How to know if `script` command (which records terminal sessions as typescript) is already runing?

Question

This SO answer says that script adds the variable SCRIPT to the environment of the command it runs. I tried that but it doesn't seem to be working now.

This is what I have tried

ma08@IWeighHar:~/pro$ script foo.log
Script started, output log file is 'foo.log'.
ma08@IWeighHar:~/pro$ echo $SCRIPT

ma08@IWeighHar:~/pro$ exit
exit
Script done.
ma08@IWeighHar:~/pro$ echo $SCRIPT

ma07@IWeighHar:~/pro$ 

How to detect if the script command is already running in the current terminal session?

Due to the name of this command, googling regarding it is kind of a nightmare.

Answer 1

As a heuristic, you could check whether there's a process whose name is script has your terminal device opened:

if lsof -watc script "$(tty)" > /dev/null 2>&1; then
  echo I may very well be within a script session
fi

tty returns the path of the terminal opened on stdin. Some shells set the $TTY variable to the path of their controlling terminal. See also $(ps -o tty= -p "$$") to get the controlling terminal without the /dev/ prefix.

Answer 2

Since the variant or version of the script utility you use does not set the SCRIPT environment variable within the shell it starts, you can do so yourself. In variants of the utility that sets this variable, it is set to the name of the output file. The following is a short bash shell function that would mimic that behaviour:

script () {
    local outfile="${1:-typescript}"
    SCRIPT=$outfile command script "$outfile"
}

This function takes an optional single argument which is the pathname of the output typescript file. If no argument is supplied (or it's empty), the name typescript is used as the output file. The name of the output file is also available as "$SCRIPT" in the shell that the utility starts.

You would use this function like

script myfile

or as

script

Alternatively, to allow an arbitrary command at the end of the command line (requires that the first argument is the typescript output file and, just like with the above variation, does not allow for giving options to the real script command):

script () {
    local outfile="${1:-typescript}"
    shift
    SCRIPT=$outfile command script "$outfile" "$@"
}

You could use this as above, but you could also add a command to run:

script outfile mail -s testmail user@remote.host

Answer 3

This will offer what you need:

#!/bin/sh

# placing into Creative Commons - may not be claimed for copyright by any other individual or corporation.
# free to use and replicate

BASE=`basename "${0}" ".sh" `
TMP="/tmp/tmp.$$.${BASE}"

if [ $# -ne 1 ] ; then  echo "\n Must provide current shell PID by referencing it with $$ on the command line.\n" ; exit 1 ; fi

MySHELL=$1

ps -ef >${TMP}.ps
### FORMAT
#username   37539    4819  0 15:47 pts/3    00:00:00 bash
#username   37572   37539  0 15:49 pts/3    00:00:00 script scriptLog.txt
#username   37573   37572  0 15:49 pts/4    00:00:00 bash -i

awk -v sPID="${MySHELL}" '{
    if( $2 == sPID ){
        print $3 ;
    } ;
}' <${TMP}.ps |
{   read sPPID
    awk -v sPPID="${sPPID}" '{
        if( $2 == sPPID ){
            n=index( $0, "script " ) ;
            if( n == 0 ){
                print "\t safe to use \"script\"." ; exit 0 ;
            }else{
                COMMAND=substr( $0, n ) ;
                printf("BUSY [%s]:  %s\n", sPPID, COMMAND ) ; exit 1 ;
            } ; 
        } ;
    }' <${TMP}.ps
}

exit 0
exit 0
exit 0

If script is already logging the current shell, it will return RC=1 and report like this:

BUSY [37572]:  script scriptLog.txt

Otherwise, RC=0 and will report like this:

        safe to use "script".