If you want to print most of the files in a large directory,
put the output of ls
into a file.
Edit the file to leave just the filenames you want printed.
Give the file to xargs
' standard input:
ls > allfiles.tmp
xargs lpr < allfiles.tmp
What did that do?
With lines like these in allfiles.tmp
ran one or more lpr
commands, each with a group of
arguments, until it had read every word in the file:
lpr afile application ...
lpr ... yoyotest zapme
The standard output of xargs
is the standard output of the
commands it runs.
So, if you'd created allfiles.tmp
above but you wanted to format
the files with
first, you could type:
xargs pr < allfiles.tmp | lpr
would run all of these pr
The shell would pipe their standard outputs
to a single lpr
pr afile application ...
pr ... yoyotest zapme
In this next example,
gets a list of all files in the directory tree.
Next, we use xargs
to read those filenames and run
to find which files contain the word "WARNING."
Next, we pipe that to a setup with pr
, like the one
in the previous example:
find . -type f -print | xargs grep -l WARNING | xargs pr | lpr
"Huh?" you might say.
Just take that step by step.
The output of find
is a list of filenames, like
./afile ./bfile ... ./adir/zfile
and so on.
The first xargs
gives those filenames to one or more grep -l
grep -l WARNING ./afile ./bfile ...
grep -l WARNING ./adir/zfile ...
The standard output of all those grep
s is a (shortened) list of
filenames that match.
That's piped to another xargs
-it runs pr
commands with the
filenames that grep
UNIX is weird and wonderful!
Sometimes you don't want xargs
to run its command with as many
arguments as it can fit on the command line.
option sets the maximum number of arguments xargs
will give to each command.
Another handy option, -p
, prompts you before running each command.
Here's a directory full of files with errors (whose names end with
) and corrected versions (named .fixed
I use ls
to give the list of files to xargs
; it reads two
filenames at once, then asks whether I want to run diff -c
those two files.
It keeps prompting me and running diff -c
until it runs out of file pairs:
ls | xargs -p -n2 diff -c
diff -c chap1.bad chap1.fixed ?...
...Output of diff command for chap1
diff -c chap2.bad chap2.fixed ?...
diff -c chap3.bad chap3.fixed ?...
...Output of diff command for chap3