This is part of a homework problem in a beginning bash class.
I need to bring in the passwd file, which I have done with my passfile variable, then I need to be able to extract certain pieces of it and display the different fields. When I manually grep from CLI using this statement below it works fine. I'm wanting all the variables and I get them all.
grep 1000 passfile | cut -c1-
However, when I do this from the script it stops or breaks or starts over at the first 'blank space' in the users full name. John D. Doe will return 3 lines when I only want one. I see this by echoing the value of i and the following.
for i in `grep 1000 ${passfile} | cut -c1-
user=`echo $1 | cut -d : -f1`
userID=`echo $1 | cut -d : -f3`
For example, if the line reads
jdoe:x:123:1000:John D Doe:/home/jdoe:/bin/bash
I get the following:
i = jdoe:x:123:1000:John
which gives me:
User is jdoe, UID is 509
but then in the next line i starts at R.
i = R. so User is R., UID is R.
next line
i = Johnson:/home/jjohnson:/bin/bash
which returns User is Johnson, UID is /bin/bash
The passwd file holds many users so I need to use the for loop to process them all. I think if I can get it to ignore the space I can get it. But not knowing a whole lot about linux, I'm not sure if I'm even going down the right path. Thanks in Advance for guidence/help.
By default, cut splits on spaces, not colons. If you continue to use it, specify the separator.
You probably want to use IFS=: and a read statement in a while loop to get the values in:
while IFS=: read user password uid gid comment home shell
do
...whatever...
done < /etc/passwd
Or you can pipe the output of grep into the while loop.
Are you allowed to use any external program? If so, I'd recommend awk
UID=1000
awkcmd="\$4==\"$UID\" {print \"user:\",\$1}"
cat $PASSWORDFILE | awk -F ":" "$awkcmd"
when parsing structured files with specific field delimiters such as passwd file, the appropriate tool for the job is awk.
UID=1000
awk -vuid="$UID" '$4==uid{print "user: "$1}' /etc/passwd
you do not have to use grep or cut or anything else. ( Of course, you can also use pure bash while read loops as demonstrated.)
Related
I have this exercice :
Create a bash script that check if the user passed as a parameter is
connected and if he is display when he connected. Indications : use the command who, the grep filter and the
command cut.
But i have some trouble to solve it.
#!/bin/bash
who>who.txt;
then
grep $1 who.txt
for a in who.txt
do
echo "$a"
done
else
echo "$1 isnt connected"
fi
So first of all i want to only keep the line where i can find the user in a .txt and then i want to cut each part with a loop in the who command to keep only the date but the problem is that i don't know how to cut here because it's seperated with multiple spaces.
So i'am really blocked and i don't see where to go to do this. I'am a beginner with bash.
If I understand you simply want to check to see if a user is logged in, then that is what the users command is for. If you want to wrap it in a short script, then you could do something like the following:
#!/bin/bash
[ -z "$1" ] && { ## validate 1 argument given on command line
printf "error: insufficient input, usage: %s username.\n" "${0##*/}" >&2
exit 1
}
## check if that argument is among the logged in users
if $(users | grep -q "$1" >/dev/null 2>&1) ; then
printf " user: %s is logged in.\n" "$1"
else
printf " user: %s is NOT logged in.\n" "$1"
fi
Example/Use
$ bash chkuser.sh dog
user: dog is NOT logged in.
$ bash chkuser.sh david
user: david is logged in.
cut is a rather awkward tool for parsing who's output, unless you use fixed column positions. In delimiter mode, with -d ' ', each space makes a separate empty field. It's not like awk where fields are separated by a run of spaces.
who(1) output looks like this (and GNU who has no option to cut it down to just the username/time):
$ who
peter tty1 2015-11-13 18:53
john pts/13 2015-11-12 08:44 (10.0.0.1)
john pts/14 2015-11-12 08:44 (10.0.0.1)
john pts/15 2015-11-12 08:44 (10.0.0.1)
john pts/16 2015-11-12 08:44 (10.0.0.1)
peter pts/9 2015-11-14 16:09 (:0)
I didn't check what happens with very long usernames, whether they're truncated or whether they shift the rest of the line over. Parsing it with awk '{print $3, $4} would feel much safer, since it would still work regardless of exact column position.
But since you need to use cut, let's assume that those exact column positions (time starting from 23 and running until 38) are constant across all systems where we want this script to work, and all terminal widths. (who doesn't appear to vary its output for $COLUMNS or the tty-driver column width (the columns field in stty -a output)).
Putting all that together:
#!/bin/sh
who | grep "^$1 " | cut -c 23-38
The regex on the grep command line will only match at the beginning of the line, and has to match a space following the username (to avoid substring matches). Then those lines that match are filtered through cut, to extract only the columns containing the timestamp.
With an empty cmdline arg, will print the login time for every logged-in user. If the pattern doesn't match anything, the output will be empty. To explicitly detect this and print something else, capture the pipeline output with var=$(pipeline), and test if it's the empty-string or not.
This will print a time for every separate login from the same user. You could use grep's count limit arg (see the man page) to stop after one match, but it might not be the most recent time. You might use sort -n | head -1 or something.
If you don't have to write a loop in the shell, don't. It's much better to write a pipeline that makes one pass over the data. The shell itself is slow, but as long as it doesn't have to parse every line of what you're dealing with, that doesn't matter.
Also note how I quoted the expansion of $1 with double quotes, to avoid the shell applying word splitting and glob expansion to it.
For more shell stuff, see the Wooledge Bash FAQ and guide. That's a good place to get started learning idioms that don't suck (i.e. don't break when you have filenames and directories with spaces in them, or filenames containing a ?, or lines with trailing spaces that you want to not munge...).
I have a situation here.
I have lot of files like below in linux
SIPTV_FIPTV_ID00$line_T20141003195717_C0000001000_FWD148_IPV_001.DATaac
SIPTV_FIPTV_ID00$line_T20141003195717_C0000001000_FWD148_IPV_001.DATaag
I want to remove the $line and make a counter from 0001 to 6000 for my 6000 such files in its place.
Also i want to remove the trailer 3 characters after this is done for each file.
After fix file should be like
SIPTV_FIPTV_ID0000001_T20141003195717_C0000001000_FWD148_IPV_001.DAT
SIPTV_FIPTV_ID0000002_T20141003195717_C0000001000_FWD148_IPV_001.DAT
Please help.
With some assumption, I think this should do it:
1. list of the files is in a file named input.txt, one file per line
2. the code is running in the directory the files are in
3. bash is available
awk '{i++;printf "mv \x27"$0"\x27 ";printf "\x27"substr($0,1,16);printf "%05d", i;print substr($0,22,47)"\x27"}' input.txt | bash
from the command prompt give the following command
% echo *.DAT??? | awk '{
old=$0;
sub("\\$line",sprintf("%4.4d",++n));
sub("...$","");
print "mv", old, $1}'
%
and check the output, if it looks OK
% echo *.DAT??? | awk '{
old=$0;
sub("\\$line",sprintf("%4.4d",++n));
sub("...$","");
print "mv", old, $1}' | sh
%
A commentary: echo *.DAT??? is meant to give as input to awk a list of all the filenames that you want to modify, you may want something more articulated if the example names you gave aren't representative of the whole spectrum... regarding the awk script itself, I used sprintf to generate a string with the correct number of zeroes for the replacement of $line, the idiom `"\\$..." with two backslashes to quote the dollar sign is required by gawk and does no harm in mawk, and as a last remark I have to say that in similar cases I prefer to make at least a dry run before passing the commands to the shell...
I need to manipulate a URL from the values from a file. This is what I could do
var=$(grep -A2 -i "some_text" /path/to/file | grep -v "some_text" | cut -d'"' -f 4-5 | cut -d'"' -f 1 | tr -d '\n')
This will give output : /text/to/be/appended/to/domain
Now, I need to append the domain name to var value.
So I did,
var1="http://mydomain"
and then
echo ${var1}${var}
So I expect
http://mydomain/text/to/be/appended/to/domain
to be the output. But am getting just /text/to/be/appended/to/domain.
I guessed it'd be due to the / as the first char, but if i use cut to remove the first /, am getting value of var1 as output.
Where did I go wrong?
Update (not sure if this would help even a bit, still) :
If I do echo ${var}${var1}, am getting /text/to/be/appended/to/domainhttp://mydomain
Sample entry :
<tr><td><a id="value">some_text</a></td></tr>
<tr><td><a id="value" href="/text/to/be/appended/to/domain">2013</a></td></tr>
this line ending (^M) points that at some point the file was edited(created) in dos like environment. Use "dos2unix yourfile" to fix the problem. BOTH your script and the sample entries.
Okay so what I am trying to figure out is how do I count the number of periods in a string and then cut everything up to that point but minus 2. Meaning like this:
string="aaa.bbb.ccc.ddd.google.com"
number_of_periods="5"
number_of_periods=`expr $number_of_periods-2`
string=`echo $string | cut -d"." -f$number_of_periods`
echo $string
result: "aaa.bbb.ccc.ddd"
The way that I was thinking of doing it was sending the string to a text file and then just greping for the number of times like this:
grep -c "." infile
The reason I don't want to do that is because I want to avoid creating another text file for I do not have permission to do so. It would also be simpler for the code I am trying to build right now.
EDIT
I don't think I made it clear but I want to make finding the number of periods more dynamic because the address I will be looking at will change as the script moves forward.
If you don't need to count the dots, but just remove the penultimate dot and everything afterwards, you can use Bash's built-in string manuipulation.
${string%substring}
Deletes shortest match of $substring from back of $string.
Example:
$ string="aaa.bbb.ccc.ddd.google.com"
$ echo ${string%.*.*}
aaa.bbb.ccc.ddd
Nice and simple and no need for sed, awk or cut!
What about this:
echo "aaa.bbb.ccc.ddd.google.com"|awk 'BEGIN{FS=OFS="."}{NF=NF-2}1'
(further shortened by helpful comment from #steve)
gives:
aaa.bbb.ccc.ddd
The awk command:
awk 'BEGIN{FS=OFS="."}{NF=NF-2}1'
works by separating the input line into fields (FS) by ., then joining them as output (OFS) with ., but the number of fields (NF) has been reduced by 2. The final 1 in the command is responsible for the print.
This will reduce a given input line by eliminating the last two period separated items.
This approach is "shell-agnostic" :)
Perhaps this will help:
#!/bin/sh
input="aaa.bbb.ccc.ddd.google.com"
number_of_fields=$(echo $input | tr "." "\n" | wc -l)
interesting_fields=$(($number_of_fields-2))
echo $input | cut -d. -f-${interesting_fields}
grep -o "\." <<<"aaa.bbb.ccc.ddd.google.com" | wc -l
5
Normally when one wants to look at specific output lines from running something, one can do something like:
./a.out | grep IHaveThisString
but what if IHaveThisString is something which changes every time so you need to first run it, watch the output to catch what IHaveThisString is on that particular run, and then grep it out? I can just dump to file and later grep but is it possible to do something like background it and then bring it to foreground and bringing it back but now piped to some grep? Something akin to:
./a.out
Ctrl-Z
fg | grep NowIKnowThisString
just wondering..
No, it is only in your screen buffer if you didn't save it in some other way.
Short form: You can do this, but you need to know that you need to do it ahead-of-time; it's not something that can be put into place interactively after-the-fact.
Write your script to determine what the string is. We'd need a more detailed example of the output format to give a better example of usage, but here's one for the trivial case where the entire first line is the filter target:
run_my_command | { read string_to_filter_for; fgrep -e "$string_to_filter_for" }
Replace the read string_to_filter_for with as many commands as necessary to read enough input to determine what the target string is; this could be a loop if necessary.
For instance, let's say that the output contains the following:
Session id: foobar
and thereafter, you want to grep for lines containing foobar.
...then you can pipe through the following script:
re='Session id: (.*)'
while read; do
if [[ $REPLY =~ $re ]] ; then
target=${BASH_REMATCH[1]}
break
else
# if you want to print the preamble; leave this out otherwise
printf '%s\n' "$REPLY"
fi
done
[[ $target ]] && grep -F -e "$target"
If you want to manually specify the filter target, this can be done by having the loop check for a file being created with filter contents, and using that when starting up grep afterwards.
That is a little bit strange what you need, but you can do it tis way:
you must go into script session first;
then you use shell how usually;
then you start and interrupt you program;
then run grep over typescript file.
Example:
$ script
$ ./a.out
Ctrl-Z
$ fg
$ grep NowIKnowThisString typescript
You could use a stream editor such as sed instead of grep. Here's an example of what I mean:
$ cat list
Name to look for: Mike
Dora 1
John 2
Mike 3
Helen 4
Here we find the name to look for in the fist line and want to grep for it. Now piping the command to sed:
$ cat list | sed -ne '1{s/Name to look for: //;h}' \
> -e ':r;n;G;/^.*\(.\+\).*\n\1$/P;s/\n.*//;br'
Mike 3
Note: sed itself can take file as a parameter, but you're not working with text files, so that's how you'd use it.
Of course, you'd need to modify the command for your case.