fix various bash snippets

src/profiling/with_perf.md

@@ -27,8 +27,8 @@ of events, though, like cache misses and so forth.
 
 The basic `perf` command is this:
 
-```
-perf record -F99 --call-graph dwarf XXX
+```bash
+> perf record -F99 --call-graph dwarf XXX
 ```
 
 The `-F99` tells perf to sample at 99 Hz, which avoids generating too
@@ -38,8 +38,8 @@ activity). The `--call-graph dwarf` tells perf to get call-graph
 information from debuginfo, which is accurate. The `XXX` is the
 command you want to profile. So, for example, you might do:
 
-```
-perf record -F99 --call-graph dwarf cargo +<toolchain> rustc
+```bash
+> perf record -F99 --call-graph dwarf cargo +<toolchain> rustc
 ```
 
 to run `cargo` -- here `<toolchain>` should be the name of the toolchain
@@ -74,9 +74,9 @@ do profiling for you! You can find
 
 For example, to measure the clap-rs test, you might do:
 
-```
-> ./target/release/collector \
-    --output-repo /path/to/place/output \
+```bash
+> ./target/release/collector
+    --output-repo /path/to/place/output
     profile perf-record
     --rustc /path/to/rustc/executable/from/your/build/directory
     --cargo `which cargo`
@@ -179,8 +179,8 @@ would analyze NLL performance.
 
 You can install perf-focus using `cargo install`:
 
-```
-cargo install perf-focus
+```bash
+> cargo install perf-focus
 ```
 
 ### Example: How much time is spent in MIR borrowck?