spaces in grep command argument executed in backticks

chilukuri_perl has asked for the wisdom of the Perl Monks concerning the following question:

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Re: spaces in grep command argument executed in backticks by jwkrahn (Abbot) on Oct 22, 2009 at 06:23 UTC
`my $module = 'xyz abc'; open my $PIPE, '-\|', 'ps', '-aef' or die "Cannot open pipe from 'ps' $ +!"; my $pid; while ( <$PIPE> ) { next unless /$module/; $pid = ( split )[ 2 ]; } close $PIPE or warn $! ? "Error closing 'ps' pipe: $!" : "Exit status $? from 'ps'";` [download]	[reply] [d/l]
Re: spaces in grep command argument executed in backticks by cdarke (Prior) on Oct 22, 2009 at 08:03 UTC
The third field of ps -ef is the parent pid, did you mean that? Also, you can avoid the extra `grep -v` with a simple RE trick: $module = "xyz ab[c]"; $pid = `ps -aef\|grep \"$module\"\|cut -d ' ' -f3`; [download] Note the `[ ]` around one of the characters. Back to perl, here is a simple one-liner (OK, three lines) which only creates one child process: my $module = 'xyz abc'; my @ppids = map {(split)[2]} grep /$module/,`ps -ef`; print "@ppids\n"; [download] If you really wanted the pid rather than the ppid then change the `[2]` to `[1]`. Notice that I am using an array, since there might be more than one process which matches.	[reply] [d/l] [select]
Re^2: spaces in grep command argument executed in backticks by jwkrahn (Abbot) on Oct 23, 2009 at 21:01 UTC
my @ppids = map {(split)[2]} grep /$module/,`ps -ef`; [download] my @ppids = map /$module/?(split)[2]:(), `ps -ef`; [download]	[reply] [d/l] [select]
Re: spaces in grep command argument executed in backticks by jakobi (Pilgrim) on Oct 22, 2009 at 07:33 UTC
For a general solution surviving not just embedded blanks, check the recent thread on use variables of system and my reply on secure use here.</p. Then again, you can just move the grep to perl, which takes also care of the issue and allows more powerful regexes. A perl -e "one-liner" example would be e.g. perl -e '$module=$ARGV[0]; @ps=`ps -eaf`; shift @ps if $ps[0]=~/^UID\|^USER/; @ps=grep {/$module/} @ps; $pid=+(split / +/, $ps[0])[1]; warn "pid: $pid"; warn "multiple matches" if $#ps>0; warn @ps' urxvt [download] Wasn't there a module to abstract from or at least parse ps: the ps output if rather inconsistent when comparing e.g. BSD vs SYSV vs GNU...? Just consider the PID field, which for me is the 2nd field. Update: stripped the `and not /grep/` from the grep, claiming shell muscle memory - ps and a lone grep in one line just feel wrong. @jwkrahn thanx for spotting it!	[reply] [d/l] [select]
Re^2: spaces in grep command argument executed in backticks by jwkrahn (Abbot) on Oct 22, 2009 at 07:57 UTC
`@ps=grep {/$module/ and not /grep/} @ps;` [download] Why would you try to match the string `/grep/` when you are using Perl's grep function. That makes no sense at all.	[reply] [d/l] [select]
Re: spaces in grep command argument executed in backticks by Anonymous Monk on Oct 22, 2009 at 06:12 UTC
use single quotes `grep \'$module\'` [download] or alternatively use `$module ="'xyz abc'"` [download]	[reply] [d/l] [select]
Re^2: spaces in grep command argument executed in backticks by Anonymous Monk on Oct 22, 2009 at 06:17 UTC
note:- `grep \'$module\'` [download] can be used without backslashes as `grep '$module'` [download]	[reply] [d/l] [select]