string replace in a large file with php

Question

I am trying to do a string replace for entire file in PHP. My file is over 100MB so I have to go line by line and can not use file_get_contents(). Is there a

Answer 1

If you can't use directly sed from command line because it's a dynamic task and you need to call it from php it's difficult to get the syntax right: you must escape in different ways in the search and replacement strings these characters

' / $ . * [ ] \ ^ &

The following function search and replace a string in a file without interpreting the searched string as a regular expression. So if you wanted you could search for the string ".*" and replace it with "$".

/**
 * str_replace_with_sed($search, $replace, $file_in, $file_out=null)
 * 
 * Search for the fixed string `$search` inside the file `$file_in`
 * and replace it with `$replace`. The replace occurs in-place unless
 * `$file_out` is defined: in that case the resulting file is written
 * into `$file_out`
 *
 * Return: sed return status (0 means success, any other integer failure)
 */
function str_replace_with_sed($search, $replace, $file_in, $file_out=null)
{
    $cmd_opts = '';
    if (! $file_out) 
    {
        // replace inline in $file_in
        $cmd_opts .= ' -i';
    }

    // We will use Basic Regular Expressions (BRE). This means that in the 
    // search pattern we must escape
    // $.*[\]^
    //
    // The replacement string must have these characters escaped
    // \ & 
    //
    // In both cases we must escape the separator character too ( usually / )
    // 
    // Since we run the command trough the shell we We must escape the string
    // too (yai!). We're delimiting the string with single quotes (') and we'll
    // escape them with '\'' (close string, write a single quote, reopen string)    

    // Replace all the backslashes as first thing. If we do it in the following
    // batch replace we would end up with bogus results
    $search_pattern = str_replace('\\', '\\\\', $search);

    $search_pattern = str_replace(array('$', '.', '*', '[', ']', '^'),
                                  array('\\$', '\\.', '\\*', '\\[', '\\]', '\\^'),
                                  $search_pattern);

    $replace_string = str_replace(array('\\', '&'),
                                  array('\\\\', '\\&'),
                                  $replace);

    $output_suffix = $file_out ? " > '$file_out' " : '';
    $cmd = sprintf("sed ".$cmd_opts." -e 's/%s/%s/g' \"%s\" ".$output_suffix,
                    str_replace('/','\\/', # escape the regexp separator
                      str_replace("'", "'\''", $search_pattern) // sh string escape
                    ),
                    str_replace('/','\\/', # escape the regexp separator
                      str_replace("'", "'\''", $replace_string) // sh string escape
                    ),
                    $file_in
                  );

    passthru($cmd, $status);

    return $status;
}