grep for lines/files that contain exactly X chars

Question

Here's the output of a grep command I ran:

[user@localhost] : ~/Documents/challenge $ grep -i -e ".\{32\}" fileA fileB fileA:W0mMhUcRRnG8dcghE4qvk3JA9lGt8nDl fileB:observacion = new Observacion(); fileB:observacion.setCodigoOf(ordenBO.getCodigo()); fileB:observacion.setDetalle(of.getObservacion().getSolicitante()); fileB:observacion.setTipoObservacion(TipoObservacionOrdenFleteMaestro.SOLICITANTE); fileB:observacion.setProceso(TipoProcesoObservacionMaestro.MODIFICACION); fileB:observacion.setFecha(Utiles.getFechaSistema()); fileB:java.util.Date fechaHora = Calendar.getInstance().getTime(); fileB:observacion.setUsuarioCrecion(usuarioSesionado.getUsuario().getUsuario()); fileB:daoObservacion.agregaObservacion(observacion);

I'm looking for 32 character long string in two files: fileA and fileB. Importantly, fileA contains exactly 32 characters only, with no line breaks:

[user@localhost] : ~/Documents/challenge $ hexdump -C fileA 00000000 57 30 6d 4d 68 55 63 52 52 6e 47 38 64 63 67 68 |W0mMhUcRRnG8dcgh| 00000010 45 34 71 76 6b 33 4a 41 39 6c 47 74 38 6e 44 6c |E4qvk3JA9lGt8nDl| 00000020

The problem with my grep command is that it is returning any line that has more than 32 chars. How can I make it return only lines with exactly 32 chars. The issue for me is that I can't modify my regex to match on a line break, because there is no line break.

My expected output would be simply:

fileA:W0mMhUcRRnG8dcghE4qvk3JA9lGt8nDl

(note: this is for a challenge that I've already solved with my ugly solution, but in this scenario we can only use grep and piping or redirecting output is not allowed)

steve · Accepted Answer · 2015-07-14 19:15:59Z

This works. ^ denotes start of line, plus the {32} you already had, then a $ for end of line.

$ cat fileA fileB 12345678901234567890123456789012 123456789012345678901234567890123 12345678901234567890123456789012 123456789012345678901234567890124 $ grep -E "^.{32}$" fileA fileB fileA:12345678901234567890123456789012 fileB:12345678901234567890123456789012 $

And as pointed out by @steeldriver, posix grep includes -x, so the following approach also works : grep -xE ".{32}" fileA fileB

POSIX grep should also support the -x or --line-regexp whole-line match, I think — steeldriver
– steeldriver, Commented Jul 14, 2015 at 19:11

evilsoup · Accepted Answer · 2015-07-14 19:11:58Z

According to the GNU Grep documentation:

If the final byte of an input file is not a newline, grep silently supplies one.

So, if you're using GNU grep, you should be able to use the beginning-of-line/end-of-line anchors (^ and $) as usual, even if you're not working on properly-formed plaintext files.

grep '^.\{32\}$' fileA fileB

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