sed

Daryl Lim · #1 (**permalink**) 06-18-04, 08:50

Hi

does anyone know what does the sed command do:

sed "s/[A-Z]/&/g" file

i tried running but there is no effect on the uppercase letters in the file. Is the amperstand a metacharacter in sed?

Damian Ibbotson · #2 (**permalink**) 06-18-04, 09:19

This isn't going to do anything that you would notice!

'&' in a substitution represents the pattern that was matched, so you are replacing your character A-Z, with that same character.

Try...

sed "s/[A-Z]/&&/g" file

...and you will see each character repeated because you are replacing the matched pattern with 'twice' the matched pattern.

vgersh99 · #3 (**permalink**) 06-18-04, 09:19

Quote:

Originally Posted by Daryl Lim

Hi

does anyone know what does the sed command do:

sed "s/[A-Z]/&/g" file

i tried running but there is no effect on the uppercase letters in the file. Is the amperstand a metacharacter in sed?

this sed does not change anything.
'&' back-references the matched string.

doing 'man sed' yields:

Quote:

An ampersand (&) appearing in the replacement
will be replaced by the string matching the
RE. The special meaning of & in this context
can be suppressed by preceding it by
backslash. The characters \n, where n is a
digit, will be replaced by the text matched by
the corresponding backreference expression.
For each backslash (\) encountered in scanning
replacement from beginning to end, the follow-
ing character loses its special meaning (if
any). It is unspecified what special meaning
is given to any character other than &, \ or
digits.

Daryl Lim · #4 (**permalink**) 06-18-04, 21:48

what about this command below:

sed "10r text" file

thanks
daryl

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