5.2. I'm using 'p' to print, but I have duplicate lines sometimes.
Sed prints the entire file by default, so the 'p' command might
cause the duplicate lines. If you want the whole file printed,
try removing the 'p' from commands like 's/foo/bar/p'. If you want
part of the file printed, run your sed script with -n flag to
suppress normal output, and rewrite the script to get all output
from the 'p' comand.
If you're still getting duplicate lines, you are probably finding
several matches for the same line. Suppose you want to print lines
with the words "Peter" or "James" or "John", but not the same line
twice. The following command will fail:
sed -n '/Peter/p; /James/p; /John/p' files
Since all 3 commands of the script are executed for each line,
you'll get extra lines. A better way is to use the 'd' (delete) or
'b' (branch) commands, like so (with GNU sed):
sed '/Peter/b; /James/b; /John/b; d' files # one way
sed -n '/Peter/{p;d;};/James/{p;d;};/John/p' files # a 2nd way
sed -n '/Peter/{p;b;};/James/{p;b;};/John/p' files # a 3rd way
sed '/Peter\|James\|John/!d' files # shortest way
On standard seds, these must be broken down with -e commands:
sed -e '/Peter/b' -e '/James/b' -e '/John/b' -e d files
sed -n -e '/Peter/{p;d;}' -e '/James/{p;d;}' -e '/John/p' files
The 3rd line would require too many -e commands to fit on one line,
since standard versions of sed require an -e command after each 'b'
and also after each closing brace '}'.
