8 ms·

Yes, the critizised code is definitely bad. Glues two user-defined constructs together (is-in-list and a variable). Also, unquoted variables and relying on shel

Yes, the critizised code is definitely bad. Glues two user-defined constructs together (is-in-list and a variable). Also, unquoted variables and relying on shell splitting... But you don't necessarily need to shell out to awk / perl / grep / whatever. is_in_list() { local thing=$1 shift while [ $# -gt 0 ] ; do [ "$1" = "$thing" ] && return 0 shift done return 1 } Now just do `is_in_list "$thing" "$@"` where the positional array `"$@"` is the list (or by all means use unquoted `$COMPILER_VERSIONS`, i.e. unsafe shell-splitting). Another possibility, where the list is given as a space-separated string, is with case statements. That approach is logically equivalent to the awk version, but doesn't fork so is much more performant. is_in_list() { case $2 in $1|*" $1 "*|*" $1"|"$1 "*) return 0;; *) return 1;; esac } Not tested, but that's the idea.

falsedan 10y ago
Bash is all about shelling out: it's a shell. I would happily use grep here, and if I had an array: printf "%s\0" "$@" | grep -qz needle > much more performant I believe that performance-critical code shouldn't be written in bash. I have seen pipelines be much faster than tweaked bash functions, simply because they run in parallel & thus the cost of forking is paid once, up-front.
- jstimpfle 10y ago
  I agree with you. I think we are just speaking about different things. I was more thinking about the things that happen in a configure script, for example. Not a "hoot loop" like a big grep over millions of lines or something. There are situations in shell code where the difference between a case-match or string-suffix-replace written in shell and a process spawn matters. Not only because forking a process for one simple string operation is wasteful (cost: about 1ms), but also because of the semantic problems that come with child processes (error handling).

falsedan 10y ago

Bash is all about shelling out: it's a shell. I would happily use grep here, and if I had an array: printf "%s\0" "$@" | grep -qz needle > much more performant I believe that performance-critical code shouldn't be written in bash. I have seen pipelines be much faster than tweaked bash functions, simply because they run in parallel & thus the cost of forking is paid once, up-front.

jstimpfle 10y ago
I agree with you. I think we are just speaking about different things. I was more thinking about the things that happen in a configure script, for example. Not a "hoot loop" like a big grep over millions of lines or something. There are situations in shell code where the difference between a case-match or string-suffix-replace written in shell and a process spawn matters. Not only because forking a process for one simple string operation is wasteful (cost: about 1ms), but also because of the semantic problems that come with child processes (error handling).