gistfile1

See the EC2 documentation on the subject.

Run:

wget -q -O - http://169.254.169.254/latest/meta-data/instance-id
If you need programatic access to the instance ID from within a script,

die() { status=$1; shift; echo "FATAL: $*"; exit $status; }
EC2_INSTANCE_ID="`wget -q -O - http://169.254.169.254/latest/meta-data/instance-id || die "wget instance-id has failed: $?"`"
An example of a more advanced use (retrieve instance ID as well as availability zone and region, etc.):

EC2_INSTANCE_ID="`wget -q -O - http://169.254.169.254/latest/meta-data/instance-id || die "wget instance-id has failed: $?"`"
test -n "$EC2_INSTANCE_ID" || die 'cannot obtain instance-id'
EC2_AVAIL_ZONE="`wget -q -O - http://169.254.169.254/latest/meta-data/placement/availability-zone || die "wget availability-zone has failed: $?"`"
test -n "$EC2_AVAIL_ZONE" || die 'cannot obtain availability-zone'
EC2_REGION="`echo "$EC2_AVAIL_ZONE" | sed -e 's:([0-9][0-9]*)[a-z]*$:\1:'`"
You may also use curl instead of wget, depending on what is installed on your platform.