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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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