HPR2793: bash coproc: the future (2009) is here

Hacker Public Radio

If you want the full manuscript, that’s at gitlab: hpr2793_bash_coproc_manuscript.adoc. It’s almost a transcript, but I added spontaneous commentary while reading the examples, so that’s not in the manuscript. Episode errata: Command substitution with $() is perfectly valid according to POSIX, and is accepted both by dash and by bash --posix. It’s not to be considered a bashism. I fumbled the pronunciation of the printf format string in one place and said "parenthesis" instead of "percentage sign". I tried to say "space" every time there’s a space, but I know I forgot it in a few places. But you probably need to look at the show notes to really make sense of the commands anyway. Example #1: $ echo $(echo hacker public radio) hacker public radio $ $(echo echo hacker public radio) # It can even supply the command itself, not just parameters. Note the word splitting. hacker public radio $ "$(echo echo hacker public radio)" # Counteract word splitting by putting the command substitution in quotes. bash: echo hacker public radio: command not found $ `echo echo hacker public radio` # Old-style command substitution hacker public radio More on command substitution in Dave’s hpr1903: Some further Bash tips. Example #2: $ echo <(echo hacker public radio) /dev/fd/63 $ cat <(echo hacker public radio) hacker public radio You can also combine process substitution with redirection. Example #3: $ echo hacker public radio > >(sed -e 's/$/!/') # You need the space between the greater-thans here! hacker public radio!