updated bash, added completion example

1 files changed, 35 insertions, 5 deletions

diff --git a/src/bash.md b/src/bash.md
index 1dd35a8..a4df7da 100644
--- a/src/bash.md
+++ b/src/bash.md
@@ -121,19 +121,49 @@ COMP_CWORD      # index into COMP_WORDS with current cursor position
 COMPREPLY       # array with possible completions
 ```
 
-`compgen` builtin is used to generate possible matches for `word` out of possible `option`s.
-The syntax is as follows:
+The `compgen` builtin is used to generate possible matches by comparing `word`
+against words generated by `option`.
 ```bash
 compgen [option] [word]
 
 # usefule options:
+# -W <list>    specify list of possible completions
+# -d           generate list with dirs
+# -f           generate list with files
+# -u           generate list with users
+# -e           generate list with exported variables
 
-# -W <list>    compare against word-list
+# compare "f" against words "foo" "foobar" "bar" and generate matches
 compgen -W "foo foobar bar" "f"
 
-# -d    compare against dir names
-# -f    compare against file names
+# compare "hom" against file/dir names and generate matches
 compgen -d -f "hom"
 ```
 
+### Example
+Skeleton to copy/paste for writing simple completions.
+
+Assume a program `foo` with the following interface:
+```bash
+foo -c green|red|blue -s low|high -f <file> -h
+```
+
+The completion handler could be implemented as follows:
+```bash
+function _foo() {
+    local curr=$2
+    local prev=$3
+
+    local opts="-c -s -f -h"
+    case $prev in
+        -c) COMPREPLY=( $(compgen -W "green red blue" -- $curr) );;
+        -s) COMPREPLY=( $(compgen -W "low high" -- $curr) );;
+        -f) COMPREPLY=( $(compgen -f -- $curr) );;
+        *)  COMPREPLY=( $(compgen -W "$opts" -- $curr) );;
+    esac
+}
+
+complete -F _foo foo
+```
+
 [dup2]: http://man7.org/linux/man-pages/man2/dup.2.html