf(" %-.14s",
- prphone(pn->officephone));
- }
xputc('\n');
}
}
Then obtain the source code, patch it and build it. (Change destdir as required.)
apt-get source finger
cd bsd-finger-0.17/
pushd finger
patch -p0 < /tmp/patch
popd
destdir=/tmp/finger
mkdir -p $destdir/man/man8 $destdir/sbin $destdir/bin
./configure --prefix=$destdir
make
make install
And run it...
$destdir/bin/finger

Answer 2

Basically, to treat columns, awk is the way to go,
ex: remove third column
finger | awk '{$3="";print}'

Answer 3

Another way: If you found this informations, they have to be wrote somewhere in the system. Using who, awk and cut :
The informations can be gathered by getent passwd.
Created a test user with adduser :
# adduser foobar
Adding user `foobar' ...
Adding new group `foobar' (1001) ...
Adding new user `foobar' (1001) with group `foobar' ...
Creating home directory `/home/foobar' ...
Copying files from `/etc/skel' ...
New password:
Retype new password:
passwd: password updated successfully
Changing the user information for foobar
Enter the new value, or press ENTER for the default
Full Name []: Jean-Charles De la tour
Room Number []: 42
Work Phone []: [phone]
Home Phone []: [phone]
Other []: sysadmin
Is the information correct? [Y/n] Y
And the new line in /etc/passwd file:
foobar:x:1001:1001:Jean-Charles De la tour,42,[phone],[phone],sysadmin:/home/foobar:/bin/bash
So it's easy to retrieve in formations from this:
for u in $(who | cut -d' ' -f1); do # iterate over connected users
getent passwd | awk -F'[:,]' -v OFS='\n' -v u="$u" '$1==u{print "user: "$1, "full name: "$5, "room: "$6, "work phone : "$7, "home phone: "$8, "other: "$9}'
done
Just make sure you have , in $5 column.
Output
user: foobar
full name: Jean-Charles De la tour
room: 42
work phone : [phone]
home phone: [phone]
other: sysadmin