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I'd like to write a script that reads a file and passes every line as options (or "option arguments") to a command, like this:

command -o "1st line" -o "2nd line" ... -o "last line" args

What's the simplest way of doing this?

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2 Answers 2

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# step 1, read the lines of the file into a shell array
mapfile -t lines < filename

# build up the command
cmd_ary=( command_name )
for elem in "${lines[@]}"; do
    cmd_ary+=( -o "$elem" )
done
cmd_ary+=( other args here )

# invoke the command
"${cmd_ary[@]}"
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  • This. Although you'll want to maybe check the file for total number of lines (or other delimiter) so that you don't call your command with more arguments than it can handle - might want to read up on this (old) article and then check for newer references - in-ulm.de/~mascheck/various/argmax
    – ivanivan
    Commented Nov 8, 2017 at 22:43
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Here is one possibility:

$ cat tmp
1st line
2nd line
3rd line
4th line
$ command $(sed 's|.*|-o "&"|' tmp | tr '\n' ' ')

As glennjackman points out in the comments, word splitting can be circumvented by wrapping in eval, though the security implications of doing so should be appreciated:

$ eval "command $(sed 's|.*|-o "&"|' tmp | tr '\n' ' ')"

Edit: Combining my suggestion of using sed to assemble arguments with glenn jackman's mapfile/readarray approach gives the following concise form:

$ mapfile -t args < <(sed 's|.*|-o\n&|' tmp) && command "${args[@]}"

As a trivial demonstration, consider the aforementioned tmp file, the command grep, and the file text:

$ cat text
some text 1st line and
a 2nd nonmatching line
some more text 3rd line end
$ mapfile -t args < <(sed 's|.*|-e\n&|' tmp) && grep "${args[@]}" text
some text 1st line and
some more text 3rd line end
$ printf "%s\n" "${args[@]}"
-e
1st line
-e
2nd line
-e
3rd line
-e
4th line
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  • Unfortunately, this will not maintain the lines as whole elements due to the shell's word splitting. Try where the command is printf "%s\n" -- instead of receiving 8 arguments (-o 1st line ...), this technique will give the command 12 arguments containing literal quote chars (-o "1st line" -o "2nd line" etc). You could do eval "command $(sed ...)" but that's nasty and fragile. Commented Nov 8, 2017 at 20:41
  • @glennjackman: Agreed, eval would be needed to avoid the word splitting problem; your command array-based approach is better for general use.
    – user001
    Commented Nov 8, 2017 at 21:05

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