perl's substitution operator "s" with file contents?

Shell Programming and Scripting
1

Please show me how to make substitution over the contents of a file in a perl script.

In a perl script, the core part of substitution operation is

s/FINDPATTERN/REPLACEPATTERN/g;

However, I cannot figure out how to make the substitution occur over the contents of a file. The following perl script failed by syntax error.

#!/usr/bin/perl
use strict;
use warnings;
s/FINDPATTERN/REPLACEPATTERN/g  FILE;

The substitution over the contents of a file involves reading and writing of the file. I do not know how to connect the substitution to the reading and writing of a file.

2

If the substitution is the only operation that you want to perform on the file, then you can use this on the command line:

perl -i -0pe 's/FINDPATTERN/REPLACEPATTERN/g' file
3

No, my perl script is supposed to grow with more statements. I would like all the operations to be done inside a perl script.

4 
$
$ # display the data file
$ cat -n data_file
    1  this is line 1
    2  this is line 2
    3  i want to substitute this => ~ <= by that => # <=
    4  at multiple places => abc~ def~ghi ~~jkl ~~
    5  in multiple lines => ~
    6  and here ~
    7  and here as well ~
    8  this is line 8
    9  and this is the last line...
$
$ # show the Perl program to update the data file
$ cat -n update_data_file.pl
    1  #!/usr/bin/perl -w
    2  use strict;
    3  my $old = "data_file";      # the data file
    4  my $new = "data_file.new";  # a new/temporary file, which will be moved to $old
    5  open(OLD, "<", $old)      or die "can't open $old: $!";
    6  open(NEW, ">", $new)      or die "can't open $new: $!";
    7  while (<OLD>) {
    8    s/~/#/g;                  # globally replace ~ by # in the current line
    9    print NEW $_;             # print the updated line to new/temporary file
   10  }
   11  close(OLD)                or die "can't close $old: $!";
   12  close(NEW)                or die "can't close $new: $!";
   13  # back up the $old file and rename the new/temporary file to $old
   14  rename($old, "$old.orig") or die "can't rename $old to $old.orig: $!";
   15  rename($new, $old)        or die "can't rename $new to $old: $!";
$
$ # run the Perl program
$ perl update_data_file.pl
$
$ # check the updated data file
$ cat -n data_file
    1  this is line 1
    2  this is line 2
    3  i want to substitute this => # <= by that => # <=
    4  at multiple places => abc# def#ghi ##jkl ##
    5  in multiple lines => #
    6  and here #
    7  and here as well #
    8  this is line 8
    9  and this is the last line...
$
$ # check the backup file
$ cat -n data_file.orig
    1  this is line 1
    2  this is line 2
    3  i want to substitute this => ~ <= by that => # <=
    4  at multiple places => abc~ def~ghi ~~jkl ~~
    5  in multiple lines => ~
    6  and here ~
    7  and here as well ~
    8  this is line 8
    9  and this is the last line...
$
$

tyler_durden

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