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Full Discussion: Understanding an example of perl map() function
Top Forums Shell Programming and Scripting Understanding an example of perl map() function Post 303003539 by yifangt on Friday 15th of September 2017 12:18:43 PM
Old 09-15-2017
Understanding an example of perl map() function
Hello,
I have many folders under which there is always a file with the same name, which contains the data I need to process later. A perl oneliner was borrowed
Code:
perl -e 'print "gene_id\t", join("\t", map {/(.*)\//; $1} @ARGV),"\n";' *_test.trim/level.csv

to make a header so that each column corresponding to the respective folder to distinguish the same file names for later processing. The directory structure looks like this:
Code:
1_test.trim/level.csv
15_test.trim/level.csv
17_test.trim/level.csv
30_test.trim/level.csv
34_test.trim/level.csv
8_test.trim/level.csv

The output is:
Code:
gene_id    1_test    15_test    17_test    30_test    34_test    8_test

I had hard time to understand the $1 within the map() function in the oneliner.
I think I understand what the map() and join() functions in perl, but this $1 tripped me quite hard.
(.*)\/ is the regex which is to get rid of the .trim/ part, I believe, but then comes the $1. Maybe, the whole part of map {/(.*)\//; $1} is doing something that I did not catch.
I appreciate any explanation for me.
Last edited by yifangt; 09-15-2017 at 01:31 PM..
 

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LEARN ABOUT DEBIAN

speedy_backend

SPEEDY_BACKEND(1p)														SPEEDY_BACKEND(1p)

NAME

       speedy_backend - the backend process for a persistent Perl interpreter

SYNOPSIS

       none ; this program is not meant to be called directly.

DESCRIPTION

       speedy, short for SpeedyCGI, is a way to run perl scripts persistently, which can make them run much more quickly.

       After the script is initially run, instead of exiting, the perl interpreter is kept running inside a backend process, speedy_backend.  Dur-
       ing subsequent runs, this interpreter is used to handle new executions instead of starting a new perl interpreter each time.  A	very  fast
       frontend  program, speedy, written in C, is executed for each request.  This fast frontend then contacts the persistent Perl process, which
       is usually already running, to do the work and return the results.

       Each perl script runs in its own Unix process, so one perl script can't interfere with another.	Command line options can also be  used	to
       deal with programs that have memory leaks or other problems that might keep them from otherwise running persistently.

       The speedy front end connects to the back end process, speedy_backend, via a Unix socket in /tmp.  A queue is kept in a shared file in /tmp
       that holds an entry for each process.  In that queue are the pids of the perl processes waiting for  connections.   The	frontend  pulls  a
       process	out  of this queue, connects to its socket, sends over the environment and argv, and then uses this socket for stdin/stdout to the
       perl process.

FILES

       /tmp/speedy* A unix socket used to connect to the frontend process.

AUTHOR

	       Sam Horrocks
	       http://daemoninc.com
	       sam@daemoninc.com

NOTES

       This manual page was created by Niko Tyni <ntyni@iki.fi> for Debian GNU/Linux, because the original program does not have one. It is  based
       on the original and more complete CGI::SpeedyCGI(3pm) manual page.

SEE ALSO

       perl(1), CGI::SpeedyCGI(3pm), speedy(1)

																SPEEDY_BACKEND(1p)
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