I want to trap signal SIGTSTP, as simple as this:
trap "" SIGTSTP
However, pure shell (sh) does not support signal name, so a trap must use the signal number instead, like this:
trap "" 20
Problem: signal numbers are OS-dependent, so SIGTSTP in Linux is 20 but in AIX it's 18.
So to make it generic I decide to extract signal number from the result of trap -l. The raw input is:
1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL
5) SIGTRAP 6) SIGABRT 7) SIGEMT 8) SIGFPE
9) SIGKILL 10) SIGBUS 11) SIGSEGV 12) SIGSYS
13) SIGPIPE 14) SIGALRM 15) SIGTERM 16) SIGURG
17) SIGSTOP 18) SIGTSTP 19) SIGCONT 20) SIGCHLD
21) SIGTTIN 22) SIGTTOU 23) SIGIO 24) SIGXCPU
25) SIGXFSZ 27) SIGMSG 28) SIGWINCH 29) SIGPWR
30) SIGUSR1 31) SIGUSR2 32) SIGPROF 33) SIGDANGER
34) SIGVTALRM 35) SIGMIGRATE 36) SIGPRE 37) SIGVIRT
38) SIGALRM1 39) SIGWAITING 50) SIGRTMIN 51) SIGRTMIN+1
52) SIGRTMIN+2 53) SIGRTMIN+3 54) SIGRTMAX-3 55) SIGRTMAX-2
56) SIGRTMAX-1 57) SIGRTMAX 60) SIGKAP 61) SIGRETRACT
62) SIGSOUND 63) SIGSAK
I can't use grep, because the feature that I need, --only-matching, is not always supported. trap -l | grep -oE "[0-9]+\) SIGTSTP" | cut -d')' -f1 works well, but only in Linux.
I also failed to use sed because of the greedy problem described here
So trap -l | sed -nr 's/.*([0-9]+)\) SIGTSTP.*/\1/p' only returns 8, not 18
I want to make the extraction as generic as possible, so I won't assume SIGTSTP is a double-digit code, even when in reality it is.
Any suggestion?
Try constraining the match with a word boundary:
trap -l | sed -nr 's/.*\b([0-9]+)\) SIGTSTP.*/\1/p'
This tested correctly [for me] for the target string as well as SIGPIPE.