When our server comes up we need to check a file to see how the server is configured.
We want to search for the following string inside our /etc/aws/hosts.conf file:
MYSQL_ROLE=master
Then, we want to test whether that string exists and use an if/else statement to run one of two options depending on whether the string exists or not.
What is the BASH syntax for the if statement?
if [ ????? ]; then
#do one thing
else
#do another thing
fi
This question is related to
bash
just use bash
while read -r line
do
case "$line" in
*MYSQL_ROLE=master*)
echo "do your stuff";;
*) echo "doesn't exist";;
esac
done <"/etc/aws/hosts.conf"
Note that, for PIPE
being any command or sequence of commands, then:
if PIPE ; then
# do one thing if PIPE returned with zero status ($?=0)
else
# do another thing if PIPE returned with non-zero status ($?!=0), e.g. error
fi
For the record, [ expr ]
is a shell builtin† shorthand for test expr
.
Since grep
returns with status 0 in case of a match, and non-zero status in case of no matches, you can use:
if grep -lq '^MYSQL_ROLE=master' ; then
# do one thing
else
# do another thing
fi
Note the use of -l
which only cares about the file having at least one match (so that grep
returns as soon as it finds one match, without needlessly continuing to parse the input file.)
†on some platforms [ expr ]
is not a builtin, but an actual executable /bin/[
(whose last argument will be ]
), which is why [ expr ]
should contain blanks around the square brackets, and why it must be followed by one of the command list separators (;
, &&
, ||
, |
, &
, newline)
if
takes a command and checks its return value. [
is just a command.
if grep -q ...
then
....
else
....
fi
Source: Stackoverflow.com