awk question
2007-12-25 9:37:00
responded to my "silly" awk syntax question. Below
is the summary:
Original Question:
I'm not too familiar with awk, and I'm just trying to
get the home directory of a given user (to put it in
a shell script)
using awk (or sed... it doesn't matter which).
Anyhow, I'm trying to use split or FS to tell it to
user ":" as the
delimiter, but neither seems to work for me:
#grep oracle /etc/passwd
#oracle:x:301:204::/u01/oracle:/bin/tcsh
user=oracle
homedir=`grep $user /etc/passwd | awk '
BEGIN {
split($0, field, ":")
print field[5]
}'`
echo "$user (home directory) = $homedir"
# I also tried the following:
# grep $user /etc/passwd | awk '{ FS = ":"; print
$5"\n"}'
Summary:
I made 3 mistakes:
1. The syntax for awk is something like
reg-expr { commands}
BEGIN is a special regular expression that excutes
it's associated commands BEFORE any input lines are
read.
2. FS needs to be set on the command line as an
arguemnt to awk. (or as one of the commands executed
by the BEGIN section.)
3. It's field 6 not 5... (I'm thinking in C, i.e.
things start from subscript 0! Oh well...)
The following are some of the solutions people
recommended:
OPTION 1: Using getent, you will get the entry line
for the user
no matter if it is a local user, or defined in nis or
nis+ tables.
getent passwd $user | cut -f 6 -d ":"
**********************
OPTION 2: If you preffer using grep, you still can do
it,
but you restrict your search to local users:
grep $user /etc/passwd | cut -f6 -d ":"
***********************
OPTION 3: using awk and getent command
getent passwd $user | awk -F: '{print $6}'
***********************
OPTION 4: Using awk and checking directly in the file
grep $user /etc/passwd | awk -F: '{print $6}'
or
awk -F: ' /^oracle/ {print $6}' </etc/passwd
or
grep ^$username: /etc/passwd |awk -F: '{print $5}'
You want the ^ at the front of $username so that it
will match only at the START of a line, and the : at
the end so it
matches the ":" separator. This way it will match
bin: rather than foobin or foobin1 for the username...
or
nawk -F\: '{print $6}' /etc/passwd
or
awk -F: '$1 == user {print $6}' user=$user <
/etc/passwd
The -F: tells awk to use ":" as delimiter.
The "user=$user" as last argument imports the shell
variable $user as
awk variable user.
<You could also program in ksh, and just use ~user.>
user=oracle
homedir=`grep $user /etc/passwd | awk '
BEGIN { FS = ":" }
{ print $5 }'`
echo "$user (home directory) = $homedir"
or
grep "^oracle:" /etc/passwd | awk 'BEGIN { FS=":" }
{ print $6 }'
or
grep $user /etc/passwd | awk '{FS=":"; print $6}'
---
you must use BEGIN when you try to declare that your
field separator is
:
so this is the complete script that you want
set user=oracle
set homedir=`grep $user /etc/passwd|nawk 'BEGIN
{FS=":"} {print $6}'`
---
both csh and ksh understand ~<uid> (which they expand
to home of <uid>). One way that this will work
transparently with nis is:
homedir=`/bin/csh -fc "echo ~$user"`
---
# grep $user /etc/passwd | nnawk ' BEGIN { FS=":" }
{ print $5 } '
this will print the fifth field of the password file.
where fields (FS) are separated by a colon. you need
to specify the value of FS in the begin section,
otherwise it gets overwritten in each line.
you can also use the -v option to just have one
command instead of two (grep and awk)
awk -vUSR=$user ' BEGIN { FS=":" } { if ($1==USR)
print $5 } '
/etc/passwd
this is fairly well documented in the man page for
nawk.
Ju
_________________________________________________________
DO YOU YAHOO!?
Get your free @yahoo.com address at http://mail.yahoo.com
Comments
Got something to say?
You must be logged in to post a comment.
