In a bash read loop, processing ! (exclamation) and trapping CTRL-Z

Question

I am trying to extend bash with custom code that reuses bash's capability to terminate and suspend forked processes and also bash's expansion of !.

I tried a variation of the code in BASH - using trap ctrl+c that has certain lines commented out from that solution and a few lines added for trapping ctrlz:

#!/bin/bash
# type "finish" to exit

#stty -echoctl # hide ^C

# function called by trap
other_commands() {
    #printf "\rSIGINT caught      "
    #tput setaf 1
    #printf "\rSIGINT caught      "
    #tput sgr0
    #sleep 1
    #printf "\rType a command >>> "
    echo ""
}

trap 'other_commands' SIGINT
trap 'other_commands' TSTP
trap 'other_commands' SIGTSTP

#input="$@"

while true; do
    printf "\rType a command >>> "
    read input
    [[ $input == finish ]] && break
    bash -c "$input"
done

CTRL C works nicely, it kills the created process but not the bash extension.

However, CTRLZ kind of works. when I execute ls | more and then CTRLZ, it suspends the process:

dewan    1934441  0.0  0.1   9800  3144 pts/6    S+   17:00   0:00 bash ctrlc.sh
dewan    1934442  0.0  0.1   9800  3300 pts/6    T+   17:00   0:00 bash -c ls | more

But I cannot do anything in the bash extension after that:

initx11
j2h
j2h.bat
j2h.jar
j2hlink
jargipc
--More--
^Z

I read here (Shell Script get CTRL+Z with Trap) that sigstop cannot be trapped but sigtstp can (in case there is a difference), and as we see it is allowed by bash. Iwas wondering if there is a workaround. Uncommenting the lines from the original solution did not improve things.

A second issue is that I cannot use ! to reuse history commands in the bash extension. For example, !! does not execute the last command.

 jaroeold                     pt2t.sed                       uc
 jaroewithoutvt               r2b
Type a command >>> !ls
bash: !ls: command not found
Type a command >>>

The ! prefix is not expanded by bash. Is there a way to make bash expand it? I can duplicate the functionality but was curious if one can devise a solution that did not require such duplication.

Thanks, and this my first stackoverflow question I believe so pardon any mistakes in formatting and contents.

In a bash read loop, processing ! (exclamation) and trapping CTRL-Z

0 Answers0