If I have a list of files say file1 ... file20, how to I run a command that has the list of files as the arguments, e.g. myccommand file1 file2 ... file20?
3 Answers
If your list is in your argument vector -- that is to say, if you were started with:
./yourscript file1 file2 ...
then you'd run
mycommand "$@"
If your list is in an array:
mycommand "${my_list_of_files[@]}"
If your list is in a NUL-delimited file:
xargs -0 -- mycommand <file_with_argument_list
If your list is in a newline-delimited file (which you should never do for filenames, since filenames can legitimately contain newlines):
readarray -t filenames <file_with_argument_list
mycommand "${filenames[@]}"
If by "list", you just mean that you have a sequence of files:
mycommand file{1..20}
...or, to build an array of filenames with numeric components from a range more explicitly in cases where {1..20} doesn't work (such as when 20 is a variable):
max=20 # to demonstrate something you can't do with brace expansion
list=( )
for ((i=0; i<max; i++)); do
list+=( file"$i" )
done
mycommand "${list[@]}"
10 Comments
rhlee
Yes, sorry about the confusion, by "list" I meant sequence of files.
mycommand file{1..20} worked perfectly, thanks.
Akaisteph7
But then how does
mycommand accept this list with other arguments?
Charles Duffy
@Akaisteph7, the argument vector is a flat list -- there's no support for nested structures at the underlying OS level, so everything is necessarily turned into just one list of strings.
Akaisteph7
I see. So essentially, a regular list in your examples would just be passed as a single, space-delimted string that can then be split up again from
mycommand.Charles Duffy
@Akaisteph7, ...as for this answer, to be 100% unambiguous: Absolutely none of the practices I showed generates a string with contents concatenated into a single space-separated argument; in every case, without exceptions, each array entry becomes a separate argument-list entry. (If by contrast someone used
"${array[*]}" instead of "${array[@]}", then you'd get the first character of IFS -- by default a space -- separating the elements) |
Look into the shift bash command (man bash). You can iterate, taking $1 each time.
for n in $(seq 1 $#); do
echo $1
shift
done
Call this file myshift.sh. Then
$ ./myshift.sh a b c
a
b
c
4 Comments
chepner
for loops already have a standard way of iterating over command-line arguments. This is just a non-standard way of writing for n; do echo "$n"; done.Charles Duffy
Also,
seq is nonstandard -- it's an external binary, not built into the shell, and not mandated by POSIX for operating systems to provide -- and you're paying extra time to start it up.
NYRecursion
@CharlesDuffy Thanks for the downvote. I observe that Mark Reed (below), with 98.8k, suggests
seq. Where's his downvote?Charles Duffy
I hadn't noticed, but you're right; added one there too.
If you're generating a list of files with seq, you can just use command substitution to drop them into the command line:
mycommand $(seq ...)
although that will fail if the filenames so generated have any spaces (or tabs or newlines...) in them.
You can also use bash's curly-brace expansion to generate them instead of seq, for instance file{1..10} to generate file1 file2 file3 file4 file5 file6 file7 file8 file9 file10. This has the advantage of working even if the filename contains spaces in the common part, as long as you quote it properly (e.g. "file name"{1..10}).
2 Comments
rhlee
Yep, the curly bracket expansion works. It's a shame I can't mark multiple answers as the "correct one".
Mark Reed
Well, that part of my answer was redundant with the one you accepted anyway. The only reason I answered at all was because you had added a comment about
seq that hadn't been addressed yet. Not sure that's enough to leave this answer here..
seqcommand.