parallel: added --tagstring + man + test.

parallel.pod: Elaborated on problems with -u.

src/parallel

@@ -705,6 +705,9 @@ sub parse_options {
 	$Global::replace{$_} = ::maybe_quote($Global::replace{$_});
     }
     %Global::replace_rev = reverse %Global::replace;
+    if(defined $::opt_tag and not defined $::opt_tagstring) {
+	$::opt_tagstring = $Global::replace{'{}'};
+    }
 
     if(grep /^$Global::arg_sep$|^$Global::arg_file_sep$/o, @ARGV) {
         # Deal with ::: and ::::
@@ -3728,13 +3731,8 @@ sub print {
 sub tag {
     my $self = shift;
     if(not defined $self->{'tag'}) {
-	$self->{'tag'} = "";
-	if(defined $::opt_tagstring) {
-	    $self->{'tag'} .= $::opt_tagstring."\t";
-	}
-	if(defined $::opt_tag) {
-	    $self->{'tag'} .= $self->{'commandline'}->args_as_string()."\t";
-	}
+	$self->{'tag'} = $self->{'commandline'}->
+	    replace_placeholders($::opt_tagstring,0)."\t";
     }
     return $self->{'tag'};
 }
@@ -3798,9 +3796,20 @@ sub new {
 	    # Add {} to the command if there are no {...}'s
 	    $command .=" ".$Global::replace{'{}'};
         }
+	($sum,$len->{'no_args'},$len->{'context'},$len->{'contextgroups'},
+	 %replacecount) = number_of_replacements($command,$context_replace);
     }
-    ($sum,$len->{'no_args'},$len->{'context'},$len->{'contextgroups'},
-     %replacecount) = number_of_replacements($command,$context_replace);
+    if(defined $::opt_tagstring) {
+	my ($dummy1,$dummy2,$dummy3,$dummy4,%repcount) =
+	    number_of_replacements($::opt_tagstring,$context_replace);
+	# Merge %repcount with %replacecount to get the keys
+	# for replacing replacement strings in $::opt_tagstring
+	# The number, however, does not matter.
+	for (keys %repcount) {
+	    $replacecount{$_} ||= 0;
+	}
+    }
+
     my %positional_replace;
     my %multi_replace;
     for my $used (keys %replacecount) {

src/parallel.pod

@@ -1200,6 +1200,15 @@ the lines will be prepended with the sshlogin instead.
 B<--tag> is ignored when using B<-u>.
 
 
+=item B<--tagstring> I<str>
+
+Tag lines with a string. Each output line will be prepended with
+I<str> and TAB (\t). I<str> can contain replacement strings such as
+{}.
+
+B<--tagstring> is ignored when using B<-u>, B<--onall>, and B<--nonall>.
+
+
 =item B<--tmpdir> I<dirname>
 
 Directory for temporary files. GNU B<parallel> normally buffers output
@@ -1295,9 +1304,16 @@ a bc " -> "a bc". This is the default if B<--colsep> is used.
 
 =item B<-u>
 
-Ungroup output.  Output is printed as soon as possible. This may cause
-output from different commands to be mixed. GNU B<parallel> runs
-faster with B<-u>. Can be reversed with B<--group>.
+Ungroup output.  Output is printed as soon as possible and by passes
+GNU B<parallel> internal processing. This may cause
+output from different commands to be mixed. Compare these:
+
+B<parallel -j0 'sleep {};echo -n start{};sleep {};echo {}end' ::: 1 2 3 4>
+
+B<parallel -u -j0 'sleep {};echo -n start{};sleep {};echo {}end' ::: 1 2 3 4>
+
+It also disables B<--tag>. GNU B<parallel> runs faster with B<-u>. Can
+be reversed with B<--group>.
 
 
 =item B<--extensionreplace> I<replace-str>

src/parallel.texi

@@ -1279,6 +1279,15 @@ the lines will be prepended with the sshlogin instead.
 
 @strong{--tag} is ignored when using @strong{-u}.
 
+@item @strong{--tagstring} @emph{str}
+@anchor{@strong{--tagstring} @emph{str}}
+
+Tag lines with a string. Each output line will be prepended with
+@emph{str} and TAB (\t). @emph{str} can contain replacement strings such as
+@{@}.
+
+@strong{--tagstring} is ignored when using @strong{-u}, @strong{--onall}, and @strong{--nonall}.
+
 @item @strong{--tmpdir} @emph{dirname}
 @anchor{@strong{--tmpdir} @emph{dirname}}
 
@@ -1385,9 +1394,16 @@ a bc " -> "a bc". This is the default if @strong{--colsep} is used.
 @item @strong{-u}
 @anchor{@strong{-u}}
 
-Ungroup output.  Output is printed as soon as possible. This may cause
-output from different commands to be mixed. GNU @strong{parallel} runs
-faster with @strong{-u}. Can be reversed with @strong{--group}.
+Ungroup output.  Output is printed as soon as possible and by passes
+GNU @strong{parallel} internal processing. This may cause
+output from different commands to be mixed. Compare these:
+
+@strong{parallel -j0 'sleep @{@};echo -n start@{@};sleep @{@};echo @{@}end' ::: 1 2 3 4}
+
+@strong{parallel -u -j0 'sleep @{@};echo -n start@{@};sleep @{@};echo @{@}end' ::: 1 2 3 4}
+
+It also disables @strong{--tag}. GNU @strong{parallel} runs faster with @strong{-u}. Can
+be reversed with @strong{--group}.
 
 @item @strong{--extensionreplace} @emph{replace-str}
 @anchor{@strong{--extensionreplace} @emph{replace-str}}

testsuite/tests-to-run/parallel-local150.sh

@@ -2,3 +2,10 @@
 
 echo '### Test fix #32191'
 seq 1 150 | parallel -j9 --retries 2 -S localhost,: "/bin/non-existant 2>/dev/null"
+
+echo '### Test --tagstring'
+parallel -j1 -X -v --tagstring a{}b echo  ::: 3 4
+parallel -j1 -k -v --tagstring a{}b echo  ::: 3 4
+parallel -j1 -k -v --tagstring a{}b echo job{#} ::: 3 4
+parallel -j1 -k -v --tagstring ajob{#}b echo job{#} ::: 3 4
+

testsuite/wanted-results/parallel-local150

@@ -1 +1,16 @@
 ### Test fix #32191
+### Test --tagstring
+echo 3 4
+a3b a4b	3 4
+echo 3
+a3b	3
+echo 4
+a4b	4
+echo job1
+a3b	job1
+echo job2
+a4b	job2
+echo job1
+ajob1b	job1
+echo job2
+ajob2b	job2