Bash – Pass a pipe to a command that expects a filename

bashcommandpipe

Say I have a command foo which takes a filename argument: foo myfile.txt. Annoyingly, foo doesn't read from standard input. Instead of an actual file, I'd like to pass it the result of another command (in reality, pv, which will cat the file and output a progress meter as a side effect).

Is there a way to make this happen? Nothing in my bag of tricks seems to do it.

(foo in this case is a PHP script which I believe processes the file sequentially).

I'm using Ubuntu and Bash

EDIT
Sorry for the slightly unclear problem description, but here's the answer that does what I want:

pv longfile.txt | foo /dev/stdin

Very obvious now that I see it.

Best Answer

If I understand what you want to do properly, you can do it with bash's command substitution feature:

foo <(somecommand | pv)

This does something similar to what the mkfifo-based answers suggest, except that bash handles the details for you (and it winds up passing something like /dev/fd/63 to the command, rather than a regular named pipe). You might also be able to do it even more directly like this:

somecommand | pv | foo /dev/stdin

Related Solutions

Linux – Unzipping files that are flying in through a pipe

While a zip file is in fact a container format, there's no reason why it can't be read from a pipe (stdin) if the file can fit into memory easily enough. Here's a Python script that takes a zip file as standard input and extracts the contents to the current directory or to a specified directory if specified.

import zipfile
import sys
import StringIO
data = StringIO.StringIO(sys.stdin.read())
z = zipfile.ZipFile(data)
dest = sys.argv[1] if len(sys.argv) == 2 else '.'
z.extractall(dest)

This script can be minified to one line and created as an alias.

alias unzip-stdin="python -c \"import zipfile,sys,StringIO;zipfile.ZipFile(StringIO.StringIO(sys.stdin.read())).extractall(sys.argv[1] if len(sys.argv) == 2 else '.')\""

Now unzip the output of wget easily.

wget http://your.domain.com/your/file.zip -O - | unzip-stdin target_dir

Linux – How to run a command multiple times, using bash shell

I don't think a command or shell builtin for this exists, as it's a trivial subset of what the Bourne shell for loop is designed for and implementing a command like this yourself is therefore quite simple.

Per JimB's suggestion, use the Bash builtin for generating sequences:

for i in {1..10}; do command; done

For very old versions of bash, you can use the seq command:

for i in `seq 10`; do command; done

This iterates ten times executing command each time - it can be a pipe or a series of commands separated by ; or &&. You can use the $i variable to know which iteration you're in.

If you consider this one-liner a script and so for some unspecified (but perhaps valid) reason undesireable you can implement it as a command, perhaps something like this on your .bashrc (untested):

#function run
run() {
    number=$1
    shift
    for i in `seq $number`; do
      $@
    done
}

Usage:

run 10 command

Example:

run 5 echo 'Hello World!'

Best Answer

Related Solutions

Linux – Unzipping files that are flying in through a pipe

Linux – How to run a command multiple times, using bash shell

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