How to extract patterns from a file and replace the multiple patterns with a new pattern from a file? For example: Lets say the pattern file is pattern.txt, as follows with 2,000 lines.
a
b
d
e
f
....
...
...
File to replace pattens is replace.txt containing:
a,1
b,3
c,5
d,10
e,14
....
...
...
The intended final file content for file patterns.txt is:
a,1
b,3
d,10
e,14
....
...
...
Perl from command line,
perl -i -pe'
BEGIN{ local (@ARGV, $/, $^I) =pop; %h = split /[\s,]+/, <> }
s| (\S+)\K |,$h{$1}|x
' pattern.txt replace.txt
It slurps content of second file ($/ to undef), and temporarily disables in-place editing ($^I to undef), splits string on white-spaces/commas and populate %h hash in key/value manner. Then for every line of first file adds comma and value for current key.