1

I'm trying to somehow use xargs so a program whose outputs are the lines

<ARG1>
<ARG2>
 ...
<ARGN>

will cause the execution of the following command:

command
    <GLOBAL_PREFIX_1> \
    <GLOBAL_PREFIX_2> \
    ...               \
    <PREFIX1> <PREFIX2> ... ARG1 <SUFFIX1> <SUFFIX2> ... \
    <PREFIX1> <PREFIX2> ... ARG2 <SUFFIX1> <SUFFIX2> ... \
                            ...                          \
    <PREFIX1> <PREFIX2> ... ARGN <SUFFIX1> <SUFFIX2> ... \
    <GLOBAL_SUFFIX_1> \
    <GLOBAL_SUFFIX_2> \
    ...

where the prefixes and suffixes are known beforehand, but arbitrary.

Some (probably) obvious notes that I feel like I have to explicitly state anyway:

  • The parameters are not "nice". They lack newlines but might contain spaces, $, (, ), ", etc.

  • I would like to avoid converting them to a single giant string and back if at all possible.

  • Yes, I meant what I wrote. I really just only want 1 command to run: not 0, not 2, not 3, not N...

  • More generally: I don't want to spawn a new process for each argument.

  • Simpler tools are preferred, assuming correctness is given... so xargs is preferred over sed, which is preferred over awk, etc.

  • I'm trying to use standard *nix shell tools here.
    Obviously I can write a Python script, but that's not the point...

1

Forget xargs, just use a while loop. This assumes that printf is builtin

#!/bin/sh
printf "%s\n" "command"
printf "    %s\\\n" "<GLOBAL_PREFIX_1>" "<GLOBAL_PREFIX_2>" "..."
while read -r ; do
    printf "    <PREFIX1> <PREFIX2> ... %s <SUFFIX1> <SUFFIX2> ... \\\n" "$REPLY"
done
printf "    %s\\\n" "<GLOBAL_SUFFIX_1>" "<GLOBAL_SUFFIX_2>"
printf "    %s\n" "..."

If the PREFIXn or SUFFIXn have interesting characters in them like % or \ then these will need to be escaped.

Of course sed would work

sed '1i\
GP1\\\
GP2\\\
...\\
s/.*/P1 P2 & S1 S2\\/
$s/.*/&\
GS1\\\
GS2\\\
... '

For awk you have BEGIN and END clauses....

  • The first one spawns a new process per argument I believe, right? (Or at least it does on my system.) The sed one seems like it doesn't though? – user541686 Nov 28 '16 at 7:18
  • Use a shell which has printf as a builtin, like bash, ksh, zsh. – icarus Nov 28 '16 at 7:31
  • Oh, actually, I assumed it wasn't a builtin because I saw /usr/bin/printf... but it seems it's listed under help (for BASH) too, never mind. Thanks! +1 – user541686 Nov 28 '16 at 7:39
0

If the arg prefix and arg postfix does not contain space, then GNU Parallel's -X is made for you:

seq 1000 | parallel -X echo global prefix argpre{}argpost global postfix

It will distribute evenly to the number of core. If you do not like that:

seq 1000 | parallel -j1 -n10 -X echo global prefix argpre{}argpost global postfix

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