CODEWITHSUNDEEP
bash
Craig
Craig

Reputation: 4399

Exporting BASH_XTRACEFD has no effect on subprocesses and it loses its special meaning

I have just noticed that exporting this converts it into an ordinary variable with no special meaning in subshells. Is this a security feature of bash?

Upvotes: 4

Views: 1224

Answers (1)

Edouard Thiel
Edouard Thiel

Reputation: 6228

This is a snippet to check the feature:

#! /bin/bash

exec 3>| trace.txt

BASH_XTRACEFD=3
set -x

# Something to trace
i=1 ; test "$i" -gt 2

# Now in a subshell
(i=2 ; test "$i" -gt 2)

# Let's export it
export BASH_XTRACEFD

# Again check trace
i=3 ; test "$i" -gt 2

# Now in a subshell
(i=4 ; test "$i" -gt 2)

And here is trace.txt:

+ i=1
+ test 1 -gt 2
+ i=2
+ test 2 -gt 2
+ export BASH_XTRACEFD
+ i=3
+ test 3 -gt 2
+ i=4
+ test 4 -gt 2

It works! May be we have different bash version. Mine is 4.3.11(1)-release (x86_64-pc-linux-gnu). What's yours?

Upvotes: 2

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