UNIX for Dummies Questions & Answers

TIT
TAT
RATA
ERAT
RATE
HI
RE
CA
PA
CHANGE
SANDY
ANSWER

cat hello|grep [A-Z]\{3,4\}

{ while read line ; do [[ "${#line}" = [34] ]] && echo "$line" ; done } <toto

#!/usr/bin/env bash

# @(#) s1	Demonstrate regex, classes, repetition, boundaries.

# Section 1, setup, pre-solution.
# Infrastructure details, environment, commands for forum posts. 
# Uncomment export command to test script as external user.
# export PATH="/usr/local/bin:/usr/bin:/bin"
set +o nounset
pe() { for i;do printf "%s" "$i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
C=$HOME/bin/context && [ -f $C ] && . $C specimen grep
set -o nounset
pe

FILE=${1-data1}

# Section 2, display input file.
# Display sample of data file, with head & tail as a last resort.
pe " || start [ first:middle:last ]"
specimen 6 $FILE \
|| { pe "(head/tail)"; head -n 5 $FILE; pe " ||"; tail -n 5 $FILE; }
pe " || end"

# Section 3, solution.
pl " Results:"
grep '^[[:upper:]]\{3,4\}$' $FILE

exit 0

% ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution        : Debian GNU/Linux 5.0 
GNU bash 3.2.39
specimen (local) 1.17
GNU grep 2.5.3

 || start [ first:middle:last ]
Whole: 6:0:6 of 12 lines in file "data1"
TIT
TAT
RATA
ERAT
RATE
HI
RE
CA
PA
CHANGE
SANDY
ANSWER
 || end

-----
 Results:
TIT
TAT
RATA
ERAT
RATE

grep -E '^[A-Z]{3}[A-Z]?$' myt

[ctsgnb@shell ~]$ cat myt
TIT
TAT
RATA
ERAT
RATE
HI
RE
CA
PA
CHANGE
SANDY
ANSWER
[ctsgnb@shell ~]$ grep -E '^[A-Z][A-Z][A-Z][A-Z]?$' myt
TIT
TAT
RATA
ERAT
RATE
[ctsgnb@shell ~]$ grep -E '^[A-Z]{3}[A-Z]?$' myt
TIT
TAT
RATA
ERAT
RATE
[ctsgnb@shell ~]$

$ ruby -ne 'print if [3,4].include?($_.scan(/[A-Z]+/)[0].size)' file

$ ruby -ne 'print if [3,4].include?($_.scan(/^[A-Z]+$/)[0].size) rescue 1' file