zsh,bash: trap handling

1 files changed, 34 insertions, 0 deletions

diff --git a/src/shells/bash.md b/src/shells/bash.md
index f27b3a2..fb511b8 100644
--- a/src/shells/bash.md
+++ b/src/shells/bash.md
@@ -133,6 +133,40 @@ v=abc ; ( v=foo; echo $v; ) ; echo $v
 # abc
 ```
 
+## Trap Handling
+
+```bash
+trap "<CMDs>" <SIG>/EXIT
+
+# Show current trap handler.
+trap -p
+# List signal names.
+trap -l
+```
+
+#### Example: Run handler only on error exit
+```bash
+trap 'test $? -ne 0 && echo "run exit trap"' EXIT
+
+# -> no print
+exit 0
+# -> print
+exit 1
+```
+
+#### Example: Mutex in shell script
+For example if a script is triggered in unsynchronized, we may want to ensure
+that a single script instance runs.
+```bash
+# open file=LOCK with fd=100
+exec 100>LOCK
+# take exclusive lock, wait maximal for 3600s
+flock -w 3600 -x 100 || { echo "flock timeout"; exit 1; }
+
+# eg automatically release lock when script exits
+trap "flock -u 100" EXIT
+```
+
 ## Argument parsing with `getopts`
 
 The `getopts` builtin uses following global variables: