I want to pass all the files as a single argument on Linux but I am not able to do that.
This is working
ls | sort -n | xargs -i pdftk {} cat output combinewd2.pdf
This passes a single argument per command, but I want all in one command.
Two Types of Commands Using Multiple Arguments Commands can have multiple arguments in two scenarios: All command arguments – COMMAND ARG1 ARG2 ARG3. Option arguments – for example, COMMAND -a ARG1 -b ARG2 -c ARG3.
The -c flag to sh only accepts one argument while xargs is splitting the arguments on whitespace - that's why the double quoting works (one level to make it a single word for the shell, one for xargs).
The xargs command builds and executes commands provided through the standard input. It takes the input and converts it into a command argument for another command. This feature is particularly useful in file management, where xargs is used in combination with rm , cp , mkdir , and other similar commands.
xargs will run the first two commands in parallel, and then whenever one of them terminates, it will start another one, until the entire job is done. The same idea can be generalized to as many processors as you have handy. It also generalizes to other resources besides processors.
Use -I
option:
echo prefix | xargs -I % echo % post
Output:
prefix post
This is one way to do it
pdftk $(ls | sort -n) cat output combinewd2.pdf
or using backtick
pdftk `ls | sort -n` cat output combinewd2.pdf
For example, if the filenames are 100, 2, 9, 3.14, 10, 1 the command will be
pdftk 1 2 3.14 9 10 100 cat output combinewd2.pdf
To handle filenames with spaces or other special characters consider this fixed version of @joeytwiddle's excellent answer (which does not sort numerically, see discussion below):
#-- The following will handle special characters, and # will sort filenames numerically # e.g. filenames 100, 2, 9, 3.14, 10, 1 results in # ./1 ./2 ./3.14 ./9 ./10 ./100 # find . -maxdepth 1 -type f -print0 | sort -k1.3n -z -t '\0' | xargs -0 sh -c 'pdftk "$@" cat output combinewd2.pdf' "$0"
xargs
is an external command, in the previous example it invokes sh
which in turn invokes pdftk
.
An alternative is to use the builtin mapfile
if available, or use the positional parameters. The following examples use two functions, print0_files generates the NUL terminated filenames and create_pdf invokes pdftk
:
print0_files | create_pdf combinewd2.pdf
The functions are defined as follows
#-- Generate the NUL terminated filenames, numerically sorted print0_files() { find . -maxdepth 1 -type f -print0 | sort -k1.3n -z -t '\0' }
#-- Read NUL terminated filenames using mapfile create_pdf() { mapfile -d '' pdftk "${MAPFILE[@]}" cat output "$1" }
#-- Alternative using positional parameters create_pdf() { local -r pdf=$1 set -- while IFS= read -r -d '' f; do set -- "$@" "$f"; done pdftk "$@" cat output "$pdf" }
As pointed out in the comments the simple initial answer does not work with filenames containing spaces or other special characters. The answer by @joeytwiddle does handle special characters, although it does not sort numerically
#-- The following will not sort numerically due to ./ prefix, # e.g. filenames 100, 2, 9, 3.14, 10, 1 results in # ./1 ./10 ./100 ./2 ./3.14 ./9 # find . -maxdepth 1 -type f -print0 | sort -zn | xargs -0 sh -c 'pdftk "$@" cat output combinewd2.pdf' "$0"
It does not sort numerically due to each filename being prefixed by ./
by the find
command. Some versions of the find
command support -printf '%P\0'
which would not include the ./
prefix. A simpler, portable fix is to add the -d, --dictionary-order
option to the sort
command so that it considers only blank spaces and alphanumeric characters in comparisons, but might still produce the wrong ordering
#-- The following will not sort numerically due to decimals # e.g. filenames 100, 2, 9, 3.14, 10, 1 results in # ./1 ./2 ./9 ./10 ./100 ./3.14 # find . -maxdepth 1 -type f -print0 | sort -dzn | xargs -0 sh -c 'pdftk "$@" cat output combinewd2.pdf' "$0"
If filenames contain decimals this could lead to incorrect numeric sorting. The sort
command does allow an offset into a field when sorting, sort -k1.3n
, one must be careful though in defining the field separator if filenames are to be as general as possible, fortunately sort -t '\0'
specifies NUL as the field separator, and the find -print0
option indicates NUL is to be used as the delimiter between filenames, so sort -z -t '\0'
specifies NUL as both the record delimiter and field separator-- each filename is then a single field record. Given that, we can then offset into the single field and skip the ./
prefix by specifying the 3rd character of the 1st field as the starting position for the numeric sort, sort -k1.3n -z -t '\0'
.
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