Processing of text

Question

It is pleasure to ask you about something I cannot solve myself. I am working with big text files with many similar lines. The format of the files is defined and I want to replace repetitively some characters appearing in some columns of the files. For example I would like to substitute in a file similar to this below, when the last number 3.0e-4 is, from the 5th to the 7th character by aaa, in this case yyy will be substitute by aaa:

ASDEFxxx          3.0E+12ERT          SAA      1.0e-4
ASEEFyyy          4.0E+12EDT          ABA      3.0e-4
ASAEFzzz          5.0E+12ERF          ADA      2.0e-4

In this example I would like to use replace regexp to replace in this case only the second line. The result should be:

ASDEFxxx          3.0E+12ERT          SAA      1.0e-4
ASEEFaaa          4.0E+12EDT          ABA      3.0e-4
ASAEFzzz          5.0E+12ERF          ADA      2.0e-4

There are many lines in the file to be substituted...

Does anybody write the command with replace regexp to do that?

Thanks and regards, Manuel

Answer 1

C-x h C-M-% \(.\{5\}\).\{3\}\(.*3.0e-4\) RET \1aaa\2 RET

Dissection:

• C-x h select the whole file
• C-M-% run query-replace-regexp (you may want M-x replace-regexp instead)
• \(.\{5\}\) capture 5 characters into the group \1.
• .\{3\} match three characters (will discard)
• \(.*3.0e-4\) match the rest of the line, ensuring 3.0e-4 and capture in \2