From f81b1f23a526450e16992e2e248495365d9e394d Mon Sep 17 00:00:00 2001
From: johannst <johannes.stoelp@gmail.com>
Date: Sat, 11 Apr 2020 19:28:57 +0200
Subject: bash add expansion + completion notes

---
 src/bash.md | 91 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 89 insertions(+), 2 deletions(-)

(limited to 'src')

diff --git a/src/bash.md b/src/bash.md
index 0028724..1dd35a8 100644
--- a/src/bash.md
+++ b/src/bash.md
@@ -17,10 +17,59 @@
 ### Parameter
 ```bash
 # default param
-# if $foo set, then bar=$foo else bar=some_val
-bar=${foo:-some_val}
+bar=${foo:-some_val}  # if $foo set, then bar=$foo else bar=some_val
+
+# check param set
+bar=${foo:?msg}  # if $foo set, then bar=$foo else exit and print msg
+
+# indirect
+FOO=foo
+BAR=FOO
+bar=${!BAR}  # deref value of BAR -> bar=$FOO
+
+# prefix
+${foo#prefix}  # remove prefix when expanding $foo
+# suffix
+${foo%suffix}  # remove suffix when expanding $foo
+
+# substitute
+${foo/pattern/string}  # replace pattern with string when expanding foo
+# pattern starts with
+# '/'   replace all occurences of pattern
+# '#'   pattern match at beginning
+# '%'   pattern match at end
+```
+
+> Note: `prefix`/`suffix`/`pattern` are expanded as [pathnames](#pathname).
+
+### Pathname
+
+```bash
+*           match any string
+?           match any single char
+\\          match backslash
+[abc]       match any char of 'a' 'b' 'c'
+[a-z]       match any char between 'a' - 'z'
+[^ab]       negate, match all not 'a' 'b'
+[:class:]   match any char in class, available:
+              alnum,alpha,ascii,blank,cntrl,digit,graph,lower,
+              print,punct,space,upper,word,xdigit
 ```
 
+Wit `extglob` shell option enabled it is possible to have more powerful
+patterns. In the following `pattern-list` is one ore more patterns separated
+by `|` char.
+
+```bash
+?(pattern-list)   matches zero or one occurrence of the given patterns
+*(pattern-list)   matches zero or more occurrences of the given patterns
++(pattern-list)   matches one or more occurrences of the given patterns
+@(pattern-list)   matches one of the given patterns
+!(pattern-list)   matches anything except one of the given patterns
+```
+> Note: `shopt -s extglob`/`shopt -u extglob` to enable/disable `extglob`
+> option.
+
 ## I/O redirection
 
 > Note: The trick with bash I/O redirection is to interpret from left-to-right.
@@ -49,4 +98,42 @@ command 2>&1 >file
 1. duplicate `fd 1` to `fd 2`, effectively redirecting `stderr` to `stdout`
 2. redirect `stdout` to `file`
 
+## Completion
+
+The `complete` builtin is used to interact with the completion system.
+```bash
+complete                    # print currently installed completion handler
+complete -F <func> <cmd>    # install <func> as completion handler for <cmd>
+complete -r <cmd>           # uninstall completion handler for <cmd>
+```
+
+Variables available in completion functions:
+```bash
+# in
+$1              # <cmd>
+$2              # current word
+$3              # privous word
+
+COMP_WORDS      # array with current command line words
+COMP_CWORD      # index into COMP_WORDS with current cursor position
+
+# out
+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:
+```bash
+compgen [option] [word]
+
+# usefule options:
+
+# -W <list>    compare against word-list
+compgen -W "foo foobar bar" "f"
+
+# -d    compare against dir names
+# -f    compare against file names
+compgen -d -f "hom"
+```
+
 [dup2]: http://man7.org/linux/man-pages/man2/dup.2.html
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