/usr/share/zsh/5.5.1/help
Edit: /usr/share/zsh/5.5.1/help/trap (3704B)
trap [ arg ] [ sig ... ]
arg is a series of commands (usually quoted to protect it from
immediate evaluation by the shell) to be read and executed when
the shell receives any of the signals specified by one or more
sig args. Each sig can be given as a number, or as the name of
a signal either with or without the string SIG in front (e.g. 1,
HUP, and SIGHUP are all the same signal).
If arg is `-', then the specified signals are reset to their
defaults, or, if no sig args are present, all traps are reset.
If arg is an empty string, then the specified signals are
ignored by the shell (and by the commands it invokes).
If arg is omitted but one or more sig args are provided (i.e.
the first argument is a valid signal number or name), the effect
is the same as if arg had been specified as `-'.
The trap command with no arguments prints a list of commands
associated with each signal.
If sig is ZERR then arg will be executed after each command with
a nonzero exit status. ERR is an alias for ZERR on systems that
have no SIGERR signal (this is the usual case).
If sig is DEBUG then arg will be executed before each command if
the option DEBUG_BEFORE_CMD is set (as it is by default), else
after each command. Here, a `command' is what is described as a
`sublist' in the shell grammar, see the section SIMPLE COMMANDS
& PIPELINES in zshmisc(1). If DEBUG_BEFORE_CMD is set various
additional features are available. First, it is possible to
skip the next command by setting the option ERR_EXIT; see the
description of the ERR_EXIT option in zshoptions(1). Also, the
shell parameter ZSH_DEBUG_CMD is set to the string corresponding
to the command to be executed following the trap. Note that
this string is reconstructed from the internal format and may
not be formatted the same way as the original text. The parame-
ter is unset after the trap is executed.
If sig is 0 or EXIT and the trap statement is executed inside
the body of a function, then the command arg is executed after
the function completes. The value of $? at the start of execu-
tion is the exit status of the shell or the return status of the
function exiting. If sig is 0 or EXIT and the trap statement is
not executed inside the body of a function, then the command arg
is executed when the shell terminates; the trap runs before any
zshexit hook functions.
ZERR, DEBUG, and EXIT traps are not executed inside other traps.
ZERR and DEBUG traps are kept within subshells, while other
traps are reset.
Note that traps defined with the trap builtin are slightly dif-
ferent from those defined as `TRAPNAL () { ... }', as the latter
have their own function environment (line numbers, local vari-
ables, etc.) while the former use the environment of the command
in which they were called. For example,
trap 'print $LINENO' DEBUG
will print the line number of a command executed after it has
run, while
TRAPDEBUG() { print $LINENO; }
will always print the number zero.
Alternative signal names are allowed as described under kill
above. Defining a trap under either name causes any trap under
an alternative name to be removed. However, it is recommended
that for consistency users stick exclusively to one name or
another.