Trap all commands in function

Question

I'm working with a set of scripts with functions treated as readonly. The functions are more than just a list of commands, for example, there can be loops and change directories and even calls to other functions:

func() {
    cd folder/
    run command1
    mkdir folder2/ ; cd folder2/
    run command2
}

For a moment, pretending that I could change the scripts, to show you what I want one might look like this:

func() {
    cd folder/
    string[0]="command1" ; run command1 |& tee out0.log ; result[0]="$?" ; finished_command_number 0
    mkdir folder2/ ; cd folder2/
    string[1]="command2" ; run command2 |& tee out1.log ; result[1]="$?" ; finished_command_number 1
}

So, for commands which can be piped, but not for cd or loops, I want to store a string, store the stdout (stderr), store the exit code, and run another command afterwards. However, I cannot add this in, it must be done in my script which is invoking the one with func().

To just get the post command call functionality alone, I've tried copying the function and running it from my script with a trap foo debug, but that doesn't seem to propagate into functions. I don't think literally copying line by line will work because the cd and loops can't really be isolated since they are control statements rather than subshell commands.

If the strings can just be a function of the commands themselves, that's still useful.

Answer 1

#!/bin/bash
# test.sh
post() {
        echo "post [$BASH_COMMAND] [$?]"
        echo "== $RANDOM =="
}
set -o functrace
trap post debug
func() {
        . check.sh
        tryme |& tee out.txt
}
func

The output can be filtered by the lines marked with random. I should test this further to see how well it works with multiple processes, but it seems to work just fine with short lived commands. Notice the exit code lags by one command since debug is apparently called first.

#!/bin/bash
# check.sh
tryme() {
        echo "one"
        echo "two"
        mkdir -p hello
        cd hello/
        echo "three"
        false
        echo "four"
}

===

$ bash test.sh 
post [func] [0]
== 22542 ==
post [func] [0]
== 10758 ==
post [. check.sh] [0]
== 9115 ==
post [tryme 2>&1] [0]
== 11979 ==
post [tee out.txt] [0]
== 17814 ==
post [tryme 2>&1] [0]
== 22838 ==
post [echo "one"] [0]
== 5251 ==
one
post [echo "two"] [0]
== 18036 ==
two
post [mkdir -p hello] [0]
== 4247 ==
post [cd hello/] [0]
== 21611 ==
post [echo "three"] [0]
== 24685 ==
three
post [false] [0]
== 8557 ==
post [echo "four"] [1]
== 7565 ==
four

Answer 2

If I'm reading your question correctly, you're looking for a way to:

• Capture stdout and stderr independently from the outputs of a function call
• Preserve the current working directory against any changes to it in the course of a function's execution

This can be done rather simply:

#!/bin/bash
stdout=/path/to/output.std
stderr=/path/to/output.err

somefunc() {
    : Do things
}

( somefunc arg1 arg2 ) >> $stdout 2>> $stderr

Running the function in a subshell will allow it to do whatever it needs to with respect to changing the working directory, and outputting to both stdout and stderr as normal. When the subshell exits, the working directory of the script is unchanged, and all of the stdout and stderr outputs are caught and redirected into your log files.

Adding a (global or otherwise) array in which to capture exit codes of commands is trivial:

declare -a exitcodes
( exit 0 )
exitcodes+=( $? )
( exit 2 )
exitcodes+=( $? )
( exit 0 )
exitcodes+=( $? )

echo ${exitcodes[@]}