I wrote the following command in order to match $a with $b, but when the value includes "-", then I get an error. How can I avoid that?
# a="-Xmx5324m"
# b="-Xmx5324m"
#
#
# echo "$a" | grep -Fxc "$b"
grep: conflicting matchers specified
2 Answers
Place -- before your pattern:
echo "$a" | grep -Fxc -- "$b"
-- specifies end of command options for many commands/shell built-ins, after which the remaining arguments are treated as positional arguments.
Besides of @sebasth's great answer, you could tell that PATTERN with grep's -e option to use PATTERN as a pattern (here using the <<< zsh here-string operator instead of echo; see also printf '%s\n' "$a" for portability).
grep -Fxc -e "$b" <<<"$a"
Or all beside of other options.
grep -Fxce "$b" <<<"$a"
Since your goal is byte-to-byte string equality comparison use the [ command instead.
if [ "$a" = "$b" ]
Or if $a contains $b, using the [[...]] ksh construct:
if [[ $a == *"$b"* ]]
Or more portably in all Bourne-like shells:
case $a in
*"$b"*) ...
esac
-
==is not standard for the[command; it's a bashism. Use=instead.– WildcardAug 28, 2017 at 21:50
grep -Fxc -- "$b" <<< "$a"to avoid the unnecessary pipe[[ ... ]]orcasewould be a better choice, since you avoid both the idiosyncrasies ofechoand the child processes.grepas a literal character rather than the start of an option, i.e.echo test-test | grep "\-test"will match rather than complain about an unknown-tflag.