Xtrace equivalent in the fish shell

debuggingfish

Is there an equivalent of POSIX shells' set -x or set -o xtrace that cause the shell to display the commands being run in the fish shell?

Best Answer

Since fish 3.1.0, the fish_trace variable makes this functionality available:

> set fish_trace on; isatty; set -e fish_trace
++ source share/fish/functions/isatty.fish
++++ function isatty -d 'Tests if a file descriptor is a tty'
+ isatty
+++ set -l options h/help
+++ argparse -n isatty h/help --
+++ if
+++ set -q _flag_help
+++ end if
+++ if
+++ set -q 'argv[2]'
+++ end if
+++ set -l fd
++++ set fd 0
+++ '[' -t 0 ']'
+ set -e fish_trace

The location of the trace output is controlled by the --debug-output option to the fish process.

Before fish 3.1.0, you can use fish -p some_trace_file to run a fish session which outputs a profile to "some_trace_file", which can achieve almost the same effect (with some disadvantages - see the comments below).

Related Solutions

Shell – how to reference a variable in fish shell with a default fallback

I believe you need temponary variable (or a function). If $TEST doesn't exist, it's expanded to nothing, and $test_or only contains 1. It would be nice to have real way of doing that, but currently the syntax is issue, and it doesn't appear it's really needed for most purposes.

set test_or $TEST 1
echo $test_or[1]

Also, if all you want is to modify $TEST if it doesn't exist already, you can use set -q.

set -q TEST; or set TEST 1
echo $TEST

Bash – Inline debug (xtrace) in scripts

I'm not aware of any shell that has such an operator. However, with most shells (ksh being the exception) you can silently toggle xtrace with:

{
  case $- in
    (*x*) set +x;;
    (*) set -x
  esac
} 2> /dev/null

So you could make it an alias:

alias 'xx={
  case $- in
    (*x*) set +x;;
    (*) set -x
  esac
} 2> /dev/null'

And use as:

set -x
echo traced
xx; echo not traced; xx
echo traced
set +x

Note that with bash, you need shopt -s expand_aliases for aliases to be expanded in non-interactive shells (like in scripts).

Best Answer

Related Solutions

Shell – how to reference a variable in fish shell with a default fallback

Bash – Inline debug (xtrace) in scripts

Related Question