strictvars's scratchpad

Public Scratchpad

Idioms:


@hash{@array} = @array;

for (<*.*>) { $totalsize += -s }

@char_num{'A'..'Z'} = 1..26;

print sort <>

@div5 = grep { not $_ % 5} @n;

print map "$_: $h{$_}\n", sort keys %h;
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PERL one-liners

   # run contents of "my_file" as a program 
   perl my_file 

   # run debugger "stand-alone" 
   perl -d -e 42 

   # run program, but with warnings 
   perl -w my_file 

   # run program under debugger 
   perl -d my_file 

   # just check syntax, with warnings 
   perl -wc my_file 

   # useful at end of "find foo -print" 
   perl -nle unlink 

   # simplest one-liner program 
   perl -e 'print "hello world!\n"' 

   # add first and penultimate columns 
   perl -lane 'print $F[0] + $F[-2]' 

   # just lines 15 to 17 
   perl -ne 'print if 15 .. 17' *.pod 

   # in-place edit of *.c files changing all foo to bar 
   perl -p -i.bak -e 's/\bfoo\b/bar/g' *.c 

   # command-line that prints the first 50 lines (cheaply) 
   perl -pe 'exit if $. > 50' f1 f2 f3 ... 

   # delete first 10 lines 
   perl -i.old -ne 'print unless 1 .. 10' foo.txt 

   # change all the isolated oldvar occurrences to newvar 
   perl -i.old -pe 's{\boldvar\b}{newvar}g' *.[chy] 

   # command-line that reverses the whole file by lines 
   perl -e 'print reverse <>' file1 file2 file3 .... 

   # find palindromes 
   perl -lne 'print if $_ eq reverse' /usr/dict/words 

   # command-line that reverse all the bytes in a file 
   perl -0777e 'print scalar reverse <>' f1 f2 f3 ... 

   # command-line that reverses the whole file by paragraphs 
   perl -00 -e 'print reverse <>' file1 file2 file3 .... 

   # increment all numbers found in these files 
   perl i.tiny -pe 's/(\d+)/ 1 + $1 /ge' file1 file2 .... 

   # command-line that shows each line with its characters backwards 
   perl -nle 'print scalar reverse $_' file1 file2 file3 .... 

   # delete all but lines beween START and END 
   perl -i.old -ne 'print unless /^START$/ .. /^END$/' foo.txt 

   # binary edit (careful!) 
   perl -i.bak -pe 's/Mozilla/Slopoke/g' /usr/local/bin/netscape 

   # look for dup words 
   perl -0777 -ne 'print "$.: doubled $_\n" while /\b(\w+)\b\s+\b\1\b/
+gi' 

   # command-line that prints the last 50 lines (expensively) 
   perl -e 'lines = <>; print @@lines[ $#lines .. $#lines-50' f1 f2 f3
+ ...
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printf examples

 print ":1234567890:\n";
 printf ":%7s:\n", "abcdefghij";     # min width, string is longer
 printf ":%7s:\n", "abc";            # min width, string is shorter ri
+ght align
 printf ":%-7s:\n", "abc";           # min width, string is shorter le
+ft align
 print "---\n";
 printf ":%.7s:\n", "abc";           # max width, string is shorter
 printf ":%.7s:\n", "abcdefghij";    # max width, string is longer
 print "---\n";
 printf ":%7.7s:\n", "abcdefghij";   # min.max and they are the same
 printf ":%7.7s:\n", "abc";          # min.max and they are the same
 print "---\n";
 printf ":%3d:\n", 3;                # min width
 printf ":%0.3d:\n", 3;              # min width with 0 padding
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Results:

 :1234567890:
 :abcdefghij:
 :    abc:
 :abc    :
 ---
 :abc:
 :abcdefg:
 ---
 :abcdefg:
 :    abc:
 ---
 :  3:
 :003:
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