Why is this grep command not coming back with anything? (Bash)

Question

I have a text file 'samp' that I want to grep ONLY lines that start and end with uppercase vowels.

Using "grep ^[AEIOU] samp" works.
Using "grep [AEIOU]$ samp" works as well.

But when trying to combine them to "grep ^[AEIOU]$ samp" it returns nothing.

3 things:

• Yes, I have lines that start and end with uppercase vowels in samp.
• Yes, I tried every combination of quotes I could think of. Nothing still.
• Yes, I'm new to unix.

Any help would be appreciated.

Answer 1

Your pattern allows for exactly one vowel on the line. Try:

grep ^[AEIOU].*[AEIOU]$

Note that this will not now match lines with a single vowel, if you need that too then we need to get a bit cleverer and use some "or"s.

Answer 2

Your "combined" example is looking for lines that consist of a SINGLE uppercase vowel on a line! What you wanted is:

grep '^[AIOUE].*[AIOUE]$' samp

Answer 3

What you are giving is a grep for lines that are exactly 1 capital vowel.

Try this:

 <cmd> | grep '[AEIOU]$' | grep '^[AEIOU]'

I'm sure it can be done using one grep, but I don't know the unix grep very well. If the regex is like perl it would be

 <cmd> | grep '^[AEIOU](.*[AEIOU])?$'

Answer 4

In discussing grep, the 1st edition of Mastering Regular Expressions by Jeffrey Friedl has a "Superficial Survey of a Few Common Programs' Flavor" in Table 6-1 on page 182.

He says "even something as simple as grep varies widely"

The regular expressions in grep are NOT the same as Perl.

Even egrep with extended regular expressions is not the same, but I find it easier to use.

Answer 5

This will match a line that consists only of any number of capital vowels (this includes zero, so it matches blank lines):

grep '^[AEIOU]*$'

This matches lines that consist only of one or more capital vowels (does not match blank lines):

grep -E '^[AEIOU]+$'

Either of these will match a line that consists of only one capital vowel.

Answer 6

Using egrep you could do something like:

echo $'hello\nworld' | egrep '^h|d$'