Redirect Perl command output to file

Question

In a bash script, I try to call the following Perl command on each file, and then I want to redirect the Perl command's output to that file.

The Perl command simply removes the comments from the file. When it prints to the console it seems to work. But when I try to redirect the output to each individual file, the file becomes empty. What am I doing wrong here?

#!/usr/bin/env bash

shopt -s globstar
for file in ./**/*.java; do
    perl -0pe 's|//.*?\n|\n|g; s#/\*(.|\n)*?\*/##g; s/\n\n+/\n\n/g' "$file" > "$file";
done

Tip: -0 doesn't actually slurp the file. You should use -0777 instead. — ikegami
– ikegami, Commented Dec 27, 2017 at 7:58
@ikegami How was it able then to process the file not line by line? — rapt
– rapt, Commented Dec 27, 2017 at 8:21
Read up on the difference between $/ = "\0"; (-0) and $/ = undef; (-0777). It's not the intent of the first to slurp (and won't always). — ikegami
– ikegami, Commented Dec 29, 2017 at 10:41

Guru · Accepted Answer · 2017-12-27 07:45:29Z

2

You are trying to read from a file and trying to re-direct the output to the same file. This does not work. Shell first opens the file for writing, now when Perl tries to read from the file, there is nothing present, and hence no output.

You can use the -i option of Perl to do in-place edit.

perl -i.bak -0pe 's|//.*?\n|\n|g; s#/\*(.|\n)*?\*/##g; s/\n\n+/\n\n/g' "$file"

This will edit the file directly and also have the original copy of the file with a .bak extension. If you do not need any backup, simply use -i in place of -i.bak

edited Dec 27, 2017 at 7:45

answered Dec 27, 2017 at 7:39

Guru

17.1k2 gold badges37 silver badges47 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

rapt Over a year ago

Thank you! Now it makes sense!

Collectives™ on Stack Overflow

Redirect Perl command output to file

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related