Programmatically read from STDIN or input file in Perl

Question

What is the slickest way to programatically read from stdin or an input file  if provided  in Perl

User · Answer

if my  file   shift      if file is specified  read from that   open my  fh    lt     file  or die        while my  line    lt  fh gt         print  line        else     otherwise  read from STDIN   print while  lt  gt

User · Answer

The  slickest  way in certain situations is to take advantage of the -n switch   It implicitly wraps your code with a while  lt  gt   loop and handles the input flexibly   In slickestWay pl       usr bin perl -n  BEGIN        do something once here      implement logic for a single line of input print  result    At the command line   chmod  x slickestWay pl   Now  depending on your input do one of the following    Wait for user input    slickestWay pl  Read from file s  named in arguments  no redirection required     slickestWay pl input txt   slickestWay pl input txt moreInput txt  Use a pipe  someOtherScript     slickestWay pl     The BEGIN block is necessary if you need to initialize some kind of object-oriented interface  such as Text  CSV or some such  which you can add to the shebang with -M   -l and -p are also your friends

User · Answer

This provides a named variable to work with   foreach my  line    lt STDIN gt          chomp   line        print   line n       To read a file  pipe it in like this   program pl  lt  inputfile

User · Answer

If there is a reason you can t use the simple solution provided by ennuikiller above  then you will have to use Typeglobs to manipulate file handles  This is way more work  This example copies from the file in  ARGV 0  to that in  ARGV 1   It defaults to STDIN and STDOUT respectively if files are not specified   use English   my  in  my  out   if    ARGV  gt   0       unless  open  in     lt     ARGV 0           die  could not open  ARGV 0  for reading            else        in     STDIN     if    ARGV  gt   1       unless  open  out    gt     ARGV 1           die  could not open  ARGV 1  for writing            else        out     STDOUT     while        lt  in gt         out- gt print

User · Answer

Here is how I made a script that could take either command line inputs or have a text file redirected    if    ARGV  lt  1         ARGV            ARGV    lt  gt       chomp  ARGV        This will reassign the contents of the file to  ARGV  from there you just process  ARGV as if someone was including command line options    WARNING   If no file is redirected  the program will sit their idle because it is waiting for input from STDIN    I have not figured out a way to detect if a file is being redirected in yet to eliminate the STDIN issue

User · Answer

You need to use  lt   operator   while   lt  gt         print       or simply  print       Which can be compacted to   print while   lt  gt      Arbitrary file   open F    lt file txt  or die     while   lt F gt         print       close F

User · Answer

Do   userinput     lt STDIN gt    read stdin and put it in  userinput chomp   userinput       cut the return   line feed character   if you want to read just one line

User · Answer

while   lt  gt     print      will read either from a file specified on the command line or from stdin if no file is given  If you are required this loop construction in command line  then you may use -n option     perl -ne  print     Here you just put code between    from first example into    in second

[perl] Programmatically read from STDIN or input file in Perl

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