-Many oneliners rely on the magic of [Perl]'s __ -i__ switch, which means when files supplied on the commandline are opened they are edited in place, and if an extension was passed, a backup copy with that extension will be made. __ -e__ specifies the [Perl] code to run. See perlrun(1) for any other switches used here - in particular, __ -n__ and __ -p__ make powerful allies for __ -i__ . 

- perl -ni.bak -e'/\S/ && print' file1 file2 

- for FILE in file1 file2 ; do mv "$F"{,.bak} ; grep '[ [^ ]' "$F.bak" > "$F" ; done 

- perl -00 -pi.bak -e1 file1 file2 

-Note the use of __ 1__ as a no-op piece of Perl code. In this case, the __ -00__ and __ -p__ switches already do all the work, so only a dummy needs to be supplied. 

- perl -e 'printf "%08b\n", $_ for unpack "C*", shift' 'My String' 

- perl -pe 's!\\n!\n!g; s!\\t!\t!g' $file 

-Note that you can use any punctuation as the separator in an __ s///__ command, and if you have backslashes or even need literal slashes in your pattern then doing this can increase clarity. 

- perl -0777 -pe 'BEGIN { chdir "/proc"; @ARGV = sort { $a <=> $b } glob("*/cmdline") }  

- $ARGV =~ m!^(\d+)/!; print "$1\t"; s/\/ /g; $_ .= "\n";' 

-It runs an implicit loop over the __ /proc/*/cmdline__ files, by priming __ @ARGV__ with a list of files sorted numerically (which needs to be done explicitly using __ <=>__ -- the default sort is [ASCII]betical) and then employing the __ -p__ switch. __ -0777__ forces files to be slurped wholesale. Per file, the digits that lead the filename are printed, followed by a tab. Since a null separates the arguments in these files, all of them are replaced by spaces to make the output printable. Finally, a newline is appended. The print call implicit in the __ -p__ switch then takes care of outputting the massaged command line. 

- perl -MFile::Slurp -0le 'for(sort { $a <=> $b } grep !/\D/, read_dir "/proc")  

- { @ARGV = "/proc/$_/cmdline"; printf " %6g %s\n", $_, join(" ", <>); }' 

-This time the loop is explicit. Again, there are two parts to the program -- selecting files and doing [IO ] on them. 

-To read the directory, a convenience function is pulled in from the File::Slurp module, loaded using the __ -M__ switch. The module has been part of the core distribution since Perl 5.8.. Reading a directory manually is straightforward but the code would be longer and clumsier. 

-Selecting the files is pretty simple, if a little obtuse: it's done by reading the contents of __ /proc__ , then using __ grep !/D/__ to reject any entries that contain non-digit characters from the list. The results are then sorted numerically, which needs to be done explicitly using the __ <=>__ operator because the default sort is [ASCII]betical. Each entry is then interpolated into a full path and stuck into __ @ARGV__ one by one, from where the __ <>__ "diamond operator" will pick it up, auto-open it and read it for us, even autoreporting any errors in a nicely verbose format. 

-Producing human-readable output is a little more involved, using switches to abbreviate a bit of magic. The __ -__ switch sets the __ $/__ variable: here, because the switch is not followed by a digit, it sets the variable to a null character. This means that null characters will be regarded as line separators on input. The __ -l__ switch has two effects, of which only one is relevant to us: it automatically removes line terminators from lines read using the diamond operator. (The other is to set the __ $\__ variable, which we aren't interested in or affected by.) 

-;: Note that the __ -__ and __ -l__ switches are order sensitive both in syntax and semantics. We order them for syntax here, because they can both accept an octal number as input, but we don't to pass one to either of them (particularly, __ -__ will be mistaken for a digit parameter to __ -l__ if we turn them around). 

-Together, these switches effectively mean that we get null terminated lines from files, with the nulls removed on input. So we get the command line arguments listed in a __ /proc/*/cmdline__ file as nice list of separate strings. And because __ join()__ expects a list, __ <>__ returns all "lines" (ie command line arguments) at once, which __ join()__ then dutifully puts together with spaces between.