mirror of
https://github.com/flokoe/bash-hackers-wiki.git
synced 2024-11-25 15:53:41 +01:00
83 lines
2.3 KiB
Markdown
83 lines
2.3 KiB
Markdown
# The caller builtin command
|
|
|
|
## Synopsis
|
|
|
|
caller [FRAMENUMBER]
|
|
|
|
## Description
|
|
|
|
The `caller` builtin command is used to print execution frames of
|
|
subroutine calls. Without giving a framenumber, the topmost execution
|
|
frame information is printed (\"who called me\") wile linenumber and
|
|
filename.
|
|
|
|
When an execution frame number is given (0 - topmost), the linenumber,
|
|
the subroutine (function) and the filename is printed. When an invalid
|
|
execution frame number is given, it exists `FALSE`. This way it can be
|
|
used in a loop (see the examples section below).
|
|
|
|
## Examples
|
|
|
|
### Simple stack trace
|
|
|
|
The code below defines a function `die` that is used to exit the
|
|
program. It prints a list of execution frames, starting with the topmost
|
|
frame (0). The topmost frame is the \"caller of the die function\", in
|
|
this case function \"f1\".
|
|
|
|
This way, you can print a \"stack trace\" for debugging or logging
|
|
purposes.
|
|
|
|
The code is made very simple, just to show the basic purposes.
|
|
|
|
``` bash
|
|
#!/bin/bash
|
|
|
|
die() {
|
|
local frame=0
|
|
while caller $frame; do
|
|
((++frame));
|
|
done
|
|
echo "$*"
|
|
exit 1
|
|
}
|
|
|
|
f1() { die "*** an error occured ***"; }
|
|
f2() { f1; }
|
|
f3() { f2; }
|
|
|
|
f3
|
|
```
|
|
|
|
**Output**
|
|
|
|
12 f1 ./callertest.sh
|
|
13 f2 ./callertest.sh
|
|
14 f3 ./callertest.sh
|
|
16 main ./callertest.sh
|
|
*** an error occured ***
|
|
|
|
## Notes
|
|
|
|
- `caller` produces no output unless used within a script that's run
|
|
from a real file. It isn't particularly useful for interactive use,
|
|
but can be used to create a decent `die` function to track down
|
|
errors in moderately complex scripts.
|
|
`{ bash /dev/stdin; } <<<$'f(){ g; }\ng(){ h; }\nh(){ while caller $((n++)); do :; done; }\nf'`
|
|
- For more sophisticated debugging, Bash extended debugging features
|
|
are available and a number of special parameters that give more
|
|
detail than caller (e.g. BASH_ARG{C,V}). Tools such as
|
|
[Bashdb](http://bashdb.sourceforge.net/) can assist in using some of
|
|
Bash's more advanced debug features.
|
|
- The Bash manpage and help text specifies that the argument to
|
|
`caller` is an \"expr\" (whatever that means). Only an integer is
|
|
actually allowed, with no special interpretation of an
|
|
\"expression\" as far as we can tell.
|
|
|
|
## Portability considerations
|
|
|
|
- `caller` is not specified by POSIX(R)
|
|
- the `caller` builtin command appeared in Bash version 3.0
|
|
|
|
## See also
|