Replace a string in file with new string containing $ sign in Perl

Question

I am trying to replace string with a new string containing $(dollar) sign in a existing file.

I have used below (regex) line in my code but I am not able get the expected result. Please suggest the solution.

system("perl -pi -e \"s/length\\s+.*/length [index $pkt_len]/g if /^\\s*set_value\\s+length/\" $filename")

set_value length 1 . Instead of $ symbol its value is printed — Unknown
– Unknown, Commented May 25, 2020 at 8:36
Instead of calling a new perl process from within a perl process, you could also do everything in the first perl. Please show the content of the file $filename, the value of $pkt_len and what should be the expected output (the new content of $filename) — Håkon Hægland
– Håkon Hægland, Commented May 25, 2020 at 13:50
Not that you should do this, but it you want to call perl from within a Perl program, you should use $^X. That's the current perl binary that's running. If plain perl finds another one in your path but uses your current environment, you can get mismatches in library versions. — brian d foy
– brian d foy, Commented May 25, 2020 at 16:11
in the $filename i want to replace "set_value length 1" string with "set_value length [index $pkt_len]". i am able to replace but instead of $ symbol it's value is appearing in the file. — Unknown
– Unknown, Commented May 26, 2020 at 5:32

Georg Mavridis · Accepted Answer · 2020-05-26 10:16:23Z

1

The way to find the solution is during debug you should print out the line of the system call and test it "by hand" if it works as expected in the shell.

My guess is that

system("perl -pi -e 's/length\\s+.*/length [index \\\$pkt_len]/g if /^\\s*set_value\\s+length/' $filename")

is a solution.

answered May 26, 2020 at 10:16

Georg Mavridis

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Håkon Hægland · Accepted Answer · 2020-05-26 10:45:49Z

1

You need 7 backslashes (!):

system("echo a | perl -pe \"s/a/\\\\\\\$foo/\"");

Output:

$foo

First "echo a | perl -pe \"s/a/\\\\\\\$foo/\"" is interpreted by perl which reduces the string to echo a | perl -pe "s/a/\\\$foo/"
Then it is parsed by the shell sh to give : echo a | perl -pe s/a/\$foo/
Finally, it is parsed by perl a second time to give the output $foo.

edited May 26, 2020 at 10:45

answered May 26, 2020 at 10:39

Håkon Hægland

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