![]() ![]() ![]() Python String replace() function syntax is: str.replace(old, new) We also open the file for RW so we do it all on the same FH at once.Python string replace() function is used to create a string by replacing some parts of another string. Here we roll our own buffer IO, but we do it manually and arbitrarily on 1024 bytes. Check perldoc -f sysread and perldoc -f syswrite for more information, essentially they skip buffered io. You can use IO::Handle's setvbuf to manage the default buffers, or you can manage your own buffers with sysread and syswrite. You will need to add a newline to the very end of the file if it has one, because the tr command will remove it. Test XJS C4JD QADn1 nSBn3 2IDnEn GTUBE STAnDARD AnTI UBE-TEST EMAIL*C.34X test Test XJS C4JD QADN1 NSBN3 2IDNEN GTUBE STANDARD ANTI UBE-TEST EMAIL*C.34X ~]# fold -w 20 -s mailtest.txtĮMAIL*C.34X ~]# fold -w 20 -s mailtest.txt | sed 's/N/n/g'ĮMAIL*C.34X ~]# fold -w 20 -s mailtest.txt | sed 's/N/n/g' | tr '\n' '\0' Here is an example broken down by each step that converts all the N's to lowercase: ~]# cat mailtest.txt Instead of 1024, you might try 102576 for the -w option of fold. You should consider trying larger block sizes to see if it performs faster. ![]() Then the tr command will "unfold" the file converting the newlines that were inserted back to nothing. The sed command is yours and does what you expect. Here, fold will grab up to 1024 bytes, but the -s makes sure it breaks on a space if there is at least one since the last break. In the example below I have chosen a "block size" of 1024 characters. For this to be robust you need to know that you have at least one space in every X characters, where X is your arbitrary "block size". Here is another single UNIX command line that might perform better than other options, because you can "hunt" for a "block size" that performs well. # memoryview object subscripts to a memoryview object # mmap object subscripts to bytes (making a copy) Mem = mmap.mmap((), 0, access=mmap.ACCESS_READ) # sys.stdout requires str, but we want to write bytes # (but it must be a regular file, to support mapping it), On the plus side, you get error-reporting for free (python "exceptions") :). In particular, care is needed to avoid copying the file in memory, which would defeat the point entirely. There are several annoying subtleties, but it does avoid having to write C code. The necessary operations are all included in Python. Virtual mappings can be useful as a simple hack in cases like this. So you don't have enough physical memory (RAM) to hold the whole file at once, but on a 64-bit system you have enough virtual address space to map the entire file. If you can pick the last character of the file as the record separator, you'll avoid any portability trouble. that it processes the last partial line without truncating it and without appending a final newline. Note that this technique assumes that sed operates seamlessly on a file that doesn't end with a newline, i.e. raw_unk>/g' |Īlternatively, use the last character. If the file may start with unk>, change the sed command to sed '2,$ s/… to avoid a spurious match. You could also anchor on the first character of the text you're searching for, assuming that it isn't repeated in the search text and it appears frequently enough. tr processes bytes, not lines, so it doesn't care about any record size. Since most tools don't allow custom record separators, swap between that character and newlines. If there's an ASCII character that appears frequently in the file and doesn't appear in or, then you can use that as the record separator. They tend to work by reading one record (one line), manipulating it, and outputting the result, then proceeding to the next record (line). The usual text processing tools are not designed to handle lines that don't fit in RAM. ![]()
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