[perl-python] 20050126 find replace strings in file

Discussion in 'Python' started by Xah Lee, Jan 26, 2005.

  1. Xah Lee

    Xah Lee Guest

    © # -*- coding: utf-8 -*-
    © # Python
    © import sys
    © nn = len(sys.argv)
    © if not nn==5:
    © print "error: %s search_text replace_text in_file out_file" %
    © else:
    © stext = sys.argv[1]
    © rtext = sys.argv[2]
    © input = open(sys.argv[3])
    © output = open(sys.argv[4],'w')
    © for s in input:
    © output.write(s.replace(stext,rtext))
    © output.close()
    © input.close()

    save this code as find_replace.py
    run it like this:
    python find_replace.py findtext replacetext in_file out_file

    the sys.argv is from sys. sys.argv[0] is the program's name itself.

    note the idiom
    "for variable_name in file_object"

    note that since this code reads each
    line in turn, so huge file is of no-problemo

    the code is based from Python
    Cookbook of Alex Martelli & David
    Ascher, page 121

    in Python terminal, type help() then
    'FILES' and or 'sys'
    for reference.

    try to modify this file for your
    In perl, similar code can be achieved.
    the following code illustrates.

    if (scalar @ARGV != 4) {die "Wrong arg! Unix BNF: $0 <sstr> <rstr>
    <file id1> <file id2>\n"}
    $infile = $ARGV[2];
    $outfile = $ARGV[3];
    open(F1, "<$infile") or die "Perl fucked up. Reason: $!";
    open(F2, ">$outfile") or die "Perl fucked up. Reason: $!";
    while ($line = <F1>) {
    $line =~ s/$stext/$rtext/g;
    print F2 "$line\n";
    close(F1) or die "Perl fucked up. Reason: $!";
    close(F2) or die "Perl fucked up. Reason: $!";

    Xah Lee, Jan 26, 2005
    1. Advertisements

  2. Xah Lee

    Haibao Tang Guest

    OK. But please don't die throwing that string, or this post will lose
    its educational purpose as it was meant to be.
    Haibao Tang, Jan 26, 2005
    1. Advertisements

  3. Xah Lee

    takarov2003 Guest

    I guess there is no way to check if the file opened fine? What if the
    filesystem or file is locked for this user/session. Pretty puny
    language if it cannot tell you that it cannot do what you tell it to.
    Same for the close. Is there no way check a good close?

    In 7 years of perl programming, I have never seen an open error that
    had anything to do with perl processing. Normally, if I get an error,
    the file does not exist, or has permissions set so that the current
    user/session is not allowed to open the file.
    Same here. Never seen Perl **** up on closing a file. Usually
    something in the OS or file system that does it.
    takarov2003, Jan 26, 2005
  4. Xah Lee

    Dan Perl Guest

    An exception (IOError) is raised when a file operation fails. The open()
    and and close() statements should be enclosed in a try-except statement.

    Please, take Xah Lee's postings with more than just a grain of salt. As a
    matter of fact, you are better off ignoring them than trying to learn from
    them. He is an egomaniac who is learning python and who thinks that he can
    already teach others. Personally I doubt he will ever learn python well
    enough to teach others. Just look at his English. He has a similar list
    with a-word-a-day just like the perl-python a-lesson-a-day and he seems
    indeed to know a lot of words. But his grammar is horrendous (there's a
    word for you, Xah Lee!). And according to his own website he's been living
    in North America for more than 15 years! English is a second language for
    me too but you won't see me writing something like "this groups is for
    Perlers who wants to learn Python".

    It may be unfair to pick on his English, but it is the best way I can make
    the point to someone who does not know python that Xah Lee does not know
    what he's talking about. I find Xah Lee annoying and I could just ignore
    him, but I am concerned that some people may actually take his statements
    seriously and learn from them. I can't imagine why or how, but there are
    actually 26 members in the perl-python Yahoo! group who have registered to
    get these bogus lessons sent to them daily!

    Dan Perl, Jan 26, 2005
  5. Xah Lee

    Ala Qumsieh Guest

    In this case, I'm pretty sure it's the user.

    Ala Qumsieh, Jan 26, 2005
  6. Xah Lee wrote:
    Why scalar()? The comparison already creates a scalar context, no need to
    enforce it twice.
    Ouch, how ugly. What's wrong with a simple
    my ($one, $two, $three, $four) = @ARGV;

    or the standard way using shift
    for ($one, $two, $three, $four) {
    $_ = shift;
    Really? Usually it's either the OS or the user (disk full, no write
    permissions, wrong file name, ...)
    Why $line? It doesn't serve any useful purpose here.
    Why chomp()? It doesn't serve any useful purpose here.
    If you would not have used $line above then you would not need the binding
    If you would not have chomped the line above then you would not need to add
    the newline back here. A simpler
    print F2 $_;
    would have sufficed
    I find this highly unlikely. If at all then the OS failed to complete the

    Jürgen Exner, Jan 26, 2005
  7. To follow up on Jurgen Exner's critique, I present Xah Lee's version, and
    then my rewritten version.

    use warnings;
    use strict;

    if (@ARGV != 4) {
    die "Wrong arg! Unix BNF: $0 <sstr> <rstr> <file id1> <file id2>"
    my ($stext, $rtext, $infile, $outfile) = @ARGV;

    open my $infh, '<', $infile
    or die "Error opening input file [$infile]: $!";
    open my $outfh, '>', $outfile
    or die "Error opening output file [$outfile]: $!";

    while(<$infh>) {
    print { $outfh } $_;
    close($infh) or die "Error closing input file [$infile]: $!";
    close($outfh) or die "Error closing output file [$outfile]: $!";

    My version takes up more lines, but I don't count whitespace--
    whitespace is not expensive, and when used properly adds greatly to
    the readability of your program.

    I've set followups to the only appropriate group for Mr. Lee's

    Eric Schwartz, Jan 27, 2005
  8. [ Followup set ]

    There is one born every minute.
    Tad McClellan, Jan 27, 2005
  9. Xah Lee

    kosh Guest

    Nah it is daily humor. Just think of it like a joke list. :)
    kosh, Jan 27, 2005
  10. Xah Lee

    alex23 Guest

    Or a daily puzzler: how many blatantly stupid things can you find in 5
    alex23, Jan 27, 2005
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.