fixes from mmarchini

INSTALL.md

@@ -58,8 +58,7 @@ To test that the build works, you can try running the test suite, and a one-line
 The llvm/clang packages that are currently available for Ubuntu have an issue, so we'll use the ones from llvm.org for now. The build instructions are:
 
 ```
-vi /etc/apt/sources.list
----append---
+cat <<EOF | sudo tee -a /etc/apt/sources.list
 # from https://apt.llvm.org/:
 deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial main
 deb-src http://apt.llvm.org/xenial/ llvm-toolchain-xenial main
@@ -69,10 +68,10 @@ deb-src http://apt.llvm.org/xenial/ llvm-toolchain-xenial-5.0 main
 # 6.0
 deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-6.0 main
 deb-src http://apt.llvm.org/xenial/ llvm-toolchain-xenial-6.0 main
----append---
-apt-get update
-apt-get install -y bison cmake flex g++ git libelf-dev zlib1g-dev libfl-dev
-apt-get install clang-5.0 libclang-5.0-dev libclang-common-5.0-dev libclang1-5.0 libllvm5.0 llvm-5.0 llvm-5.0-dev llvm-5.0-runtime
+EOF
+sudo apt-get update
+sudo apt-get install -y bison cmake flex g++ git libelf-dev zlib1g-dev libfl-dev
+sudo apt-get install clang-5.0 libclang-5.0-dev libclang-common-5.0-dev libclang1-5.0 libllvm5.0 llvm-5.0 llvm-5.0-dev llvm-5.0-runtime
 git clone https://github.com/iovisor/bpftrace
 cd bpftrace
 mkdir build; cd build; cmake -DCMAKE_BUILD_TYPE=DEBUG ..

docs/reference_guide.md

@@ -387,8 +387,8 @@ Attaching 1 probe...
 Syntax:
 
 ```
-profile:hz:rate
-profile:s:rate
+interval:hz:rate
+interval:s:rate
 ```
 
 This fires on one CPU only, and can be used for generating per-interval output.
@@ -926,6 +926,31 @@ Attaching 2 probes...
 
 # Map Functions
 
+Maps are special BPF data types that can be used to store counts, statistics, and histograms. They are also used for some variable types as discussed in the previous section, whenever `@` is used: [globals](#21-global), [per thread variables](#22-per-thread), and [associative arrays](#3--associative-arrays).
+
+When bpftrace exits, all maps are printed. For example (the `count()` function is covered in the sections that follow):
+
+```
+# bpftrace -e 'kprobe:vfs_read { @[comm] = count(); }'
+Attaching 1 probe...
+^C
+
+@[systemd]: 6
+@[vi]: 7
+@[sshd]: 16
+@[snmpd]: 321
+@[snmp-pass]: 374
+```
+
+The map was printed after the Ctrl-C to end the program. If you use maps that you do not wish to be automatically printed on exit, you can add an END block that clears the maps. For example:
+
+```
+END
+{
+	clear(@start);
+}
+```
+
 ## 1. Builtins
 
 - `count()` - Count the number of times this function is called