Question

I have a Perl one-liner that works fine on the command line:

perl -nle 'm"\w+:x:\d+:\d+:\S+:/S+:(\S+)$" and $h{$1}++; END{ print "$_: $h{$_}" foreach sort { $h{$b} <=> $h{$a} } keys %h }' /etc/textfile

I’ve put this into a shell file called shell.sh so the next guy won’t have to copy/paste and can just run it:

#!/bin/sh
perl -nle 'm"\w+:x:\d+:\d+:\S+:/S+:(\S+)$" and $h{$1}++; END{ print "$_: $h{$_}" foreach sort { $h{$b} <=> $h{$a} } keys %h }' /etc/textfile

I try running this on the command line and get no results; it just loads a fresh prompt with no output. Anyone see what I’m doing wrong?

Here are some system specs:

Linux version 2.6.32-220.13.1.el6.x86_64

(gcc version 4.4.6 20110731 (Red Hat 4.4.6-3) (GCC)

GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)

Here’s a bit from the text file:

rfink:x:140:140:rat fink:/var/lib/rfink:/sbin/nologin                                 
edible:x:16252:10001:eric idle:/users/eidle/:/bin/bash                                       
tsawyer:x:30855:10001:tom sawyer:/users/tsawyer/:/bin/bash                                
karthur:x:30886:10001:King Arthur:/users/karthur/:/bin/bash                                         
karthur:x:30886:10001:king arthur:/users/karthur/:/bin/bash                                         
jcash:x:30887:10001:john cash:/users/jcash/:/bin/bash                              
hpotter:x:30887:10001:harry potter:/users/hpotter/:/bin/bash                              
triddle:x:30956:10001:tom riddle:/users/triddle/:/bin/bash 

Answer 1

Quick answer

perl -nle 'm"\w+:x:\d+:\d+:[^:]+:\S+:(\S+)\s*$" and $h{$1}++;
  END{ print "$_: $h{$_}" foreach sort { $h{$b} <=> $h{$a} } keys %h }' \
  /etc/textfile

Your regex had three issues.

1. The field after the group ID could have spaces, so replace that subpattern with [^:]+ to match one or more non-colon characters.
2. You used the wrong slash in your subpattern for matching the home directory.
3. Insert \s* before $ to allow optional trailing whitespace on each line.

Output:

/bin/bash: 7
/sbin/nologin: 1

Other approaches

Perl has an awk mode, which would allow

perl -F: -lane '++$sh{$F[-1]};
  END{print "$_: $sh{$_}" for sort { $sh{$b} <=> $sh{$a} } keys %sh}' \
  /etc/textfile

Having to remove trailing whitespace seems to cancel the syntactic benefit.

perl -F: -lane '($sh = pop @F) =~ s/\s+$//; ++$sh{$sh};
  END{print "$_: $sh{$_}" for sort { $sh{$b} <=> $sh{$a} } keys %sh}' \
  /etc/textfile

You could use a pipeline to get the best of all worlds:

perl -pe 's/[^\S\n]+$//' /etc/textfile |
  perl -F: -lane 'print $F[-1]' |
    sort | uniq -c | sort -nr

The output transposes the columns, but you get the same information.

Note the use of the regex double-negative technique in the pipeline’s first command for removing all whitespace except newlines.

      7 /bin/bash
      1 /sbin/nologin

As a shell script

Your question asks for a shell script, so—to vibe off daxim’s answer—that is

#! /bin/sh

perl -MUser::pwent -le \
  '$_->shell && print $_->shell while $_ = getpwent' |
  sort | uniq -c | sort -nr

Note that this does not handle the pathological case of a shell named 0.

If you don’t necessarily want to read the system /etc/passwd, then your script becomes

#! /bin/sh

if [ $# -eq 0 ]; then
  echo Usage: $0 passwd-file .. 1>&2
  exit 1
fi

perl -pe 's/[^\S\n]+$//' "$@" |
  perl -lne 'm|\w+:x:\d+:\d+:[^:]+:\S+:(\S+)$| && print $1' |
    sort | uniq -c | sort -nr

Different systems use different formats, so I recommend nailing down your expectation as in the above rather than blindly printing the last field, whatever it is. This may mean coping with the occasional empty output.